9th. World Congress on Parasitic Plants
Charlottesville, VA 3-7 June 2007
Ahom, RI, and Okereke, OU. Varietal Differences in Ability of Sesame and Pigeon pea as Trap Crops to Induce Suicidal Seed Germination in Striga hermonthica (Scrophulariaceae)
Alejandro Pérez-de-Luque. Mechanisms of Resistance to Parasitic Plants: from Field Screenings to Laboratory Microscopic Studies
Alers-Garcia, J, and Bever, JD. Size Dependent Parasitism of Cuscuta gronovii: Its Implications on Host Population Size Structure and Dynamics
Alers-Garcia, J, Lewis, KC, and Wright, LJ. Parasite Mediated Maternal Effects in Bitter and Sweet Lupins
Aly, R, Shomin, H, Joel, DM, Steinitz, B, Zelcer, A, and Gal-On, A. A New Approach to Parasitic Weed Control Based on Silencing of a Key Metabolic Gene in the Parasite
Aouali, S, Bouznad, Z, Zermane, N, El Khishine, D, Madkour, M, Faied, M, Chaabane, M. Genetic Diversity Among Orobanche crenata Ecotypes Revealed by RAPD and AFLPs Markers, in Algeria
Bewick, TA., and Cascino, J. Development of a Biological Herbicide for Control of Cuscuta spp.
Bolin, JF, Tennakoon, KU, and Musselman, LJ. Stable Isotope and Nutrient Relationships of the Root Holoparasite Hydnora (Hydnoraceae) in Southern Africa
Bouwmeester, HJ , Cardoso, C, Zhongkui, S, Matusova, R , Lopez-Raez, JA, Charnikhova, T, Verstappen, FWA , Rochange, S, Bécard, G, and Ruyter-Spira, C. Strigolactones, Signals for Friends and Enemies
Cameron, DD, Keith, AM, and Seel, WE .Rhinanthus minor as an Ecosystem Engineer: Understanding the Mechanistic Basis of Parasitic Plant-Induced Changes in Community Structure.
Castillejo, MA, Maldonado, AM, Dumas-Gaudot, E, Pérez de Luque, A, Rubiales, D, and Jorr’n, J. Differential expression proteomics to investigate responses and resistance to Orobanche crenata in legumes
Chachalis, D, and Murdoch, AJ. Potential Use of Nijmegen-1 and Smoke Water Solutions to Deplete Orobanche ramosa Seed Banks in Greece
Chiang, MY, Hsieh, YC, Yuan, CI, and Lin, FY. Cuscuta Species in Taiwan: Molecular Differentiation and Related Findings
De Mol, M, and Heller, A Sap Flow from Host to Mistletoe: an Anatomical Approach
de Zélicourt, A, Letousey, P, Thoiron, S, Montiel, G, Simier, P, and Delavault, P. Molecular analysis of resistance mechanisms to Orobanche cumana in sunflower
dePamphilis, C, McNeal, J, and Zhang, Y. Genome Evolution in Parasitic Plants: New Genomes, Surprising Findings
Dewaele, D, Elsen, A, and Obiudoh, CA. A Study of Biodiversity of African Radopholus Similis In Uganda.
Dhanapal, GN, Borg, SJ ter, and Struik, PC(3)Integrated Management of Broomrape in India
Draie, R, Pouvreau, JB, Véronési, C, Théodet, C, Thoiron, S, Delavault, P and Simier, P. The Sucrose-Degrading Enzymes in Orobanche ramosa. Characterization and Involvement in Growth, Cell Wall Synthesis and Starch Accumulation.
Dubé, M-P, and Belzile, FJ. Genetic variability among five races of Striga gesnerioides (Willd.) Vatke detected by ISSR, AFLP and cpSSR analysis.
Dunlavey, R, Logan, BA and Reblin, JS. The Influence of Arceuthobium pusillum Infection on the Hydraulic Architecture of White Spruce Stems
Dzomeku, IK, and Murdoch, AJ. Studies on Seed Dormancy, Germination and Seedling Emergence of Striga Hermonthica
Echevarr’a-Zome–o, S, Pérez-de-Luque, A, Jorr’n, J, and Maldonado, AMHistochemical analysis of defense responses involved in resistance of sunflower ( Helianthus annuus ) to Orobanche cumana
Eizenberg, H, Ephrath, J, Lande, T, Achdari, G, and Hershenhorn, J. Temporal Thermal and Special Model for Orobanche Management.
Elzein, A, Fen, B, Kroschel, J, Marley, P, and Cadisch, G. Synergy Between Striga- Mycoherbicides "Fusarium oxysporum f.sp. strigae" and Resistant Cultivars Under Field Conditions: Step Towards Integrated Striga Control in Africa.
Elzein, A, Kroschel, J, Fen, B, Marley, P, and Cadisch, G. Compatibility of Striga-Mycoherbicides with Fungicides Delivered Using Seed Treatment Technology and its Implication For Striga and Cereal Fungal Diseases Control.
Fan, ZW, Buschmann, H, Shen, YD, Lu, Y, and Sauerborn, J. Induced Host Resistance as a Control Method for Parasitic Weeds
Fernández-Aparicio, M, Flores, F, Pérez-de-Luque, A and Rubiales, D. Yield losses in pea as a function of Orobanche crenata levels of infection.
Fernández-Aparicio, M, Pérez-de-Luque, A, and Rubiales, D. Response of Medicago truncatula Accessions to Various Species of Orobanche.
Fernández-Aparicio, M, Pérez-de-Luque, A, Sillero, JC and Rubiales, D. Yield increase in oat-faba bean intercrops under heavy Orobanche crenata infections.
Funk, H, Berg, S, Krupinska, K, Maier, U and Krause, K. Complete DNA Sequences of the Plastid Genomes of Two Parasitic Flowering Plant Species, Cuscuta reflexa and Cuscuta gronovii.
Gebeyehu, S, Belayneh, A and Tesfamariam, M. Parasitic Weeds in Ethiopia: Challenges to Resource Poor and Small Scale Farmers.
Gharib, C, Haidar ,MA, Sleiman, FT. and Sidahmed, MM. Germination and Viability of Cuscuta spp. (Dodder) Seeds after Digestion in Sheep Rumen.
Goldwasser, Y, Yoneyama, K, Xie, X, and Yoneyama, K. Identification of the Stimulants Produced by Arabidopsis thaliana Responsible for the Induction of Orobanche Seed Germination.
Gunathilake, P, Tomilov, A, Tomilova, N, Fillapova, T and Yoder, JI. Macromolecular Trafficking from Host Plants into the Hemiparasitic Plant Triphysaria versicolor.
Haddad, A and Pala, M. Significance of Parasitic Weeds for Food Legumes in Syria.
Harrison, MJ. The Arbuscular Mycorrhizal Symbiosis; Genomics Approaches to Dissect Development and Function.
Heller, A, Elzein, A, De Mol, M, Kroschel, J and Cadisch, G. Colonization of F. oxysporum f.sp. strigae (Foxy 2) on roots of sorghum plants and its implication for Striga control using a seed treatment delivery system: an anatomical study.
Hšniges, A, Ardelean, A, and Wegmann, K. Ecological and Physiological Investigations on Orobanche Species in the Spontaneous Flora of Romania
Kaldenhoff, RWE. Molecular Events During Cuscuta Infection.
Kanampiu, F. Striga Weed Management Options under Smallholder Agriculture in Africa.
Kusumoto, D, Yoneyama, K, Yoneyama, K, Takeuchi, Y. Induction of Systemic Acquired Resistance in Root Parasitic Weeds.
Lanini, WT, Miranda, M, and Aouali, S. Dodder (Cuscuta pentagona) Control in Roundup Ready Alfalfa.
Liu, Y, Liang, L and Lynn DG. Gene Regulation during Haustorial Development and Shoot Initiation in Striga asiatica.
Lopez-Raez, JA, Charnikhova, T , Gomez-Roldan, V, Matusova, R , de Vos, R, Schipper, B, Verstappen, F , Bino, R , Becard, G, and Bouwmeester, HJ. The Biosynthesis of the Tomato Germination Stimulants is Promoted by Phosphate Starvation.
Lozano-Baena, MD, Lindsey, K, Moreno MT, Rubiales, D, and Pérez-de-Luque, A. Laser Capture Microdissection (LCM): New Technologies Apply to Study of the Parasitic Plant Interactions.
Lozano-Baena, MD, Moreno, MT, Rubiales, D, and Pérez-de-Luque A. Analyses of Medicago truncatula Resistance Against Orobanche crenata Using Citochemical Techniques.
Matusova, R , and Bouwmeester, HJ. The Strigolactone Germination Stimulants of the Plant-Parasitic Striga and Orobanche spp are Derived from the Carotenoid Pathway.
Miegel, D, Hayton, D, and Matthews, JM. Seedbank and Seedbank Management of Orobanche ramosa in South Australia.
Murdoch, AJ, and Kebreab. Predictive Empirical Modeling of Parasitic Weed Life Cycle.
Nickrent, DL, and Vidal-Russell, R.The Evolutionary Origins of Aerial Parasitism in Santalales.
Ogbebor, NO, Omorusi, VI and Evueh, GA. Evaluation of Mistletoe Incidence on Nine Rubber Clones and its Effects on Latex Yield in Nigeria.
Okazawa, A, Wada, Y, Fukusaki, E, Yoneyama, K, Takeuchi, Y, and Kobayashi, A. Trehalose Promotes Seed Germination of a Holoparasitic Plant, Orobanche minor Sm.
Pacureanu-Joita, M, Raranciuc, S, Procopovic, E, and Sava, EAO - 548, a Sunflower Inbred Line, Carrying Two Genes for Resistance Against a New Highly Virulent Romanian Population of Orobanche cumana.
Palmer, AG, Liang, L, OÕMalley, R, and Lynn, DG. Calcium Mediated Transduction of Haustorial Inducing signals in Striga asiatica.
Palmer, AG, Liang, L, Keyes, J, and Lynn, DG. ROS production and Semagenesis in Pathogenesis.
Palmer, J. Horizontal Gene Transfer Gone Wild in Parasitic and Other Flowering Plants.
Plakhine, D, Tadmor, Y, Levin, I and Joel, DM. Non-Stimulated Spontaneous Germination of Orobanche is Genetically Controlled.
Riches, CR, and Mbwaga, AM. Green manure: A Striga Management Technology Whose Time Has Come?
Roney, JK, Khatibi, PA, Stromberg, VK, and Westwood, JH. Trafficking of Host mRNAs into Dodder: A New Frontier in Host-Parasite Communication.
Saadoun, I, Hameed, KM, Ababneh, Q, Bataineh, S and Foy, CL. Biological Control of Orobanche cernua Seed Germination Utilizing an Indigenous Actinomycete Isolate in Jordan.
Sandler, HA. Integrating Germination Patterns, Chemical, and Nonchemical Options to Manage Swamp Dodder in Massachusetts Cranberry Production.
Schneeweiss, GM, Park, JM, Manen, JF, and Colwell, AE. Phylogeny and Evolution of Orobanche and Related Genera (Orobanchaceae).
Scholes J., and Press, M. The Molecular Basis of Susceptibility and Resistance to Striga: insights from Transcript Profiling.
Shamoun, SF, Rietman, LM, Askew, SE, and van der Kamp, BJ. Development of a Biological Control Strategy for Management of Hemlock Dwarf Mistletoe in Coastal British Columbia, Canada.
Sugimoto, Y, Ueyama, T, and Yasuda, N. In vitro Production of Strigolactones by Plant Root Cultures.
Takagi, K, Okazawa, A, Wada, Y, Trakulnaleamsai, C, Fukusaki, E, Yoneyama, K, Takeuchi, Y, and Kobayashi, APhotoresponse Analysis of Phytochrome A in the Non-photosynthetic Parasitic Plant; Orobanche minor Sm.
Tennakoon, KU, Bolin, JF, and Musselman, LJ. Structural and Functional Attributes of the Hypogeous Root Holoparasite Hydnora triceps Drege & Meyer (Hydnoraceae).
Stefanovic, S, and Costea, M. Reticulate Evolution in the Parasitic Genus Cuscuta (Dodders; Convolvulaceae).
Tennakoon, KU. Potential of Establishing Root Hemiparasitic Sandalwood (Santalum album L.) as a NTF Species in the Buffer Zones of Forests and Degraded Lands in Australasia: a Sri Lankan Experience.
Thorogood, CJ, Rumsey, FJ, and Hiscock, SJ. Speciation and Host Specificity in Orobanche.
Timko, MP,Gowda, BS, Li, J, and Lis, K, Deciphering the Interaction of Striga with Hosts and Non-hosts.
Tomilov, A, Tomilova, N, Filappova, T, Gunathilake, P, Wu, D-Y, Hoang, N, and Yoder, JI. Early Haustorium Development in Triphysaria: A View from Inside the Nucleus.
van der Kooij,TAW, Krupinska K, and Krause, K. Characterization of the Tocochromanol Content and Composition of Different Species of the Parasitic Flowering Plant Genus Cuscuta.
Virupakshaiah, DBM, Ameresh, SH, and Mirji, SB. Structure Analysis of Computer Generated Homologous Models of pm3 Protein in Triticum aestivum (Wheat).
Wegmann K. 2000 Years of Observation, Knowledge and Research on Orobanche.
Williams, AM, and Virtue, JG. Calculation of Growing Degree Days to Determine Optimum Timing of Herbicide Application for Control of Branched Broomrape Orobanche ramosa in Pastures.
Xie, X, Awad, AA, Yoneyama, K, Sekimoto, H, Kusumoto, D, Takeuchi, Y, Yoneyama, K. Qualitative and Quantitative Differences of Strigolactone Exudation Determine Host Specificity of Root Parasites Orobanche and Striga.
Yoneyama, K, Sekimoto, H, Takeuchi, Y, and Yoneyama, K. Nitrogen and Phosphorus Deficiencies Promote the Production and Exudation of 5-Deoxystrigol in Sorghum.
Yonli, D, Traoré, H, Sérémé, P, Hess, DE, and Sankara, P. Integrated Striga hermonthica Management Based Fusarium.
Yoshida, S, and Shirasu, K. Agrobacterium-Mediated Transformation of Striga hermonthica.
Ahom, RI (1), and Okereke, OU (2)
Varietal Differences in Ability of Sesame and Pigeon pea as Trap Crops to Induce Suicidal Seed Germination in Striga hermonthica (Scrophulariaceae)
1. Department of Crop and Environmental Protection, University of Agriculture, Makurdi, Benue State, Nigeria. Email: ie
2. Department of Crop Science, University of Nigeria, Nsukka
Striga hermonthica is the most serious constraint to maize production in West Africa Savannah. Seventeen (17) varieties of sesame and 13 accessions of pigeon pea were evaluated for their ability to stimulate Striga seed germination in vitro using cut-root technique. The test crop varieties evaluated showed significant differences in their ability to stimulate seed germination in S. hermonthica. On the basis of the results, the trap crops varieties were grouped into five with respect to stimulant production, viz., very high, high, moderate, low and very low. For Sesame: Very high (none), high (69B and Yandev _ 55) moderate (Ex-Pankshin-98, 73A-79B, Cross-95, E-8, Ncriben-01M, 73A-H2B, 60-2-3-1-8B and Ciano-16), Low (Yandev-75, Type-4, Ciano _ 27, Eva and 69-1-1) and very low (Pachequeno and Ncriben-03L). For Pigeon pea: very high (TCC1035, Cita 4, TCC6, TCC8126, Cita 3, TCC 87 and Cita 2), high (TCC2, TCC 8127, TCC 151, and Cita 1), and moderate (TCC8 and TCC 8129). The use of trap crops, which stimulate suicidal seed germination in Striga fits into the cultural practices of the small - scale farmer in Nigeria. The traps crops used in this study are cash crops and commonly grown in Benue State - Nigeria. However, varietal differences exist between and within trap crops. The varieties of sesame and pigeon pea belonging to the very high and high stimulants production groups are therefore recommended for use by farmers in Nigeria to clean up or reduce the reserve of Striga seeds in the soil.
Alers-Garcia, J (1), Lewis, KC (1), and Wright, LJ (1)
Parasite Mediated Maternal Effects in Bitter and Sweet Lupins
1. Rowland Institute at Harvard, 100 Edwin H. Land Blvd., Cambridge, Massachusetts, 02142, USA. E-mails: alers-garcia[at]rowland.harvard.edu, lewis[at]rowland.harvard.edu, wright[at]rowland.harvard.edu.
A strong emphasis has been placed in the study of parasitic plants in forestry and agricultural settings given the potential for economic losses these "pests" have in their hosts via marked changes in growth, allometry and in many cases total crop failure. Most studies have overlooked the fact that parasitic plants can directly affect the growth environment of the maternal parent and thereby the development, size, viability and chemical composition of its progeny. Our research focuses on environmentally-mediated maternal effects of Castilleja indivisa, a hemiparasite, on high and low alkaloid content isogenic lines of Lupinus albus. We are particularly interested in examining the role and mechanisms by which the parasite affects host nutritional content and its implications in plant defense and reproduction. Castilleja indivisa is known to alter nutrient availability and allocation patterns of its hosts. Castilleja preferential uptake of N from its hosts is expected to result in a reduction in growth rate of host sinks (flowers and fruits) and seed provisioning (i.e. quality). Parasitized hosts are predicted to have lower seed size and greater seed C: N ratios than unparasitized hosts. However, since the intensity of parasitism is usually correlated with host N content, we predict a greater magnitude of maternal effects on high alkaloid hosts compare to low alkaloid hosts.
Alers-Garcia, J (1), and Bever, JD (2)
Size Dependent Parasitism of Cuscuta gronovii: Its Implications on Host Population Size Structure and Dynamics
1. Rowland Institute at Harvard, 100 Edwin H. Land Blvd., Cambridge, Massachusetts, 02142, USA. E-mail: alers-garcia[at]rowland.harvard.edu.
2. Department of Biology, Indiana University, 1001 East Third St., Bloomington, Indiana 47405-3700, USA. E-mail: jbever[at]indiana.edu.
Parasitic plants can have negative effects on the fitness of their hosts. However less is known of how parasitic plants affect the population properties of their host plants. Our research focuses on the genus Cuscuta (dodder), a holoparasitic plant that exhibits active host choice. We particularly examined: 1) the effects of parasitism by Cuscuta gronovii on mean population performance and size structure of its host Pilea pumila, 2) the mechanisms underlying active host choice in dodder, and 3) the relationship between size dependent selection and length of the parasitic association on the interactions of individuals within a population. The results of our experiments show that size dependent parasitism and compensation at the population level are the mechanisms underlying the increase of size inequality on parasitized plant populations. Dodder selectively establishes on the tallest individuals, suppresses their growth and continues to spread onto unparasitized plants that have become taller. Dodder is able to discriminate among potential hosts and choose the tallest ones within the population at least fifteen days prior to parasitism. The effects of dodder on host individuals are dependent on the length of parasitism; dodder causes a drastic reduction on vegetative and reproductive parameters on early attacked hosts compared to those attacked later. Under the studied scenario as well as in situations on which host plant size exhibits a positive correlation with competitive dominance, parasite foraging behavior as well as the responses of unparasitized individuals are crucial in understanding and predicting the outcome of parasitism in population plant properties.
Aly, R (1), Shomin, H (1), Joel, DM (1), Steinitz, B (2), Zelcer, A (2), and Gal-On, A (1)
A New Approach to Parasitic Weed Control Based on Silencing of a Key Metabolic Gene in the Parasite
1. Department of Plant Pathology, Virology and Weed Research, ARO, Newe-Yaar Research Center, P.O.Box 1021, Ramat Yeshai 30095, Israel. E-mail: radi[at]volcani.agri.gov.il, shominh[at]gmail.com, dmjoel[at]volcani.agri.gov.il, amit[at]volcani.agri.gov.il
2. Department of Plant Genetics, ARO, The Volcani Center, Israel. E-mail: steintz[at]volcani.agri.gov.il, zelcer[at]volcani.agri.gov.il
The silencing approach has already been demonstrated as an effective control method against various pathogens. Gene silencing provides plants with defense against various pathogens, and is a tool of immense importance for research on plant development. The introduction of double-stranded RNA (dsRNA) proved to be a powerful tool for suppressing gene expression through a process known as post-transcriptional gene silencing in plants. In our study we used the inverted repeat technique for gene silencing of Mannose 6-phosphate reductase (M6PR), a key-gene in Orobanche spp. in order to provide the host plant with resistance against the parasite. A gene construct fusing the key gene for silencing to the binary vector (pBin-19) was already transformed to tobacco and tomato host plants. By PCR and RT-PCR analysis, transgenic plants were proved to have a specific PCR fragment (286 bp) which was designated on the mRNA of the O. aegyptiaca M6PR for silencing. Our results indicated that in-vitro production of small interfering RNAs (siRNAs) by introducing short double-stranded RNA molecules of the M6PR gene into O. aegyptiaca tubercles grown on tomato plants, facilitate suppression and degradation of the native M6PR mRNA, thereby reduction of total soluble solids (sugars) in the treated tubercles. Real-Time RT-PCR analysis showed that the endogenous M6PR mRNA of O. aegyptiaca tubercles or shoots grown on transgenic tomato plants harboring the M6PR silencing construct were reduced by 60-80% compared with the control (O. aegyptiaca grown on non-transgenic plants).
Aouali, S (1), Bouznad, Z (2), Zermane, N (2), El Khishine, D (3), Madkour, M (3), Faied, M (3), Chaabane, M (3)
Genetic Diversity Among Orobanche crenata Ecotypes Revealed by RAPD and AFLPs Markers, in Algeria
1. Institut Technique des Grandes Cultures, 1, rue Pasteur, Hassan-Badi BP16-El-Harrach- Alger-Algérie. E-mail: saouali[at]yahoo.fr
2. Institut National Agronomique, El-Harrach-Alger-Algérie. E-mail: bouznad[at]wissal.dz; nzermane[at]hotmail.com
3. Agricultural Engineering Research Institute (AGERI)-Cairo-Egypt. E-mail: el_khishin_dina[at]hotmail.com; m.madkour[at]cgiar.org; solygene[at]yahoo.com
The objectives of this study were to investigate the efficiency of RAPD and AFLP marker systems in detecting intraspecific genetic polymorphism, and to determine the level of diversity among six O. crenata ecotypes, from different geographical localities of El Mitidja. Ten decamer RAPD primers and, three AFLP primer combinations (EcRI/MseI), generated a total of 144 and 429 markers respectively. Dice's similarity matrices were prepared and used for analysis. The diversity index, effective multiplex ratio, and marker index values were higher for the AFLP. This technique appears to be more useful than RAPD in the analysis of limited genetic diversity among the 6 ecotypes of O. crenata tested. Both marker systems were able to discriminate among materials analyzed, but clear distinction between all ecotypes was obtained with AFLP markers. AFLP is therefore another tool for assessing genetic relationships among O. crenata ecotypes along with RAPD. The study, showed a proportional increase in genetic distance with geographical distance, when going from the center of El Mitidja to the eastern-center and the western-center respectively. It is probable that the dissemination center of this parasitic plant is the center of El Mitidja.
Bewick, TA. (1), and Cascino, J (2)
Development of a Biological Herbicide for Control of Cuscuta spp.
1. U.S. Department of Agriculture, Mailstop 2220, Washington, D.C. 20250
2. Sylvan Bioproducts, Inc, 198 Nolte Drive, Kittanning, Pennsylvania 16201
On May 18, 2005 the U.S. Environmental Protection Agency published a regulation that established an exemption from the requirement of a tolerance for residues of the microbial pesticide Alternaria destruens Strain 059, marketed commercially as Smolder_, on all agricultural commodities when applied and used in accordance with label directions for the control of dodder. This represented the culmination of 20 years of research but the beginning of efforts at commercial development. Large scale demonstrations were conducted in 2006 in several states in the U.S. with both a granular and a wetable powder formulation. Success was mixed. In Wisconsin cranberry fields, dodder control ranged from 52 to 100 per cent. In Massachusetts cranberry fields, dodder control ranged from 20 to 60 per cent. In Iowa carrot fields, dodder control ranged from 0 to 100 per cent. Differences in climatic conditions and, possibly, the genetic makeup of the dodder populations tested could account for this variability.
Bolin, JF (1), Tennakoon, KU (2), and Musselman, LJ (1)
Stable Isotope and Nutrient Relationships of the Root Holoparasite Hydnora (Hydnoraceae) in Southern Africa
1. Department of Biology, Old Dominion University, Norfolk, VA 23529, USA. E-mail: jbolin[at]odu.edu, lmusselm[at]odu.edu
2. Department of Botany, University of Peradeniya, Peradeniya 20400, Sri Lanka. E-mail: kushant[at]pdn.ac.lk
Hydnora is a genus of unusual plant parasites with a mainly African distribution. Most species of Hydnora reside underground and all lack stomata and leaves. Estimated transdermal water loss in Hydnora africana and Hydnora triceps rhizomes was 0.14_.02 and 0.19_.02 mg cm-1 hr-1, respectively. Due to its extremely water conservative nature Hydnora may be a useful model for parasite-host uptake. We measured carbon and nitrogen natural abundance stable isotope ratios for 11 Hydnora-host associations in southern Africa, including host plants with dominantly CAM or C3 metabolism. Hydnora-host isotope ratios were compared to 12 mistletoe-host associations, emphasizing relationships between host plants shared by Hydnora and mistletoes including Tapinanthus and Viscum species. Carbon and nitrogen isotope values for Hydnora are negatively correlated and carbon isotope ratios mirrored the host photosynthetic metabolism. For the first time we report mineral nutrition relationships for three holoparasite-CAM host associations. Total P and K levels were significantly elevated in the holoparasite relative to the host in most associations. Total Ca, Cl, Mg, N, Na, and S levels were significantly lower in the host.
Bouwmeester, HJ (1,2), Cardoso, C (1), Zhongkui, S (2), Matusova, R (1,2), Lopez-Raez, JA (2), Charnikhova, T (1), Verstappen, FWA (1,2), Rochange, S (3), Bécard, G (3) and Ruyter-Spira, C (1)
Strigolactones, Signals for Friends and Enemies
1. Laboratory for Plant Physiology, Wageningen University, Arboretumlaan 4, 6703 BD Wageningen, The Netherlands. E-mail: harro.bouwmeester[at]wur.nl; catarina.cardoso[at]wur.nl; radoslava.matusova[at]wur.nl; tatsiana.charnikhova[at]wur.nl; francel.verstappen[at]wur.nl; carolien.ruyter-spira[at]wur.nl
2. Plant Research International, P.O. Box 16, 6700 AA Wageningen, The Netherlands. E-mail: sun.zhongkui[at]wur.nl; juan.lopez-raez[at]wur.nl
3. UMR 5546 CNRS/Université Paul Sabatier, 24, chemin de Borde-Rouge, BP 42617, Auzeville 31326, Castanet-Tolosan, France. E-mail: rochange[at]scsv.ups-tlse.fr; becard[at]scsv.ups-tlse.fr
The strigolactones are signaling molecules that are used by the root parasitic broomrapes (Orobanche spp) and witchweeds (Striga spp) as well as the symbiotic arbuscular mycorrhizal (AM) fungi to detect the presence of their plant host. The requirements for such signaling molecules are that these compounds should be specifically indicative of the presence of a plant host. We are elucidating the biosynthetic origin of the strigolactones in several host plants of AM fungi as well as parasitic plants. This led to the discovery that the strigolactones are derived from the carotenoids - and should therefore be called apocarotenoids and not sesquiterpene lactones - and as such are quite "plant-specific". Considering the dual signaling role of the strigolactones it is interesting that there is an interaction between AM fungi and parasitic plants through the host plant, resulting in reduced parasitism by Striga hermonthica on sorghum and maize that are colonized by AM fungi. We will discuss the evidence that this interaction is mediated through the production of strigolactones. Also the further elucidation of the strigolactone biosynthetic pathway, initially focusing on the first dedicated step that is probably catalyzed by a carotenoid cleavage dioxygenase will be discussed. We are cloning genes from the pathway to make transgenic plants with altered strigolactone biosynthesis. These plants will be a great tool to study the importance of these signaling molecules for the interaction of plants with friends as well as enemies.
Cameron, DD (1), Keith, AM (2), and Seel, WE (3)
Rhinanthus minor as an Ecosystem Engineer: Understanding the Mechanistic Basis of Parasitic Plant-Induced Changes in Community Structure.
1. Department of Animal and Plant Sciences, University of Sheffield, UK.
2. Centre for Ecology and Hydrology - Banchory, UK
3. School of Biological Sciences, University of Aberdeen, UK
The root hemiparasite Rhinanthus minor, can suppress the abundance of grasses whilst promoting forbs in grassland communities, however, the outcome of its introduction is highly variable. We investigated the factors influencing this variability by studying the mechanisms through which the parasite acts to facilitate changes in community structure. Field manipulations confirmed that R. minor, suppresses the growth of grasses and whilst promoting that of forbs in the first growing season of a newly sown meadow. In contrast the removal of R. minor from mature meadow plots did not influence their floristic composition. In pot-based studies the parasite was highly damaging to grasses but had no significant effect on forbs although it did attach to them. Moreover, the parasite performed worst in terms of growth and photosynthesis when attached to forbs, even compared with unattached individuals. We hypothesized that forbs express resistant to the parasite. Tracer experiments using 1N-nitrate supplied to the host confirmed this as the parasite abstracts more nutrients from grasses than from forbs. Histological studies established that all of the forbs possessed successful resistance mechanisms to haustorial penetration of host vascular tissues whilst no successful resistance was observed in the grasses. Two different resistance mechanisms were observed in the forbs; hypersensitive cell-death and host lignification at the host-parasite interface. Our results establish that differential host resistance underlies the community level effects of R. minor as forbs possess a resistance capacity that other potential hosts do not, consequently the parasite moderates intra-specific competition within grassland communities promoting forb abundance.
Castillejo, MA (1), Maldonado, AM (1), Dumas-Gaudot, E (2), Pérez de Luque, A (3), Rubiales, D (3), and Jorr’n, J (1)
Differential expression proteomics to investigate responses and resistance to Orobanche crenata in legumes
1. Department of Biochemistry and Molecular Biology, University of Cordoba, C—rdoba, Spain. E-mail (corresponding author): bf1jonoj[at]uco.es
2. UMR 1088 INRA/CNRS/UB (Plant-Microbe Environment) INRA-CMSE, Dijon, Cedex, France
3. IAS-CSIC, Cordoba, Spain.
In order to study the plant response to parasitic plants and the molecular basis of the resistance we have used a proteomic approach. The root proteome of two accessions of the model legume Medicago truncatula and crop pea displaying differences in their resistance phenotype, in control as well as in infected plants have been compared. We report quantitative and qualitative differences in the two-dimensional gel electrophoresis (2-DE) maps of different plant genotypes and plant subjected to different treatments (control, non-infected, and infected). Differential spots were successfully identified by peptide mass fingerprinting (PMF) following MALDI-TOF mass spectrometry. Many of the proteins identified that show significant differences between genotypes and after parasitic infection belong to the functional category of photosynthesis and energetic metabolism, and defense and stress-related proteins. Data will be presented and discussed in terms of plant spp. and genotype common and differential responses, as well as compared with those previously obtained by using classical biochemical and transcriptomic approaches. Data have been published or submitted (Castillejo et al., 2004. Phytochemistry 65: 1817; Jorrin et al., 2006. Euphytica 147: 37; Rossignol et al., 2006. Proteomics 6: 5529; Rispail et al., 2007. New Phytologist 173: 703; Castillejo et al., 2007. Plant Physiology (submitted).
Chachalis, D (1), and Murdoch, AJ (2)
Potential Use of Nijmegen-1 and Smoke Water Solutions to Deplete Orobanche ramosa Seed Banks in Greece
2. Department of Agriculture, The University of Reading, Earley Gate, P.O. Box 237, Reading RG6 6AR, UK E-mail: a.j.murdoch[at]reading.ac.uk
Laboratory and field experiments were conducted to study the effect of using stimulants to deplete Orobanche ramosa seed banks. Germination stimulants tested in the laboratory were Nijmegen-1 (NE-1: 10-4, 10-6, 10-8 and 10-10 mol/L) and two smoke water (SW) solutions, ("Seed Starter" from Australia and a comparable solution produced by burning hay in Greece) were studied. SW concentrations tested were 100, 10, 1, 0.1 and 0.01% v/v aqueous solutions. In the field experiment, five treatments (10-5, 10-6, 10-8 mol/L of NE-1 respectively, 1% v/v local SW, and 10-5 mol/L of NE-1+ 1% v/v local SW) were tested in a tobacco field. The field was initially uninfected with Orobanche and 500-1000 O. ramosa seeds were placed at marked locations to which tobacco plants were subsequently transplanted. The field site was kept moist for a week to allow the seeds to precondition after which the stimulant solutions were sprayed using a backpack sprayer at 93.5L/ha spray volume and 207 kPa of pressure. Plots were then kept moist for two weeks to allow seeds to germinate and die before transplanting tobacco to each location. Additionally, in each plot at least 100 seeds were placed in nylon mesh packets at 2.5 cm depth. These packets were exhumed and germination was recorded. The non-germinated seeds on exhumation were placed in Petri-dish (1wk, 23¼C) with distilled water for further estimation of germinability of seeds. In the laboratory, 10-6 mol/Litre NE-1 induced 38% germination as did the standard 10-6 mol/Litre GR24. Lower and higher NE-1 concentrations exhibited much lower germination, at levels similar to water control (4% germination). The local SW stimulated 78% germination at 1% v/v concentration, higher than the "Seed Starter" SW (52%). At high concentrations, both SW strongly inhibited (less than 13%) germination. The "Seed Starter" SW at more diluted concentrations (0.1 and 0.01% v/v) exhibited a gradual decline of germination (45, 32% germination, respectively). In contrast, the local SW showed a 48% germination even at the lowest concentration (0.01%). Depletion of O. ramosa seeds, as recorded in the exhumed seed packets, was well over 50% with the optimum local SW treatment compared to 38% with 10-6 mol/L NE-1. There was little difference between the other treatments (max. depletion 32%). Some caution should be exercised as germination was incomplete at the time of exhumation and was allowed to continue in petri dishes moistened with water. Germination of O. ramosa seeds in situ in the soil was ½ to 1/3 of the total seed germination. The use of smoke and smoke water to stimulate germination in both laboratory and field is well-known for a wide range of species although very little work has been carried out on parasitic weeds. The potential of smoke water to deplete the Orobanche soil seed bank is therefore interesting and the implications of smoke water and other stimulants such as NE-1 to deplete O. ramosa seed banks before transplanting susceptible crops will be discussed.
Chiang, MY (1), Hsieh, YC (1), Yuan, CI (1), and Lin, FY (1)
Cuscuta Species in Taiwan: Molecular Differentiation and Related Findings
1. Taiwan Agricultural Chemicals and Toxic Substances Research Institute, 11 Kuang Ming Road, Wufeng, Taichung, Taiwan 413. E-mail: Chiang myc[at]tactri.gov.tw, Hsieh ych[at]tactri.gov.tw, Yuan yci[at]tactri.gov.tw, Lin mtlin[at]tactri.gov.tw
Cuscuta in Taiwan consists of mainly three taxa: C. japonica, C. japonica var. formosana, and C. campestris. C. japonica and C. japonica var. fomosana parasitize woody hosts of lowland and mountain areas, respectively. C. campastris is predominantly associated with herbaceous hosts of lowland habitats. Additionally, C. chinense and C. australis have been documented, but the former is rare and the later has been noted as mis-identification of C. campestris. We used different PCR methods to study samples collected from widespread areas. ISSR (Inter Simple Repeat) markers could clearly differentiated morphologically diversified taxa of Cuscuta. ITS (Internal Transcribed Spacer) data revealed that C. campestris from different sites were relatively homogenous with similarity higher than 98%. However, ITS sequences among populations of C. japonica or C. japonica var. formosana were abnormally variable (similarity could be lower than 80%) for the species level. Our further investigations on ITS led to interesting findings on possible DNA transfer between C. japonica complex and their hosts.
De Mol, M (1), and Heller, A (1)
Sap Flow from Host to Mistletoe: an Anatomical Approach
1. Institute of Botany, University of Hohenheim, Garbenstrasse 30, 70599 Stuttgart, Germany. E-mail: mdemol[at]uni-hohenheim.de, heller[at]uni-hohenheim.de
The mistletoe Viscum album L. is a hemiparasitic flowering plant. It is (partially) carbon autotrophic, but obtains water and nutrients by tapping into the wood of the host. Classical light microscopical methods and high-resolution 3D X-ray computed tomography were used on poplar (Populus x canadensis Moench, Salicaceae) infected with mistletoe (Viscum album L., Viscaceae) to understand water flow and development of the endophytic system. Direct vessel-vessel connections at the interface host-mistletoe ensure mass water and nutrient transport to the parasite. Almost every host vessel bordering the mistletoe haustorium had a simple perforation that directly connected them with the xylary elements of the parasite. The presence of the parasite showed a high and well directed influence not only on the quantity of wood produced by the host (hypertrophy), but also on the grain of the host wood. The mistletoe seems to direct actively the sap flow of the host towards its haustoria. In this respect, dimensions and morphology of the haustoria and host-mistletoe interface are of significant importance. The broad parasite vessels near the interface transport the sap to xylary elements with a smaller diameter, which conduct the water towards the cortical strands and the aerial parts of the mistletoe. Could this transition to narrower xylem elements pose a significant resistance for water conduction?
dePamphilis, C (1), McNeal, J (2), and Zhang, Y (1)
Genome Evolution in Parasitic Plants: New Genomes, Surprising Findings
1. Department of Biology, Penn State University, University Park, PA, 16802
2. Department of Plant Biology, University of Georgia, Athens, GA, 30602
Although most species of flowering plants are free-living and fully photosynthetic about 1% of plant species are direct parasites of photosynthetic plants, and as a result lead partly to fully heterotrophic lifestyles. How parasitism originated and how their genomes evolve under dramatically altered evolutionary constraints are fundamental problems. Here we report on the sequences of plastid genomes from two Cuscuta and one Pholisma (Lennoaceae) species, and compare them to Epifagus (Orobanchaceae), collectively representing three independent heterotrophic lineages. These genomes show unexpected retention of photosynthetic genes and pathways in some entirely heterotrophic species and almost perfect parallel reduction in gene content in others. There is even the possibility that some non-photosynthetic plants have lost their plastid genomes entirely. While plastid and mitochondrial genomes are now focus of intensive study in parasitic plants, nuclear genomes of parasites remain relatively understudied due to their large size and complexity. Large-scale EST studies and gene sequencing of parasites and parasite-host interactions are now feasible targets for research. These will provide crucial data for understanding parasite biology and developing effective strategies for parasite control.
Dewaele, D (1), Elsen, A (1), and Obiudoh, CA (2)
A Study of Biodiversity of African Radopholus Similis In Uganda.
1. Department of Biosystems, Kasteelpark Arenberg 13 - Bus 02455, B - 3001 Heverlee, Katholic Universiteit, Leuven, Belgium. E-mail: dirk.dewaele[at]biw.kuleuven.be, annemie.elsen[at]biw.kuleuven.be
2. Biology Department, University Gent, K.L. Ledeganckstraat 35, B-9000 Gent, Belgium. E-mail: cobiudoh[at]yahoo.com
The main problem that nematologist are facing during screening for nematode resistance is the variability in the reproduction of different R. similis populations. Assessment of this variability will be highly useful to banana breeding programs for incorporating resistance to nematodes. The reproductive fitness of four Radopholus similis populations (Ikulwe, Sendusu, Mukono and Mbarara) were studied on carrot disc (in vitro) and on plantain cultivar (in vivo) Obino l Ewai, as a function of time, inoculum densities and its pathogenicity on plant. In the first experiment, the reproductive fitness of the isolates was followed during two, four, six and ten weeks after inoculation. There were significantly (p<0.05) differences in the reproductive fitness of R. similis populations from Uganda as an effect of time. Increase in time increases the final nematode population. The experiment to test the effect of different inoculum density with respect to the reproduction of these populations on the carrot discs shows no significant different in their rate of reproduction at 6 weeks after inoculation. Regarding reproduction and pathogenicity of R. similis on plants, no definite conclusion can be drawn from the result obtained.
de Zélicourt, A (1), Letousey, P (2), Thoiron, S (1), Montiel, G (1), Simier, P (1), and Delavault, P (1)
Molecular analysis of resistance mechanisms to Orobanche cumana in sunflower
1. Université de Nantes, Nantes Atlantique Universités, Laboratoire de Biologie et Pathologie Végétales, EA1157, 2 rue de la Houssini�re, BP 92208, Nantes, F-44000 France. Axel.De-Julien-De-Zelicourt[at]univ-nantes.fr, philippe.delavault[at]univ-nantes.fr
2. Université de Reims, Laboratoire de Stress, Défenses et Reproduction des Plantes, UFR Sciences, BP 1039, Reims F-51687 Cedex 2, France
In sunflower, resistance to Orobanche cumana is characterized by a low number of parasite attachments and a confinement of the parasite in host tissues leading to its necrosis. To help understand what are the mechanisms governing such resistance, a molecular approach was employed during both early and late responses of susceptible (2603) and resistant (LR1) sunflowers infected by O. cumana. The expression patterns of defense-related genes were investigated. The resistant genotype exhibited a stronger overall defense response against O. cumana than the susceptible one, involving preferentially marker genes of JA and SA pathways. Among them, HaDef1 (defensin), appeared to be characteristic of the LR1 resistance. Plant defensins are small basic peptides of 5-10 kDa and most of them exhibit antifungal activity. In LR1, among the three defensin encoding cDNA identified, only HaDef1 presented a preferential root expression pattern and was induced upon infection by the root parasitic plant O. cumana few days before necrosis occurred. A 5.8 kDa recombinant peptide, Ha-DEF1, was produced in E. coli. Investigation of in vitro antifungal activity of Ha-DEF1 showed a strong growth inhibition of Saccharomyces cerevisiae and a morphogenetic activity on Alternaria brassicicola germ tube development. Bioassays also revealed that Ha-DEF1 rapidly induced cell death at the radicle apex of Orobanche seedlings but not of another parasitic plant, Striga hermonthica, nor of Arabidopsis thaliana. These results demonstrate for the first time a lethal effect of defensins on plant cells. The putative mode of action of defensin in Orobanche cell death and its possible involvement in sunflower resistance will be discussed.
Dhanapal, GN(1), Borg, SJ ter (2), and Struik, PC(3)
Integrated Management of Broomrape in India
1. Department of Agronomy, University of Agricultural Sciences, GKVK Campus, Bangalore-560 065, India. E-mail: gndhanapal[at]yahoo.co.in
2. Hamelakkerlaan, 11, 6703 EE, Wageningen, The Netherlands. E-mail: Siny.terBorg[at]staf.TON.WAU.NL
3. Plant Sciences,Crop and Weed Ecology, Wageningen Agricultural University, Haarweg 333, 6709 RZ, Wageningen, The Netherlands. E-mail: Paul.Struik[at]wur.nl
Bidi tobacco is a non-Virginia tobacco, being cultivated in Nipani (India) for the 45 years under rainfed conditions. In India, Orobanche cernua is the most pernicious parasitic weed in tobacco cultivation. The severity of broomrape problem is increasing because of mono-cropping of tobacco and hand weeding is the only practice to control it. Among different chemicals tested GR 24 induced 58% germination of broomrape seeds under laboratory conditions. The positive interaction between GR 24 (I.0 ppm) and the root exudates of few crops deserves further attention. In trap crop field experiment, sunhemp and greengram crops reduced broomrape population by 68% and increased tobacco yields by 45% at 90 days after transplanting (DAT). Glyphosate and Imazaquin at 0.50 kg ai/ha and 0.01 kg ai/ha, respectively, reduced the number and dry weight of broomrape spikes. However, we suggest the following integrated cultural and chemical control approaches to obtain higher tobacco yields and minimize broomrape population in the soil for tobacco areas in Nipani and areas of similar conditions in India: (1) Grow trap crops (sunhemp/greengram) in the early spring and incorporate in situ at 45 days after sowing; (2) Transplant tobacco after 15-20 days; (3) Take up general hand weeding within 45 DAT; (4) Apply glyphosate at 60 DAT at 0.50 kg at ai/ha (or less); (5) Remove the remaining few broomrapes spikes by hands or apply plant oils to prevent seed formation. Also a cropping system with trap crop - short fallow - tobacco is an ideal practice to reduce the broomrape seed inoculumÕs potential in the soil.
Draie, R (1), Pouvreau, JB (1), Véronési, C (1), Théodet, C (1), Thoiron, S (1), Delavault, P (1) and Simier, P (1)
The Sucrose-Degrading Enzymes in Orobanche ramosa. Characterization and Involvement in Growth, Cell Wall Synthesis and Starch Accumulation.
1. Université de Nantes, Nantes-Atlantique Universités, Laboratoire de Biologie et Pathologie Végétales, EA 1157, UFR Sciences et Techniques, 2 rue de la Houssinire F44322 Nantes, France. ridadraie[at]hotmail.com, jean-bernard.pouvreau[at]univ-nantes.fr, christophe.veronesi[at]univ-nantes.fr, catherine.theodet[at]univ-nantes.fr, severine.thoiron[at]univ-nantes.fr, philippe.delavault[at]univ-nantes.fr, philippe.simier[at]univ-nantes.fr.
O. ramosa is an obligate parasite of major crops such as tobacco, tomato, oil seed rape and hemp. It has been known for more than two decades that the host-derived sucrose supports parasite growth. Nevertheless, sucrose metabolism in the parasite remains to be elucidated. We have initiated studies aiming at characterizing the molecular components, such as cell wall invertase (CWI), vacuolar invertase (VI), neutral/alkaline invertase (NI) and sucrose synthase (SuSy), involved in sucrose mobilization in Orobanche ramosa growing on tomato roots. Our first data show that tubercles display an equilibrated VI / NI ratio while this ratio is stronger in the growing subterranean stems due to a specific increase in VI activity. This reflects the key role of this enzyme during sucrose utilization in the growing stem where cell expansion occurs through vacuolar hexose and mannitol accumulation. The VI enzyme was purified using affinity and gel filtration chromatography. Only one isoenzyme was detected in stems, and the native form shows a pI of 3.8 and a molecular mass of 98 7 kDa. Protein sequencing is in progress. CWI activity is constant to a basal level in tubercles and stems. In contrast, tubercles display a significant SuSy activity. Using antibodies raised against faba bean SuSy, we show that this enzyme is strongly associated to tracheids and amyloplasts contained in parenchyma cells. It suggests that in tubercles SuSy is involved in the sucrose mobilization required for cell wall polysaccharide synthesis in tracheids and for starch accumulation in parenchyma cells.
Dubé, M-P (1), and Belzile, FJ (1)
Genetic variability among five races of Striga gesnerioides (Willd.) Vatke detected by ISSR, AFLP and cpSSR analysis.
1. Departement de phytologie, Université Laval, Québec City, QC G1K 7P4, Canada.
Striga gesnerioides (Willd.) Vatke is an obligate root parasite of several dicotyledonous species including cowpea (Vigna unguiculata (L.) Walp.), an important legume crop of the semi-arid regions of West Africa. Based on host-parasite interactions in the field, various races of S. gesnerioides attacking cowpea have been identified. In this study, we investigated the genetic variability within and between 44 populations of five of the previously recognized races of the parasite present in West Africa. Three different types of molecular markers were used on up to 10 individuals from each population. ISSR (inter-simple sequence repeat) markers showed no genetic variability within populations. The variability between the populations was also extremely low and did not allow discrimination of the five races. A few populations were more closely related (notably two populations from Togo), but no geographical or "racial" clustering could be seen. Further work with ISSR and AFLP (amplified fragment length polymorphism) markers is in progress to improve the accuracy of the analysis. Finally, we used cpSSR (chloroplastic simple sequence repeat) markers as these have been shown, in many studies, to reveal greater amounts of polymorphism at the intraspecific level. A total of 34 cpSSR primer pairs from various species were used, 26 of which produced amplicons in Striga. Absolutely no polymorphism was observed with cpSSR markers emphasizing that despite a large geographical distribution, very low genetic variability can be found in the different populations of S. gesnerioides. This may be due in part to the autogamous mode of reproduction of the parasite.
Dunlavey, R (1), Logan, BA (1) and Reblin, JS (1)
The Influence of Arceuthobium pusillum Infection on the Hydraulic Architecture of White Spruce Stems
1. Department of Biology, Bowdoin College, Brunswick, ME 04011USA
E-mail: rdunlave[at]bowdoin.edu, blogan[at]bowdoin.edu, jreblin[at]bowdoin.edu
Arceuthobium pusillum (eastern dwarf mistletoe) is an aerial hemiparasitic angiosperm whose primary hosts are white spruce (Picea glauca), red spruce (Picea rubens) and black spruce (Picea mariana). Although the biology, ecology, and population genetics of Arceuthobium species have been examined in some depth, comparatively less is known about the impacts of Arceuthobium infection on the physiological performance of their hosts. Arceuthobium infection is characterized by the establishment of an endophytic system that taps directly into host xylem and phloem, through which the parasite withdraws all of the water, mineral nutrients and much of the fixed carbon that it needs to support its growth. Along the coast of Maine, Arceuthobium pusillum infection causes severe mortality in white spruce stands. We investigated the impact of Arceuthobium pusillum infection on white spruce stem hydraulic conductivity. Infection reduced white spruce stemsÕ capacity to deliver water (specific conductivity) by more than 25%. This perturbation may explain the dramatic reduction (>40%) in needle size distal to infection. Needle size reductions may offset reductions in hydraulic conductivity and water use by Arceuthobium to restore the balance between host leaf area and the capacity to transport water through stems. As a result, infection had no significant impact on a stemÕs capacity to deliver water when expressed on the basis of leaf area distal to infection (leaf specific conductivity). Furthermore, we found that infection did not have an impact on the occurrence of cavitation in white spruce stems.
Dzomeku, IK (1), and Murdoch, AJ (2)
Studies on Seed Dormancy, Germination and Seedling Emergence of Striga Hermonthica
1 Department of Agronomy, Faculty of Agriculture, University of Development Studies, P.O. Box TL 1882. Nyankpala, Tamale, Ghana.
2. The University of Reading, School of Agriculture, Seed Science Laboratory. P. O. Box 236. Reading UK.
This paper represents the first attempt to apply a conditioning model for parasitic weeds to seeds in soil in the glasshouse. The previous models developed for Striga hermonthica and for three Orobanche species were only applied empirically and were not validated on independent data sets. The results indicate that S. hermonthica seeds recovered from eight soil environments of different drought and urea treatments, attained germination within 14-28 days and these optimum periods were similar to predictions based on the in vitro model, Once the seeds have been in imbibed storage in the soil for more than about 28 days in this experiment, induction of secondary dormancy increased but gradually, leading to a slow decrease in germination over a period of 91 days which in most environments did not terminate in zero germination. After 119 days of conditioning in the soil, germination percentages remain significantly high compared to the model predictions. The implication of the present findings for the control of S. hermonthica was discussed.
Echevarr’a-Zome–o, S (1), Pérez-de-Luque, A (2), Jorr’n, J (1), and Maldonado, AM (1)
Histochemical analysis of defense responses involved in resistance of sunflower ( Helianthus annuus) to Orobanche cumana
1. Agricultural and Plant Biochemistry Research Group, Dpt. of Biochemistry and Molecular Biology, University of Cordoba. Cordoba, Spain, E-mail: g72eczos[at]uco.es; bf1jonoj[at]uco.es; bb2maala[at]uco.es
2. IFAPA-CICE (Junta de Andalucia), CIFA, çrea de Mejora y Biotecnolog’a, C—rdoba, Spain.
Sunflower broomrape (Orobanche cumana Wallr.) is considered as one of the major constraints for sunflower production in Mediterranean areas1. Breeding for resistance is regarded as the most effective and environmental friendly solution to control this parasite. However, the existing sources of genetic resistance are defeated by emergence of new more virulent races of the parasite.
In this work we have analysed the interaction between sunflower and O. cumana in order to get insights into the mechanisms involved in resistance. The interaction between O. cumana and two sunflower genotypes showing different behavior against the race F of O. cumana, HE-39998 (susceptible) and HE-39999 (resistant), were monitored by pot and Petri dish bioassays. Then, using histochemical procedures and microscopic observations, compatible and incompatible interactions were compared and several defense responses involved in resistance were identified2. Suberization and protein cross-linking at the cell wall were observed in the resistant sunflower cells in contact with the parasite, preventing parasite penetration and connection to the host vascular system. In addition, fluorescence and confocal laser microscopy observations revealed accumulation of phenolic compounds during the incompatible interaction, which is in agreement with these metabolites playing a defensive role during H. annuus - O. cumana interaction3.
et al. (1998) Helia
2. Echevarr’a-Zome–o, et al. (2006) Journal of Experimental Botany, 57: 4189.
3. Serghini, et al. (2001) Journal of Experimental Botany 52: 2227.
Eizenberg, H (1), Ephrath, J (2), Lande, T (1), Achdari, G (1), and Hershenhorn, J (1)
Temporal Thermal and Special Model for Orobanche Management
1. Agricultural Research Organization, Newe-Ya'ar Research Center, Ramat Yishay, Israel. eizenber[at]volcani.agri.gov.il
2. Wyler Department of Dryland Agriculture, Jacob Blaustein Institutes for Desert Research, Sede-Boqer, Ben-Gurion University of the Negev, Israel.
The overall goal of our study is to develop a decision support system for Orobanche control base on spatial and temporal sub-models. a) Temporal model: in previous studies, a mathematically relations between temperature and the parasitism process of O. aegyptiaca, O. minor and O. cumana, in tomato, red clover, and sunflower, respectively, was shown. A Growing Degree Days (GDD) model was developed to predict Orobanche parasitism in these crops. Using a sigmoid function allows us to predict the timing of the various Orobanche spp. developmental including subsurface stages. Herbicidal control of Orobanche was achieved in tomato, red clover, and sunflower using ALS inhibitors. The most effective control was achieved in the subsurface parasitism phase. Optimized chemical control is achieved when minimal herbicide rates are applied to the host at the most susceptible stage of the parasite. Herbicide application timing is based on the GDD model mentioned above. Recently, the option of in-situ monitoring sub-surface parasitism was introduced by using the minirhizotron camera. This is a non-destructive tool for detecting and monitoring parasitism over time. The minirhizotron technology is essential for verifying the herbicide rate models. This will allow making proper decisions regarding to herbicide application timing. b) Remote sensing approach was used for modeling the spatial distribution of O. aegyptiaca in tomato and in dill fields. IR, NIR and RGB aerial images were taken from satellite and from air for tomato and parsley fields infected with O. aegyptiaca. Orobanche aegyptiaca could be partially detected only by RGB aerial images.
Elzein, A (1), Fen, B (2), Kroschel, J (3), Marley, P (4), and Cadisch, G (1)
Synergy Between Striga- Mycoherbicides "Fusarium oxysporum f.sp. strigae" and Resistant Cultivars Under Field Conditions: Step Towards Integrated Striga Control in Africa
1. Institute for Plant production and Agroecology in the Tropics and Subtropics (380), University of Hohenheim, D-70593, Stuttgart, Germany. Email: gasim[at]uni-hohenheim.de, cadisch[at]uni-hohenheim.de.
2. International Institute of Tropical Agriculture (IITA), 08 BP 0932 Tri Postal, Cotonou, Republic of Benin. E-mail: f.beed[at]iita-uganda.org.
3. Integrated Crop Management Division, International Potato Center (CIP), Av. La Molina 1895, Apartado 1558, Lima 12, Peru. E-mail: j.kroschel[at]cgiar.org.
4. Department of Crop Protection, Faculty of Agriculture/Institute for Agricultural Research, Ahmadu Bello University, Samaru, Zaria, Nigeria. E-mail: psmarley[at]yahoo.co.uk.
Striga spp. are important constraints in cereal and legume production in semi-arid tropical Africa. An integrated approach, in which biocontrol represents an important component, appears to be a promising strategy for reducing Striga infestation. Fusarium oxysporum f.sp. strigae (isolates Foxy 2 & PSM197) are potential, highly host specific mycoherbicides against S. hermonthica. For facilitating practical field application, our recent research focuses on the development of appropriate mycoherbicidal formulations and delivery systems. Hence, Pesta formulation made by encapsulating fungal inoculum in a matrix composed of durum wheat-flour, kaolin, and sucrose, was developed. Seed treatment technology for coating sorghum and maize seeds as an attractive option for further minimizing the inoculum amount and facilitating delivery of Striga-mycoherbicides was also provided. Integration of Pesta formulation and treated seeds containing Striga-mycoherbicides (Foxy 2 & PSM197) with Striga resistant and susceptible maize and sorghum cultivars under field conditions of West Africa was investigated. The combination Pesta granules or treated seeds and resistant maize and sorghum cultivars enhanced clearly both mycoherbicides efficacy, and showed the strongest suppressive effect on Striga compared to susceptible cultivars. The difference between the resistant and the susceptible cultivars was stronger for maize than for sorghum. On average (i.e. the average effect of both isolates), they reduced the number of emerged Striga plants per plot by 96% or 89% when the two isolates formulated as Pesta granules or delivered as coated seeds, respectively, and combined with the resistant maize cultivars compared with the control of the susceptible cultivars. On the other hand, the respective reductions when the two isolates integrated with the susceptible maize cultivars were 85 %, and 21%. Improvement in maize and sorghum performances (height, grain yield, stalks dry weight, etc.) was recorded. Further, both mycoherbicides maintained excellent viability (shelf-life) on Pesta products and treated seeds after one year of storage which would be sufficient for their use under practical conditions of storage, handling and delivery. The suitability of Pesta and seed treatment technology for formulating and delivering Striga-mycoherbicides and their compatibility and synergy with Striga resistant cultivars, are highly relevant to the realization of an integrated Striga control approach adoptable and applicable by subsistence farmers in Africa.
Key words: Weed biological control, Mycoherbicide, Encapsulation, Seed coating, Integrated control, Fusarium oxysporum, Striga hermonthica, Striga-resistant cultivars, Sorghum bicolor, Zea mays
Elzein, A (1), Kroschel, J (2), Fen, B (3), Marley, P (4), and Cadisch, G (1)
Compatibility of Striga-Mycoherbicides with Fungicides Delivered Using Seed Treatment Technology and its Implication For Striga and Cereal Fungal Diseases Control
1. Institute for Plant production and Agroecology in the Tropics and Subtropics (380), University of Hohenheim, D-70593, Stuttgart, Germany E-mail: gasim[at]uni-hohenheim.de, cadisch[at]uni-hohenheim.de.
2. Integrated Crop Management Division, International Potato Center (CIP), Av. La Molina 1895, Apartado 1558, Lima 12, Peru. Email: j.kroschel[at]cgiar.org).
3. International Institute of Tropical Agriculture (IITA), 08 BP 0932 Tri Postal, Cotonou,Republic of Benin. E-mail: f.beed[at]iita-uganda.org.
4. Department of Crop Protection, Faculty of Agriculture/Institute for Agricultural Research, Ahmadu Bello University, Samaru, Zaria, Nigeria. E-mail: psmarley[at]yahoo.co.uk.
Root parasitic weeds of the genus Striga and fungal diseases constitute a major biotic constraint to staple food production in Africa, and consequently aggravate hunger and poverty. With the aim of improving sorghum and maize performance and yield, an investigation on the possibility of delivering the potential Striga-mycoherbicides (Foxy 2 & PSM197) and some selected fungicides using seed treatment technology to control simultaneously Striga and sorghum and maize fungal diseases was made for the first time. Sorghum film-coated seeds with different application rates (dosages) of Apron XL and Ridomil Gold in combination with the mycohericides Foxy 2 and PSM197 and different coating adhesives were used. The effects of Apron XL and Ridomil Gold fungicides on growth and sporulation of the two isolates was examined by growing the film-coated sorghum seeds on PDA media. Delivering of the fungicides Apron XL and Ridomil with Striga-mycoherbicides Foxy 2 and PSM197 using seed treatment technology did not interfere with seed coating process as well as with the initial survival of fungal isolates on coated sorghum seeds. Apron XL clearly enhanced the growth, sporulation and viability of both isolates, indicating strong compatibility with Striga- mycoherbicides. However, Ridomil Gold was not compatible on PDA medium. Under filed conditions of West Africa, the integration of fungicide Apron XL (at a rate of 0.5 ml /kg of seeds) with Striga-mycoherbicides (Foxy2 & PSM197) and resistant maize cultivars using seed treatment technology and Arabic gum as adhesive showed significant reduction in Striga emergence by 81% and 90% compared to the respective resistant and susceptible controls. Improved performance of maize treated with Striga-mycoherbicides and fungicide was recorded. The compatibility between Striga-mycoherbicides and Apron XL fungicide has significant implication for controlling simultaneously Striga and sorghum and maize fungal diseases and improving crops performance and yield.
Fan, ZW (1), Buschmann, H (2), Shen, YD (1), Lu, Y (1), and Sauerborn, J (2)
Induced Host Resistance as a Control Method for Parasitic Weeds
1. Environment and Plant Protection Institute, Chinese Academy of Tropical Agricultural Sciences; Key Laboratory for Pest Detection and Monitor of Tropical Agriculture of Hainan Province, Hainan 571737, China
2. Institute of Plant Production and Agroecology in the Tropics and Subtropics, University of Hohenheim, Stuttgart 70593, Germany
Parasitic weeds restrict crop production in many countries. Plant induced resistance is against not only pathogens and herbivores, but also parasitic weeds. Induced resistance against parasitic weeds has been demonstrated in the associations of sunflower-Orobanche cumana, tobacco/hemp-O. ramosa and pea-O. crenata under greenhouse conditions and/or in the field. Plant activators include biotic and abiotic agents. Host plants underlay systemic acquired resistance (SAR) or induced systemic resistance (ISR) pathway against parasitic weeds. Induced resistance should be integrated in the parasitic weed management systems. This paper reviews the history and development, pathway and mechanism, as well as prospect and outlook of plant induced resistance on the control of parasitic weeds.
Fernández-Aparicio, M (1), Pérez-de-Luque, A (2), Sillero, JC (2) and Rubiales, D (1)
Yield increase in oat-faba bean intercrops under heavy Orobanche crenata infections.
1. CSIC, Instituto de Agricultura Sostenible, Apdo. 4084, 14080 C—rdoba, Spain. E-mail: monfapru[at]yahoo.com, ge2ruozd[at]uco.es
2. IFAPA Centro "Alameda del Obispo", Apdo 3092, 14080 C—rdoba, Spain. E-mail: bb2pelua[at]uco.es, josefa.sillero.ext[at]juntadeandalucia.es
Orobanche crenata (crenata broomrape) causes severe damage on legumes. Several cultural, biological, and chemical strategies have been suggested but none is completely successful or practicable in low input farming systems. We showed previously that broomrape infection on legumes is reduced in intercrops with oat. In the present experiment we studied the effect of broomrape reduction due to oat-faba bean intercrops on faba bean and broomrape biological dry matter (BDM). The assay was conducted in an infested experimental field in C—rdoba, Spain in organic conditions. Susceptible faba bean cv. "Prothabon" was grown as sole crop and mixed with oat cv. "Cory" in 50% replacement model intercrop. Crops were laid out on plots (1.5x8 m2) in a complete randomized block design with three replicates. The high Land Equivalent Ratio value (LER=1.3) achieved shows that environmental sources for oat-faba bean growth are used on average 30% more efficiently in the intercrops than in the respective sole crops due to a) the degree of resource complementarity of faba bean-oat system in absence of any fertilization and b) the reduction of crenata broomrape attached per faba bean plant due to the inhibitory effect of oat. Faba bean BDM was 928 g/m2 in sole crop and 666 g/m2 in intercrop. Broomrape BDM was reduced from 193 g/m2 to 42 g/m2 due to intercrop, reducing proportionally the number of seeds laid in soil.
Fernández-Aparicio, M (1), Pérez-de-Luque, A (2), and Rubiales, D (1)
Response of Medicago truncatula Accessions to Various Species of Orobanche
1. CSIC, Instituto de Agricultura Sostenible, 14080 C—rdoba, Apdo. 4084, Spain. monfapru[at]yahoo.com, ge2ruozd[at]uco.es.
2. IFAPA-CICE, "Alameda del Obispo", 14080 C—rdoba, Apdo. 3092, Spain. bb2pelua[at]uco.es
There is increasing interest in the legume species Medicago truncatula as a model in genomic studies. Genotypic variation for the mechanisms of resistance was found between M. truncatula accessions with an accession highly resistant and another highly susceptible to O. aegyptiaca, O. foetida var broteri and O. ramosa. Similar variation, but in reverse, was observed with O. nana. In vitro studies showed that M. truncatula can induce high levels of O. aegyptiaca, O. foetida var broteri, O. nana, O. minor and O. ramosa seed germination, but rather low levels of O. cumana, O. crinita and O. crenata. Differences in germination level among accessions were highly significant. Accessions also significantly varied in the penetration response to O. aegyptiaca, O. foetida var broteri, O. ramosa and O. nana. Increasing the germination level on O. cumana, O. aegyptiaca, O. ramosa and O. minor through applications of the synthetic germination stimulant GR24 did not result in increased infection. However, infection by O. nana increased markedly in the resistant accession. GR24 was no effective inducing germinating O. crinita, O. foetida var broteri and O. foetida var foetida seeds. The variation observed for induction of germination of these species by M. truncatula and of subsequent attachment will be useful to isolating and characterising genes involved in early stages of Orobanche - host plant interaction and for the study of the biosynthetic pathways of production for germination stimulants.
Fernández-Aparicio, M (1), Flores, F (2), Pérez-de-Luque, A (3) and Rubiales, D (1)
Yield losses in pea as a function of Orobanche crenata levels of infection.
1. CSIC, Instituto de Agricultura Sostenible, 14080 C—rdoba, Apdo. 4084, Spain
E-mail: monfapru[at]yahoo.com, ge2ruozd[at]uco.es
2. Escuela Politécnica la Rábida, Universidad de Huelva, 21819 Palos de la Frontera, Spain
3. IFAPA Centro "Alameda del Obispo", Apdo 3092, 14080 C—rdoba, Spain
Reduction of biomass and seed yield and size were studied on pea (Pisum sativum L.) as a function of level of infection by crenata broomrape (Orobanche crenata Forsk). The susceptible pea cultivar "Messire" was sown in a distance between plants and rows of 0.5 meter in a highly but no homogeneously naturally infested plot, what allowed us to study yield components in pea plants with a variable level of infection, ranging from 0 to 21 emerged broomrapes per pea plant. Pea productivity was measured as dry total biomass (DMp), seed yield (SYp) and number of seeds (NSp) measured per pea plant. The infection level was studied per pea plant determining the number of emerged broomrapes (Nb) and parasitic dry matter (DMb) measured at harvest. The following models were used for the prediction of productivity losses. Dry total biomass of pea was reduced with infection, as a function of number of emerged broomrapes DMp = 8.66+15.04e-0.20*Nb (r2=0.64), or broomrape biomass, DMp = 8.38+16.23e-0.30*DMb (r2=0.63). Pea seed yield were influenced by the infection level, both by number of broomrapes SYp = -3.96 + (103.86/(6.14+Nb)) (r2=0.73) and broomrape biomass, SYp = -3.20+13.74e-0.12*DMp (r2=0.67). This reduced yield was due to a decrease of number of seeds per pea plant NS p = -2.30+54.98e-0.14*Np (r2=0.70) and NSp = -17.49+70.30e-0.11*DMb (r2=0.66)), whereas seed weight was not influenced by infection level.
Funk, H (1), Berg, S (2), Krupinska, K (2), Maier, U (1) and Krause, K (2,3)
Complete DNA Sequences of the Plastid Genomes of Two Parasitic Flowering Plant Species, Cuscuta reflexa and Cuscuta gronovii
1. Institute for Cell Biology, Philipps-University Marburg, 35032 Marburg, Germany. E-mail: helena.funk[at]staff.uni-marburg.de, maier[at]staff.uni-marburg.de
2. Institute of Botany, Plant Cell Biology, Christian-Albrechts-University, 24098 Kiel, Germany.
3. Present address: Institute for Biology, University of Troms, 9037 Troms, Norway.
We have sequenced the complete plastid chromosomes of two parasitic flowering plant species, Cuscuta reflexa and Cuscuta gronovii. Both species are capable of performing photosynthesis, though with different efficiencies. Together with the achlorophyllous E. virginiana, of which the plastid genome was already published over a decade ago, these species represent a progression series towards total dependency on the host plant. The plastid chromosome sizes were found to be larger than that of E. virginiana with 121.5 kbp and 86.7 kbp, respectively. Although the chromosome structure is similar to that of non-parasitic plants, a number of insertions, deletions (indels) and sequence inversions were found. Gene losses are more pronounced in C. gronovii than in C. reflexa, encompassing some photosynthetic genes as well as many regulatory genes. Transcription of the C. reflexa ptDNA resembles that of nonparasitic higher plants regarding promoter structure and transcription patterns but shows marked differences in the steady state RNA profiles. In C. gronovii, genes for the photosynthetic apparatus were retained while the rpo genes coding for the plastid-encoded RNA polymerase that is responsible for their transcription were lost. Concomitantly, adaptations within the plastid genome have occurred that enable transcription mediated exclusively by a nuclear-encoded plastid RNA polymerase. Moreover, C. gronovii is the first plant where a loss of the intron-encoded splicing factor MatK was observed. Thus, Cuscuta is an interesting model for the evolution of reduced organellar genomes.
Gharib, C(1), Haidar ,MA(1), Sleiman, FT(1) and Sidahmed, MM(1)
Germination and Viability of Cuscuta spp. (Dodder) Seeds after Digestion in Sheep Rumen
Studies were conducted to examine the effect of sheep rumen digestion on germination and viability of Cuscuta spp. seeds in comparison to non-parasitic weed seeds and two crops (barley and lentil). Seed samples were put in small monofilament nylon bags and placed in the plastic rumen of fistulated sheep for 1, 2, 3 and 4 days, respectively. Total percent germination (Germination + viability) of seeds four days after placement (DAP) in the rumen were 85% for Cuscuta spp., 31% for Convolvulus arvensis and 17% for Chenopodium album. Seeds of Lolium multiflorum and Raphanus raphanistrum died three DAP, while seeds of lentil and barley died one DAP. The results indicate that grazing sheep could be an important vector for carrying viable weed seeds, particularly Cuscuta spp. seeds, in their digestive system and depositing them with their feces in un-infested fields.
Gebeyehu, S (1), Belayneh, A (2) and Tesfamariam, M (3)
Parasitic Weeds in Ethiopia : Challenges to Resource Poor and Small Scale Farmers
1. Instiitut de recherche pour le development, IRD-Gene Trop,911 Av. DÕAgropolis, BP 64501,F34394 Montpellier, France. e-mail: seyoum.gebeyehu[at]mpl.ird.fr
2. Ambo Plant Protection Research Centre, P.O. Box 2003, Addis Ababa, Ethiopia . belay120[at]yahoo.com
3. Institute for Plant Diseases, University of Bonn, Nussallee 9, D-53115 Bonn, Germany tmekete[at]yahoo.com
Parasitic weeds, Striga hermonthica on sorghum, S. asiatica on maize, cuscuta on noug, orobache on tomato and faba bean, entailed extensive loss of crop land productivity in the farmlands of drought affected and food deficit small scale farmers in Ethiopia. Reports indicate that they flourish in conditions that characterize the poorest farming community (small plots, monocropping, lack of oxen and natural manure and lack of agricultural inputs) and once areas are infested, they exacerbate the problem of overall poverty and food insecurity by decreasing yield. These and other parasitic weeds have been recorded and in general incur an estimated yield loss of 5-100% resulting in an escalating food aid. In this article, major parasitic weeds of economic importance and factors found to influence their expansion are reviewed, their relationship with poverty is highlighted, control measures and a way forward to tackle the scourge of these weeds in crop production is suggested.
Goldwasser, Y (1), Yoneyama, K (2), Xie, X (2), and Yoneyama, K (2)
Identification of the Stimulants Produced by Arabidopsis thaliana Responsible for the Induction of Orobanche Seed Germination
1. R.H. Smith Institute of Plant Sciences & Genetics in Agriculture, Faculty of Agriculture, Food & Environmental Sciences, The Hebrew University of Jerusalem, Rehovot 76100, Israel
2. Weed Science Center, Utsunomiya University, 350 Mine-machi, Utsunomiya 321-8505, Japan. E-mail: yoneyama[at]cc.utsunomiya-u.ac.jp
The seeds of obligate root parasitic plants belonging to the Orobanchaceae require specific conditions for germination, including the unique requirement for induction by stimulants secreted by plant roots. In recent years a group of strigol-related natural stimulants from plant root exudates that induce root parasitic plant seed germination have been identified and termed as strigolactones. Strigolactones are abundant in plants from a wide range of botanical families, hosts and non-hosts of parasitic plants. In previous studies we have revealed that the model plant Arabidopsis thaliana induced germination and is susceptible to Orobanche aegyptiaca, Orobanche ramosa and Orobanche minor. The aim of the present study was to produce, extract, purify and analyze the strigolactone seed germination stimulants exuded by the roots of wild type A. thaliana that are responsible for the induction of Orobanche spp. seed germination. To produce A. thaliana root exudates, a novel hydroponics culture system was developed and exudates were collected on activated charcoal placed in the culture growth medium. Exudates were extracted from the activated charcoal with ethyl acetate and concentrated in vacuo. The crude extracts were analyzed using high performance liquid chromatography connected to tandem mass spectrometry. All chemical analyses were coupled with Orobanche spp. seed germination bioassays. The root exudates chemical analyses and accompanying bioassays revealed several strigolactones that are active in Orobanche spp. seed germination. Orobanchol was identified as a major Orobanche spp. seed germination inducer produced by A. thaliana. The final identification of other detected known and novel strigolactones is in progress.
Gunathilake, P (1), Tomilov, A (1), Tomilova, N (1), Fillapova, T (1) and Yoder, JI (1)
Macromolecular Trafficking from Host Plants into the Hemiparasitic Plant Triphysaria versicolor
1. Department of Plant Sciences, Mail Drop 3, University of California-Davis, Davis, California 95616-8780, USA E-mail: jiyoder[at]ucdavis.edu
Cross family transport of informational macromolecules such as mRNA, proteins and microRNAs and their significance in parasitism is poorly understood. Understanding how plants synthesize, transform and respond to these molecules will further our appreciation of host-parasite interactions and may lead to better strategies for vegetation management. However, a limitation has been the lack of transformation and assay systems for macromolecular trafficking in parasitic plants. We developed both in vivo and in vitro assay systems for studying macromolecule trafficking between the root parasite Triphysaria versicolorr and its plant hosts. Transgenic roots were obtained on non-transgenic Triphysaria plants by Agrobacterium rhizogenes mediated ex vitro root transformation. Transgenic roots were also obtained from transformed calli. Micropropagated roots maintained their ability to make haustoria. Recent work showed that RNAi can traffic from a lettuce host to in vitro cultured T. versicolor roots. Transgenic GUSPlus T. versicolor root cultures were attached to lettuce generating double stranded RNA for GUS. Histochemical staining and semi-quantitative RT-PCR showed the silencing of GUS gene in root tips after haustoria connection with lettuce. In order to determine whether silencing signals are translocated throughout the parasitic plant, we made transgenic Arabidopsis bearing dsRNA targeting the T. versicolor phytoene desaturase gene (PDS). The hypothesis is that Triphysaria leaves will be bleached when Triphysaria is attached to Arabidopsis with the T. versicolor PDS construct, but not when attached non-transformed hosts. The experiments to determine whether siRNA mediated gene silencing of T. versicolor PDS occurs via haustoria connection are underway and will be reported.
Haddad, A (1) and Pala, M (1)
Significance of Parasitic Weeds for Food Legumes in Syria
1. International Center for Agricultural Research in the Dry Areas, (ICARDA), Aleppo, Syria.
E-mail: a.haddad[at]cgiar.org, m.pala[at]cgiar.org
Parasitic weeds, especially Orobanche and to a lesser extent Cuscuta, have been major constraints for many crops in the Middle East, particularly legumes such as lentil, faba bean, and recently winter-sown chickpea. Losses due to parasitic weeds are usually poorly documented mainly due to misleading survey results based on the observations of the parasite in the field rather than on the seed bank in the soil. Extensive research on crop and weed management in Syria, including crop rotations, fertilizers and trap crops as cultural control practices have had no impact on Orobanche alleviation. Delayed planting date is the only cultural practice available to the farmer to reduce Orobanche infestation, but this practice also reduces crop yield potential. Breeding for Orobanche resistance has had only limited success, except with developed Egyptian faba bean varieties. Synthetic stimulants did not perform in vivo as they did in vitro due to calcareous soil, and did not either reduce the seed bank or the level of parasite infestation, Solar sterilization using second-hand plastic sheets is having an increasing role in reducing infestation levels of weeds, including Orobanche, and other pests, under greenhouse vegetable production in extensive farming of coastal regions of Syria. Chemical control of parasitic weeds by herbicide application in some crops appears promising; however, more research is needed to minimize crop injury and to widen the herbicide selectivity for up-scaling recommendations to other crops. Despite available recommendations for chemical control of parasitic weeds in faba bean, and recently in lentils, adoption by farmers is low due to lack of effective extension. While much has been learned about the evolution, physiology, genetics, and ecology of parasitic plants in the past few decades, economic crop losses remain unacceptably high in most countries of the Mediterranean region. Concerted efforts are needed to apply at farm level what is already known about parasitic weeds in food legumes.
Harrison, MJ (1)
The Arbuscular Mycorrhizal Symbiosis; Genomics Approaches to Dissect Development and Function
1. Boyce Thompson Institute for Plant Research, Cornell University, Tower Road, Ithaca, NY, 14853, USA. email:mjh78[at]cornell.edu
In natural ecosystems, most vascular flowering plants live in symbiosis with arbuscular mycorrhizal (AM) fungi. These mutually beneficial associations develop in the roots, where the fungus colonizes the cortex to obtain carbon from the plant. In addition to inhabiting the root, the fungus establishes hyphal networks in the soil, via which phosphorus and other mineral nutrients are transferred to the root. Thus, the symbiosis has a beneficial impact on plant health. Fossil evidence suggests that plants have been associated with AM fungi since they first colonized land and today, AM symbioses are found in ecosystems throughout the world. Development of the AM symbiosis involves signal exchange between the symbionts and this occurs prior to, and following, the physical interaction of the symbionts. Once inside the root, both the fungal hyphae and plant cells differentiate to create a specialized symbiotic interface, the arbuscule-cortical cell interface, over which nutrients are exchanged. Recent studies identified strigolactones as one of the pre-contact signals in the AM symbiosis indicating an overlap with plant-parasitic plant interactions1. It is possible that there are parallels in the later stages of the interactions also.
We are using a
AM fungus, Glomus
study the molecular events that underlie development and functioning of
symbiosis. By integrating transcriptional profiling information with
genetics approaches we have been able to identify plant genes whose
is essential for the AM symbiosis.
1. Akiyama, et al. (2005) Nature 435: 824-827.
Heller, A (1), Elzein, A (2), De Mol, M (1), Kroschel, J (3) and Cadisch, G (2)
Colonization of F. oxysporum f.sp. strigae (Foxy 2) on roots of sorghum plants and its implication for Striga control using a seed treatment delivery system: an anatomical study
1. Institute of Botany (210), University of Hohenheim, D-70593, Stuttgart, Germany
E-mail: heller[at]uni-hohenheim, mdemol[at]uni-hohenheim.
2. Institute for Plant production and Agroecology in the Tropics and Subtropics (380), University of Hohenheim, D-70593, Stuttgart, Germany
E-mail: gasim[at]uni-hohenheim.de, cadisch[at]uni-hohenheim.de.
3. Integrated Crop Management Division, International Potato Center (CIP), Av. La Molina 1895, Apartado 1558, Lima 12, Peru. E-mail: j.kroschel[at]cgiar.org.
The application of biocontrol agents by a seed-coating procedure is an attractive option for establishing the biocontrol agent in the rhizosphere, the infection zone of the root parasitic weed Striga and offers a simple delivery system. Fusarium oxysporum f.s. strigae (Foxy 2) showed promising potential in controlling Striga when applied as a film-coat on sorghum seeds. The ability of Foxy 2 to colonize the root system of sorghum seedlings that emerged from film-coated seeds, as a prerequisite, was proved by plating pieces of roots on PDA medium. In addition, anatomical investigations were performed to follow the colonization of sorghum roots by Foxy 2. The spreading of the mycelia were observed by using light microscopy 1, 2, 3 and 4 weeks after germination. Transmission electron microscopy was used to get more information about the interaction between Foxy 2 and the roots of sorghum. Foxy 2 acts as a pathogen to Striga but is non-pathogenic to other plants. Nevertheless, Foxy 2 was growing on the root surface and penetrating the roots of sorghum. Within 2 to 3 weeks it was slowly colonizing the whole cortical parenchyma of the root, but hyphae did not enter the vascular cylinder and kill the plants even after 4 weeks. On the contrary, Foxy 2 even seems to promote the growth of sorghum plants. This indicates that Foxy 2 met the criteria of being an effective mycoherbicide for controlling S. hermonthica using seed treatment technology.
Höniges, A (1), Ardelean, A (1), and Wegmann, K (1,2)
Ecological and Physiological Investigations on Orobanche Species in the Spontaneous Flora of Romania
1. Faculty of Natural Sciences, Vasile-Goldis-University Arad, Str. Rebreanu nr. 91-93, RO-310414 Arad, Romania
2. Center of Molecular Biology of Plants, University of Tuebingen, Auf der Morgenstelle 5, D-72076 Tuebingen, Germany. E-mail: a_hoeniges[at]yahoo.de Wegmann[at]uvvg.ro
In contrast to the few weedy species most Orobanche species have remained wild flowers in the spontaneous flora. We are examining the occurrence and distribution of non-weedy Orobanche species in Romania, the soil properties and climatic conditions required for conditioning Orobanche seeds and the germination stimulants exuded by host plants (e.g., low or sufficient germination stimulants). The associated flora around each Orobanche spike was recorded and root exudates of the associated plants were tested for allelopathic effects (e.g., germination inhibition or inhibition of radicle exoenzymes required for penetrating into the host root). We are also testing possible reasons for low viable seed production or loss of seed by insects or fungi. The obtained results will be compared with the conditions in Baden-WŸrttemberg, Southern Germany, where most of the Romanian Orobanche species occur also in limited populations. The results will contribute to understanding the ecosystems in which non-weedy Orobanche species grow. They may also provide information on the conditions under which Orobanche species may turn into weedy forms when ecological conditions change. Moreover, they should provide a basis for fostering rare Orobanche species in Botanical Gardens for the future. Methodological approaches and observations in Romania during the past two years will be presented.
Kaldenhoff, RWE (1)
Molecular Events During Cuscuta Infection
1. Darmstadt University of Technology, Applied Plant Science, Schnittspahnstr. 10, D-64287 Darmstadt, Germany
Dodder or Cuscutaceae are holoparasitic plants subsisting on other di- or monocotyledonous plant hosts. The infection process is initiated by adherence of Cuscuta prehaustoria to the host surface, followed by penetration attempts of hyphae. For a better understanding of these processes, some of the genes expressed in host tissue or in the parasite were isolated and the products characterized. For example, contact of Cuscuta reflexa prehaustoria to tomato induced expression of a plasma membrane bound cell wall localized Arabinogalactan protein (attAGP) in the host, right at the site of dodder attack. Using RNAi-technique and targeted virus induced gene silencing, a correlation of attAGP expression level and the parasiteÕs attachment force to host tomatoes was observed. If the expression level of attAGP was reduced, C. reflexa attachment capability was also significantly reduced. C. reflexa infection induced a signal in the host leading to expression of tomato attAGP, which promotes the parasiteÕs adherence. On the other hand, Cuscuta expresses a cysteine protease, which could be inhibited by an intrinsic repressor. Circumvention of cysteine protease activity during an active parasitic infestation by spraying an inhibitor solution on the plants, leads to reduced growth or death of Cuscuta and completely heals the former host plant. Since the inhibitor is a polypeptide, it is suggested to use it as a biodegradable, non toxic, Cuscuta specific pesticide.
Kanampiu, F (1)
Striga Weed Management Options under Smallholder Agriculture in Africa
1. International Maize and Wheat Improvement Center (CIMMYT), United Nations Avenue - Gigiri, P.O. Box 1041-00621, Nairobi, Kenya Email: f.kanampiu[at]cgiar.org
Agriculture is the main source of livelihood for most households in Africa. Damage caused to three most important crops, maize, sorghum and pearl millet by Striga spp. in Africa is devastating to resource-challenged farmers whose main source of livelihood can be threatened by complete crop loss to this root-parasitic weed. A range of effective component technology control practices focusing on factors such as hoe weeding and hand pulling; use of inorganic fertilizer and manure; crop rotations, fallowing, and early planting; use of Striga tolerant varieties; soil fertility management and herbicides have shown value in reducing losses - but these have been poorly adopted and have thus failed to slow the spread of Striga . New technologies to deal with the high levels of Striga in African soils must meet four criteria to be widely adopted by farmers: (1) have the ability to control Striga early in its growing cycle in order to reduce yield loss; (2) deplete the Striga seed bank in the soil; (3) be cost effective; and (4) be compatible with existing cropping systems and technologies. The most promising new Striga control practice in maize is coating seeds with resistance to ALS-inhibiting herbicides with herbicides such as imazapyr prior to planting. Extensive on-farm testing in several African countries has demonstrated the cost effectiveness of this technology. It is highly effective in reducing Striga incidence two-fold - in terms of reduced seed bank in the soil and decreased infection in maize. Integration with other control options and deployment of this technology offers medium-term solution for an urgent Striga problem in Africa until breeders identify sources of resistance for the long-term.
Kusumoto, D (1), Yoneyama, K (1), Yoneyama, K (1), Takeuchi, Y (1)
Induction of Systemic Acquired Resistance in Root Parasitic Weeds
1. Weed Science Center, Utsunomiya University, 350 Mine-machi, Utsunomiya 321-8505, Japan. E=mail: kusumoto[at] cc.utsunomiya-u.ac.jp, fragrance0917[at]yahoo.co.jp, yoneyama[at] cc.utsunomiya-u.ac.jp, takeuchi[at]cc.utsunomiya-u.ac.jp
Induction of resistance was studied in red clover (Trifolium pratense) and rice (Oryza sativa) against root parasitic weeds by salicylic acid-mediated defenses. Experiments on the resistance induction in red clover against O. minor were carried out as follows. The seeds of red clover and O. minor were sown in pots packed with soil and incubated from the end of November in a greenhouse. Test chemicals were applied on the soil surface. Three months after incubation, the number of the tubercles was decreased by the treatment with BTH and tiadinil, inducers of SA-mediated defenses. Red clover seedlings were grown for 4 weeks in Petri dishes. The roots were treated with defense inducers for 3 hours. The seeds of O. minor treated with GR24 were sown on the roots of red clover. After a 5-week incubation, SA and BTH greatly reduced the number of the established parasites. The reduction was attributable to the development of haustoria before the radicle reached a host and the activation of defense responses in the host root including lignification of the endodermis. Experiment on resistance induction in rice against Aeginetia indica were carried out as follows. The seeds of rice (cv. Koshihikari) and Aeginetia indica were sown in pots packed with upland soil and tiadinil was applied to the soil surface. The pots were incubated in a greenhouse from the beginning of July. The shoots of A. indica emerged from the soil in late October in the non-treated pots. The number, height, and weight of A. indica shoots were decreased by the tiadinil treatment.
Lanini, WT (1), Miranda, M (2), and Aouali, S (1)
Dodder (Cuscuta pentagona) Control in Roundup Ready Alfalfa
1. Department of Plant Sciences, Mail Stop 4, University of California, One Shields Avenue, Davis, California 95616, USA. E-mail: wtlanini[at]ucdavis.edu, saouali[at]ucdavis.edu
2. Department of Horticulture, 146A Plant Science Bldg., Cornell University, Ithaca, New York, 14853, USA. E-mail: mrm67[at]cornell.edu
Dodder (Cuscuta pentagona and C. indecora) commonly infests alfalfa, reducing yield but also making it hard to dry after cutting. In greenhouse experiments, dodder (C. pentagona) was allowed to attach to Roundup Ready (RR) alfalfa, and treated with glyphosate at 0.84 or 1.68 kg ae/ha when dodder stems were 15 to 20 cm in length. Neither rate controlled dodder and dodder growth resumed within a week after treatment. Increasing glyphosate rate to 3.36 kg ae/ha or sequential treatments of 1.68 kg ae/ha made at two week intervals, resulted in 99% control. In a field study, dodder (C. pentagona) was allowed to attach to RR alfalfa. Glyphosate (0.84 or 1.68 kg ae/ha) or imazethapyr (0.10 kg ai/ha) treatments were made when the attached dodder stems reached 10 to 20 cm in length, with subsequent treatments applied two weeks later. Dodder control with glyphosate treatments was greater than 90% regardless of rate, while imazethapyr treatments provided less than 50% control. Imazethapyr treatment stunted the dodder, but dodder growth resumed within a few weeks. Following alfalfa harvest, dodder was observed to be completely controlled on all glyphosate plots except those that received a single application of the low rate (0.84 kg ae/ha). Although glyphosate effectively controlled dodder in the field study, further field testing is being conducted to verify this result, since dodder easily survived glyphosate treatment in greenhouse studies.
Lanini, WT (1), Miranda, M (2), and Aouali, S (1)
Riches, CR (1), and Mbwaga, AM (2)
Green manure: A Striga Management Technology Whose Time Has Come?
1. Natural Resources Institute, University of Greenwich, Chatham Maritime, Kent, ME4 4TB, UK. Email: Charlie[at]riches27.freeserve.co.uk
2. Uyole Agricultural Research Institute, Mbeya, Tanzania. Email: ambwaga[at]yahoo.co.uk
Soil fertility depletion contributes to low per capita food production and poverty in sub-Saharan Africa. An associated problem, often indicative soil fertility decline is increasing infestation of cereals by Striga asiatica. Farmer participatory research in Kyela District and Matambo Division of the Ulugulu Mountains in Tanzania has since 2000 identified low-cost approaches to increase agricultural productivity on Striga asiatica infested soils. Farmer groups in four villages in Kyela tested legume-cereal rotations and achieved average upland rice yield increases in 2003 and 2004 of 1114 (108%) and 827 kg ha-1 (72%) respectively when planting after growing the green manure Crotalaria ochroleuca the previous year and an additional 119 kg ha-1 (18%) when planting rice in 2004 after pigeon pea. Knowledge of the use of legume-rice rotations was disseminated to a further five communities and farmer-managed rice crops monitored in 2005 showed mean yield gains of 791 (74%) and 487 kg ha-1 (46%) when planted after Crotalaria or pigeon pea compared to continuous rice. Across 16 sites in Matombo in 2005 mean maize yield was increased by 180 and 153% following Crotalaria and pigeon pea respectively. Green manures are not new and there is a history of limited adoption of soil fertility technologies in sub-Saharan Africa. Understanding how farmers see soil fertility challenges, involving them in the selection of "best bets" and identifying the knowledge that farmers need to adopt new methods successfully has been central to laying the foundations for up-scaling adoption of green manure on Striga infested land.
Liu, Y (1), Liang, L (2) and Lynn DG (1)
Gene Regulation during Haustorial Development and Shoot Initiation in Striga asiatica
1. Center for Fundamental and Applied Molecular Evolution, Departments of Chemistry and Biology, 1515 Dickey Dr. NE, Emory University, Atlanta, GA 30322, USA.
E-mail: yliu4[at]emory.edu, dlynn2[at]emory.edu
2. University of Maryland Biotechnology Institute Center of Marine Biotechnology Suite 236, Columbus Center, 701 East Pratt Street, Baltimore, MD 21202, USA. E-mail: liangl[at]comb.umbi.umd.edu
In the parasitic angiosperms the vascular connection with the host occurs via formation of a specialized organ known as the haustorium. In Striga asiatica, a parasite of grasses, haustorial organogenesis is regulated by small molecules released from the host. Methods have now been developed for subtraction library screening of these obligate parasites. We now report the successful identification of two lignin biosynthetic genes -- chorismate mutase (StCM1) and cinnamyl alcohol dehydrogenase (StCAD1). The first StCM1 is the initial step in phenylalanine, tyrosine, and ultimately lignin biosynthesis, while the later StCAD1 is the last step in the formation of lignin monomers. The expression levels of both genes increases early in haustorial induction and remains elevated throughout organogenesis. The promoters of these two genes resulted in GUS expression specifically in the vascular tissue of Arabidopsis thaliana. Over-expression of StCM1 resulted in significant morphological changes, with the most remarkable change being a 50% increase in the number of stem xylem bundles. We discuss the possible reasons for this significant alteration of the Arabidopsis thaliana development program in the context of haustorial development. Using the same approach, we induced shoot initiation of Striga Asiatica by trans-zeatin, and constructed differential cDNA library to characterize the transcript profile that regulates shoot initiation.
Lozano-Baena, MD (1), Lindsey, K (2), Moreno MT (3), Rubiales, D (1), and
Pérez-de-Luque, A (3)
Laser Capture Microdissection (LCM): New Technologies Apply to Study of the Parasitic Plant Interactions
1. CSIC, Instituto de Agricultura Sostenible, 14080 C—rdoba, Apdo. 4084, Spain. Lozano-Baena: b72lobam[at]uco.es, Rubiales: ge2ruozd[at]uco.es.
2. School of Biological and Biomedical Sciences, University of Durham, South Road, Durham DH1 3LE, UK. Lindsey: keith.lindsey[at]durham.ac.uk.
3. IFAPA-CICE (Junta de Andaluc’a), Centro "Alameda del Obispo", çrea de Mejora y Biotecnolog’a, Apdo. 3092, 14080 C—rdoba, Spain. Pérez-de-Luque: bb2pelua[at]uco.es, Moreno: mariat.moreno.yanguela[at]juntadeandalucia.es.
Using Laser Capture Microdissection (LCM) technique, individual cells can be isolated from tissue sections for the profiling of gene expression. For these reason, we have chosen this method for RNA extraction of cells from tissues of M. truncatula infected with O. ramosa, an important parasitic plant pest of legumes crops. We selected M. truncatula as a model plant due to its similarities with other legumes which have complex genomes to analyze. Then we could analyze the infection process and the defense mechanisms against the attack of this pathogen. Basically, the slide with tissue of interest is placed under an inverted microscope and the image is transferred to a computer screen. A film-coated cap is placed onto the tissue. We select cells of interest and an infrared laser is pulsed at the selected region and heat generated determines the melting of the thermoplastic film from the cap with the tissue in correspondence to the demarcated region. Finally, the target region is selectively pulled away from the surrounding tissues when the cap is removed and samples are collected in a tube, now ready for molecular analysis. Other authors have analyzed this interaction using the whole tissues with the consequence being dilution of their RNA of interest in the total plant RNA. However, with this technique we attempted to analyze the transcriptome of target cells involved in the pathogenic process because we selected only the RNA of cell responding in this interaction.
Lozano-Baena, MD (1), Moreno, MT (2), Rubiales, D (1), and Pérez-de-Luque A (2)
Analyse of Medicago truncatula Resistance Against Orobanche crenata Using Citochemical Techniques
1. CSIC, Instituto de Agricultura Sostenible, 14080 C—rdoba, Apdo. 4084, Spain. Lozano-Baena: b72lobam[at]uco.es, Rubiales: ge2ruozd[at]uco.es.
2. IFAPA-CICE (Junta de Andaluc’a), Centro "Alameda del Obispo", çrea de Mejora y Biotecnolog’a, Apdo. 3092, 14080 C—rdoba, Spain. Pérez-de-Luque: bb2pelua[at]uco.es, Moreno: mariat.moreno.yanguela[at]juntadeandalucia.es.
Medicago truncatula has emerged as an important model plant species for structural and functional genomics. The close phylogenic relationship of M. truncatula with crop legumes (like faba bean, pea, vetches and lentil) increases its value as a resource for understanding resistance against Orobanche spp. Orobanche crenata is a root parasitic weed that represents a major constraint for grain legume production in Mediterranean and West Asian countries. Different cytological and histochemical methods (like stains, light and fluorescence microscopy, confocal studies, etc.) were used to study the mechanisms of resistance against O. crenata. For this study we have chosen two accessions of M. truncatula, showing early and late acting resistance. In the early resistance accession (Mt196) we found that the parasite died before a tubercle had formed. In the late resistance accession (Mt53) the parasite became attached without apparent problems to the host roots but most of the established tubercles turned dark and died before emergence.
Lopez-Raez, JA (1), Charnikhova, T (1,2), Gomez-Roldan, V (3), Matusova, R (1,2), de Vos, R (1), Schipper, B (1), Verstappen, F (1,2), Bino, R (1,2), Becard, G (3), and Bouwmeester, HJ (1,2)
The Biosynthesis of the Tomato Germination Stimulants is Promoted by Phosphate Starvation
1. Plant Research International, P.O Box 16, 6700 AA Wageningen, The Netherlands
2. Laboratory for Plant Physiology, Wageningen University, Arboretumlaan 4, 6703 BD Wageningen, The Netherlands
3. Laboratory for Cell Surfaces and Signalling in Plants, UMR 5546 Toulouse 3 University-CNRS, Catanet-Tolosan, France
Plants produce a large variety of secondary metabolites to defend themselves against harmful organisms and to attract others that are beneficial. One class of these important signaling compounds are the strigolactones which are secreted by plant roots in extremely low concentrations1. Strigolactones constitute a group of secondary metabolites produced by plants to attract symbiotic arbuscular mycorrhizal (AM) fungi under nutrient deficient conditions, inducing hyphal branching2. However, at the same time they are used by the root parasitic broomrapes (Orobanche spp) and whitchweeds (Striga spp) to germinate and complete their life cycle3,4. Tomato (Solanum lycopersicum L.) is an important fruit crop in southern Europe, the Americas, the Middle East, and India, with increasing production in China, Japan, and Southeast Asia and their production is highly susceptible to infestation by Orobanche ramosa and Orobanche aegyptiaca that cause severe yield losses up to 75%5. We focus on the biosynthetic origin of the strigolactone germination stimulants for O. ramosa and hyphal branching factor for Gigaspora rosea by tomato cv. MoneyMaker plants. For this purpose both the inhibitor of carotenoids fluridone and tomato mutants were used and analyzed for their strigolactone production, and the pivotal role of these metabolites under nutrient deficient conditions will be discussed. In addition, we will show the progress of our research at the molecular level in the isolation and characterization of genes coding enzymes involved in the biosynthesis of the tomato strigolactones.
Bouwmeester, H.J., et al. (2003) Current
Opinion in Plant Biology 6, 358-364
2. Akiyama, K., et al. (2005) Nature 435, 824-827
3. Akiyama, K., and Hayashi, H. (2006) Annals of Botany 97, 925-931
4. Bouwmeester, H.J., et al. (2007) Trends in Plant Science In press
5. Delavault, P., and Thalouarn, P. (2002). Gene 297, 85-92.
Matusova, R (1,2), and Bouwmeester, HJ (1,2)
The Strigolactone Germination Stimulants of the Plant-Parasitic Striga and Orobanche spp are Derived from the Carotenoid Pathway
1. Plant Research International, P.O. Box 16, 6700 AA Wageningen, The Netherlands.
2. Laboratory for Plant Physiology, Wageningen University, Arboretumlaan 4, 6703 BD Wageningen, The Netherlands E-mail: Matusova radoslava.matusova[at]wur.nl, Bouwmeester harro.bouwmeester[at]wur.nl
The seeds of the root-parasitic Striga and Orobanche spp are only able to germinate after induction by a chemical compound(s) exuded from the roots of their host. For both Orobanche and Striga spp. several germination stimulants were identified from host and non-host plants. In most cases, the compounds were shown to be isoprenoid and belong to one chemical class, collectively called the strigolactones. Strigolactones have been detected in many plant species showing that they are wide-spread in the plant kingdom. Because the germination stimulants are produced/exuded in extremely low concentrations, an analytical approach to discover the biosynthetic origin of the germination stimulants is difficult. Therefore we used the high sensitivity of parasitic plant seeds to the germination stimulants and used a germination bioassay-guided approach to unravel the biosynthetic pathway. To assess the involvement of the isoprenoid biosynthetic pathways we investigated the induction of Striga hermonthica seed germination by root exudates of maize seedlings treated with inhibitors and of a series of maize mutants. We also used these inhibitors on cowpea (Vigna unguiculata) and sorghum (Sorghum bicolor) and assessed the effects on the root exudate-induced germination of S. hermonthica and Orobanche crenata. Our results demonstrate that the germination stimulants of S. hermonthica present in the root exudates of maize, cowpea and sorghum are derived from the carotenoid biosynthetic pathway. Based on these results, we have postulated a biogenetic scheme for the strigolactone germination stimulants.
Miegel, D (1), Hayton, D (1), and Matthews, JM (1)
Seedbank and Seedbank Management of Orobanche ramosa in South Australia.
1. School of Agriculture, Food and Wine; University of Adelaide, PMB 1 Glen Osmond, South Australia 5064, Australia.
The discovery of Orobanche ramose L. in 1992 in South Australia has lead to an intensive research and eradication effort. Seedbank longevity studies were initiated in 2002 and will be discussed, twice yearly exhumations are done but no significant reduction has been observed. Seed eradication with a soil drench "Bio Seed-Eradicator" containing novel, environmentally safe active ingredients has proved successful with up to 98% seed death. Trial results will be presented and discussed. Many herbicides and adjuvants have been tested with complete suppression of emergence from some products. Mainly conventional crop species have been involved but herbicide tolerant canola and herbicide tolerant Medicago have great potential due to a larger number of potent herbicides. Management leading to eradication will be discussed.
Murdoch, AJ (1), and Kebreab (2)
Predictive Empirical Modeling of Parasitic Weed Life Cycle
1. Department of Agriculture, The University of Reading, P.O. Box 237, Earley Gate, Reading, RG6 6AR, UK. Email: a.j.murdoch[at]reading .ac.uk
2. Centre for Nutrition Modelling, Department of Animal and Poultry Science, University of Guelph, Guelph, Ontario N1G 2W1, Canada.
Dormancy in Orobanche
removed as a two-stage process. First, after
shedding from the mother plant, populations of dry Orobanche seeds
after-ripen (lose primary
dormancy). Increasing the temperature results in a faster
of the seed population. The second stage - conditioning - occurs at
potentials close to full imbibition. The rate of conditioning in the
population also increases with increase of temperature. Secondary or
tertiary processes may interfere with dormancy loss. For example,
the conditioning period beyond about 21 days decreases the subsequent
germination response due to a) induction of secondary dormancy and b)
temperatures over about 25˚C, loss of viability in the case
of Orobanche. Germination
of conditioned seeds
depends on chemical stimulation from host's roots,
temperature and water
stress. The thermal time for germination is strongly affected by water
potential. Non-linear probability models account for these processes
provide predictive empirical models to describe the germination
behavior of the
seed population. This paper discusses whether additive or
are more appropriate for conditioning responses and explores the
of these results for parasitism of crop plants.
Nickrent, DL (1), and Vidal-Russell, R (1)
The Evolutionary Origins of Aerial Parasitism in Santalales
1. Department of Plant Biology, Southern Illinois University, Carbondale, IL 62901-6509, USA.
E-mail: nickrent[at]plant.siu.edu, romina[at]siu.edu.
Molecular phylogenetic work in the sandalwood order (Santalales) has progressed to the point where multiple DNA sequences of nuclear and plastid genes are available for nearly all of the 146 genera. Moreover, phylogenetic methods have matured with the development of model-based methods such as maximum likelihood (ML) and Bayesian inference (BI) that more effectively deal with rate heterogeneity - an issue with some parasitic plant lineages. Past work showed that aerial parasitism evolved five times independently in Santalales, but the relative timing of these diversifications was not addressed. DNA sequences from five genes were obtained from 39 taxa representing all families in Santalales. These data were analyzed using ML and BI and time estimates were performed with a Bayesian relaxed molecular clock and penalized likelihood methods. The trees were calibrated using published fossil data from Santalales and an outgroup. These analyses showed that aerial parasitism first arose in Misodendraceae ca. 89 Mya and subsequently in Viscaceae (81 Mya), "Eremolepidaceae" (62 Mya), tribe Amphorogyneae in Santalaceae (53 Mya), and Loranthaceae (30 Mya). The rapid adaptive radiation and speciation in Loranthaceae coincides with the appearance of savanna biomes during the Oligocene. Reconstructing the character "parasite mode" on the tree suggests that all lineages except Misodendraceae evolved from ancestors that were polymorphic for either root or stem parasitism. Features found in more derived aerial parasites, such as the squamate habit, unisexual flowers, and loss of chlorophyll, have evolved independently and thus represent convergences and parallelisms.
Ogbebor, NO (1), Omorusi, VI (1) and Evueh, GA (1)
Evaluation of Mistletoe Incidence on Nine Rubber Clones and its Effects on Latex Yield in Nigeria
1. Plant Protection Division/Microbiology Division, Rubber Research Institute of Nigeria, P.M.B. 1049, Iyanomo Benin City. E-mail: Ogbeb06[at]yahoo.com. Telephone: +08055338839
Incidence of mistletoe on nine rubber clones consisting of three exotic (PR107, RRIM 707 and GT1) and six developed clones in Rubber Research Institute of Nigeria (NIG 800, 801, 802, 803, 804 and 805) were evaluated. The effect of mistletoe on rubber production was also observed. The results showed that GT1 clone were more susceptible to mistletoe attack with disease index of 19.22. This was followed by Nig 801 clone which had a disease index of 12.23. RRIM 707 recorded the lowest disease index of 2.37. The experiment further demonstrated that trees with severe infestation gave the highest rubber production in the weights fresh cup - lumps and dry weights of cup - lumps.
Okazawa, A (1), Wada, Y (1), Fukusaki, E (1), Yoneyama, K (2), Takeuchi, Y (2),
Trehalose Promotes Seed Germination of a Holoparasitic Plant, Orobanche minor Sm.
and Kobayashi, A (1)
1. Department of Biotechnology, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan E-mail: okazawa[at]bio.eng.osaka-u.ac.jp, fukusaki[at]bio.eng.osaka-u.ac.jp, kobayashi[at]bio.eng.osaka-u.ac.jp
2. Weed Science Center, Utsunomiya University, 350 Mine-Machi Utsunomiya 321-8505, Japan E-mail: yoneyama[at]cc.utsunomiya-u.ac.jp, takeuchi[at]cc.utsunomiya-u.ac.jp
Parasitic plants greatly damage crops mainly in the semiarid Mediterranean regions. The establishment of technology to prevent their reproduction is eagerly required. It is well known that germination stimulants are required for the germination of the parasites. The seeds have to imbibe water at suitable temperature in the dark for several days to have the potential to accept the germination stimulants. This process is called conditioning. In this paper, metabolic profile of hydrophilic primary metabolites in seeds of Orobanche minor Sm. during the conditioning period was analyzed by GC/MS. As a result, 25 metabolites, such as organic acids, amino acids and sugars, were identified. Among them, the amount of trehalose significantly increased during conditioning. So we investigated the effect of exogenous trehalose on the germination. When 0.1 to 1% of trehalose was supplied during conditioning, the germination rates were increased 15% to 20%. This effect was also observed with germination inhibitors such as abscisic acid and glucose. Trehalose is hydrolyzed to two glucose molecules by trehalase in plants. Validamycine A, which is an inhibitor of trehalase, was shown to increase the endogenous trehalose and consequently the germination rates of O. minor, when it was supplied during conditioning period. From these results, we concluded that trehalose is synthesized during conditioning and has positive effect on the seed germination of O. minor. This information might be helpful to establishment of an efficient system of suicidal germination to prevent parasitic weeds.
Pacureanu-Joita, M (1), Raranciuc, S (1), Procopovic, E (2), and Sava, E (1)
AO - 548, a Sunflower Inbred Line, Carrying Two Genes for Resistance Against a New Highly Virulent Romanian Population of Orobanche cumana.
1. Agricultural Research and Development Institute Fundulea, N. Titulescu, 1, 915200, Fundulea, Romania. E-mail: pacurean[at]ricic.ro, mariapacureanu2[at]yahoo.com
2. Agricultural Research and Development Station, Valul lui Traian, Constanta, Romania
A new highly population of the parasite Orobanche cumana has attacked sunflower crop in Romania, in 2005 year. In the sunflower germplasm collection of Fundulea institute has been identified a restorer line, AO - 548, full resistant to this new broomrape population.
Since this line could be used directly as a parent to produce commercial F1 hybrid seed, as well as a source of resistance to broomrape in sunflower breeding programm, it was decided to study
the inheritance of resistance in this line, to the new population of Orobanche cumana. Using the cytoplasmic male sterile inbred line AD - 66, known to be very susceptible to this population of the parasite, as a female parent, progenies of a cross with AO - 548 (including F1, F2, and BC1 to both parents), as well as the parental lines, were analyzed for their reaction to this broomrape population. The goodness of fit of the observed vs expected segregation ratio (15:1and 3:1) indicated that the inheritance of resistance to broomrape in the line AO - 548 is confered by two independent dominant genes.
Palmer, AG(1), Liang, L (1), Keyes, J (1), and Lynn, DG (1)
ROS production and Semagenesis in Pathogenesis
1. Emory University Department of Chemistry, 1515 Dickey Dr., Atlanta, Ga. 30322
The potential of reactive oxygen species (ROS) such as superoxide (O2●-) and hydrogen peroxide (H2O2) to induce oxidative stress (damage) in biological macromolecules is well established. While ROS production is well-known as a byproduct of oxidative metabolism and co-opted by eukaryotes as a common component of the response to wounding and/or infection, these potent oxidants have recently been implicated as signaling molecules in a number of critical developmental events. In the parasitic plant Striga asiatica, ROS regulates host detection and organogenesis of the haustorium, a specialized organ for host attachment. S. asiatica seedlings produce H2O2 which serves as the co-substrate with host cell wall phenols and apoplastic peroxidases to release haustorial inducing p-benzoquinones in a process we have named semagenesis. Employing a variety of H2O2-responsive stains in conjunction with confocal, florescence, and transmission electron microscopys, we have localized the site of H2O2 production and characterize its regulation. These results support a model in which ROS generated by the parasite is a critical component of the signaling process and required for haustorial organogenesis. We therefore suggest that ROS may function in a semagenic role in the oxidation of cellular components in other organisms, perhaps in conjunction with other small molecules or enzymes, generating secondary signaling products.
Palmer, AG (1), Liang, L (1), O'Malley, R (1), and Lynn, DG (1)
Calcium Mediated Transduction of Haustorial Inducing signals in Striga asiatica
1. Emory University Department of Chemistry, 1515 Dickey Dr. Atlanta, Ga. 30322
The sessile nature of plants has dictated a life plan in which development is tightly coupled to external signals in order to maximize survival. Such signals are then integrated through internal signaling pathways (i.e. Ca2+ and/or hormones) resulting in developmental changes. Deciphering the mechanisms of signal integration and subsequent organogenesis could have substantial agricultural benefits and may also shed some light on the developmental plasticity common to plants but largely absent in many other eukaryotes. In the parasitic angiosperm Striga asiatica, haustorium formation is initiated by the presence of host derived p-benzoquinones and is characterized by a halt in vegetative growth, swelling of the root tip, and the formation of haustorial root hairs. As both the initiating signal and the physical characteristics of the haustorium have been clearly defined for this parasite, S. asiatica represents an opportune system in which to explore the perception of host derived signals, or xenognosins, as well as pathogen development. From root hairs to pollen tubes directed growth, events are often mediated by elevated cytoplasmic calcium concentrations. Hypothesizing that both swelling and haustorial hair formation might be similarly regulated events we employed a variety of calcium chelators, channel inhibitors, and fluorescent probes to evaluate the importance of calcium in organogenesis. Our findings suggest that the perception of haustorial inducing xenognosin results in the rapid influx of calcium from an extracellular source, presumably the cell wall, which is crucial to further genetic and biochemical regulation. Furthermore, this work establishes rapid cytoplamic calcium elevation, over a 15 minute period, upon introduction of the signal as the earliest component in the process of haustorial organogenesis observed to date.
Palmer, J (1)
Horizontal Gene Transfer Gone Wild in Parasitic and Other Flowering Plants.
1. Department of Biology, Indiana University, Bloomington, IN 47405. E-mail: jpalmer[at]indiana.edu
I will review the published evidence and present unpublished data showing that there has been considerable transfer of mitochondrial genes between parasitic plants and their host plants during angiosperm evolution. This transfer has occurred in both directions, from host to parasite and vice-versa. A model will be presented explaining why transfers can involve very large regions of the mitochondrial genome, why mitochondrial gene transfer is relatively frequent, and why chloroplast gene transfer is never seen.
Pérez-de-Luque, Alejandro (1)
Mechanisms of Resistance to Parasitic Plants: from Field Screenings to Laboratory Microscopic Studies
1. IFAPA-CICE (Junta de Andaluc’a), Centro "Alameda del Obispo", çrea de Mejora y Biotecnolog’a, Apdo. 3092, 14080 C—rdoba, Spain. E-mail: bb2pelua[at]uco.es
From about 4,000 species of parasitic angiosperms, only very few of them are weedy and parasitize cultivated plants. Among the main genera are Orobanche, Striga, and Cuscuta. The available control methods have not proven to be as effective, economical and applicable as desired. The only way to cope with the weedy root parasites is through an integrated approach, employing a variety of measures in a concerted manner. Genetic resistance remains as one of the most desirable components in an integrated control strategy. Because resistance is a multi-component event, understanding the physiological and genetic basis of such resistance at the different stages of the infection process will improve its utility as a control measure and assist in being attempts to integrate diverse mechanisms of resistance from different sources (including wild relatives) into a single cultivar (i.e., pyramiding multiple mechanisms of resistance). However, the basic mechanisms governing resistance to parasitic plants remain undiscovered. Furthermore, unlike the large core knowledge base available in other pathosystems, the molecular basis of the parasitic plant-resistant host interactions is still at a very preliminary stage. In this way, traditional histological methods are valuable tools in order to preliminarily unveil the defensive mechanisms leading to resistance. Recently, the combination of histological methods with molecular techniques (molecular histology) has been shown to be a powerful tool to increase our understanding and knowledge about the infection and resistance processes. We will try to give an overview about what is known on the mechanisms of resistance against root parasitic plants, mainly centred in broomrapes (Orobanche spp.).
Plakhine, D (1), Tadmor, Y (1), Levin, I (2) and Joel, DM (1)
Non-Stimulated Spontaneous Germination of Orobanche is Genetically Controlled
1. Newe-Ya'ar Research Center, ARO, PO. Box 1021, Ramat-Yishay 30095, Israel.
E-mail: dinap[at]agri.gov.il; tadmori[at]agri.gov.il; dmjoel[at]volcani.agri.gov.il
2. The Volcani Center, ARO, PO. Box 6, Bet-Dagan 50250, Israel.
A fundamental step in the evolution of the angiospermous root holoparasites is their ability to germinate only in response to stimulants that are released by host roots. Germination away from a host leads to seeding death. We assumed that the trait requiring stimulant receptivity evolved by the development of genes that inhibit germination, and switch off inhibition upon chemical stimulation. By analyzing inter-specific hybrid populations of Orobanche cernua and Orobanche cumana, segregating for spontaneous germination that occurs without chemical stimulation, we identified genes that are involved in germination control. The segregation results correspond to the expectation that two epistatic genes are responsible for this germination control. Our model suggests that one root parasite dormancy gene (Rpdg1) is a regulator of non-stimulated germination, with a dominant negative control on the expression of Rpdg2 gene. We hypothesize that Rpdg1 is involved in seed dormancy, and Rpdg2 in the reception or transduction of the germination stimulus. For spontaneous germination a seed should express the recessive alleles of Rpdg1 and the dominant allele of Rpdg2. Our results agree with the 3:13 (spontaneous vs non-spontaneous germination) ratio in the first segregating generation, which matches to our assumption that one parent species possess the two dominant genes, and the other has the two recessive genes. These results indicate that spontaneous germination of Orobanche is genetically controlled. Such genetic control ensures a low incidence of this lethal trait among natural parasite populations, and increases the rate of its successful germination in the vicinity of host roots.
Roney, JK (1), Khatibi, PA (1), Stromberg, VK (1), and Westwood, JH (1)
Trafficking of Host mRNAs into Dodder: A New Frontier in Host-Parasite Communication
1. Department of Plant Pathology, Physiology and Weed Science, Virginia Tech, Blacksburg, VA 24061-0392 USA. E-mail: westwood[at]vt.edu
Dodders (Cuscuta spp.) have especially open connections to the host phloem and have been shown to obtain simple sugars, phloem-specific dyes, proteins, and viruses from their hosts. We have now shown that phloem-mobile mRNAs can also move from pumpkin (Cucurbita maxima Duch.) and tomato (Lycopersicon esculentum Mill.) hosts into attached lespedeza dodder (Cuscuta pentagona Engelm.). Tomato microarrays were used to probe RNA from dodder growing on tomato to reveal 474 putatively mobile transcripts. From this pool, over 50% of those tested have shown evidence of mobility based on sequence comparisons of reverse transcriptase PCR products generated from RNA of tomato, dodder grown on tomato, and dodder grown on other host species. To date, 21 tomato transcripts have been identified from dodder, including GAI, (Gibberellic acid insensitive), which has been previously shown to be translocated in the phloem of tomato. Host-to-parasite movement of mRNA indicates a potentially new mechanism of interspecies communication, and raises many questions. For example, are the mobile host mRNAs used by the parasite to gain information about host physiological status? Does dodder distinguish host mobile mRNAs from its own, leading to selective accumulation or degradation of host mRNAs? Finally, the ability of dodder to form connections to taxonomically distant host plants simplifies identification of host mRNAs, so it is possible that dodder may be a useful tool for studying non-cell-autonomous RNAs in other plants.
Saadoun, I (1), Hameed, KM (2), Ababneh, Q (1), Bataineh, S (1) and Foy, CL (3)
Biological Control of Orobanche cernua Seed Germination Utilizing an Indigenous Actinomycete Isolate in Jordan
1. Department of Applied Biological Sciences, Faculty of Science, Jordan University of Science and Technology, Irbid-22110, Jordan. Fax: 962-2-7201071 E-mail: isaadoun[at]just.edu.jo, qoia_16[at]yahoo.com, sereen_b[at]yahoo.com
2. Department of Plant Production, Faculty of Agriculture Jordan University of Science and Technology, Irbid-22110, Jordan. Fax: 962-2-7201071, Emerate Prof. VPI&SU Blacksburg, VA, USA, E-mail: hameed[at]just.edu.jo
3. Department of Plant Pathology, Physiology and Weed Science, Virginia Polytechnic Institute and State University, Blacksburg, VA, USA, E-mail: cfoy[at]vt.edu
An indigenous Streptomyces isolate, R9, was recognized to have phytotoxic activity against seed germination of weeds. It was also evaluated for its potential activity against Orobanche cernua seed germination under laboratory conditions. Cell-free culture filtrate (1 liter) of R9 (grown on glucose peptone molasses (GPM) in shaken broth culture for 7 days at 28˚C) was lyophilized. Sterile distilled water and GPM broth were used as controls. Preconditioned O. cernua seeds were uniformly spread on the surface of water agar plates and irrigated with 1 ml of either lentil Lens esculenta root exudates or GR-24 (0.2 μg/l) as germination stimulus several hours before treatment. R9 extracts (250 µl) were transferred into wells (10 mm in diameter) cut in the center of each plate. Plates were incubated in a humid incubator at 25˚C for 3 days, then percent seed germination was calculated around wells using a dissecting microscope at 45 X. Results showed 0% O. cernua seed germination for the R9 culture filtrates in contrast to 31.3% to 50% and 2.3% to 8% seed germination in the water and GMP controls, respectively, in duplicate experiments. Hence, R9 may be considered as a potential source for bio-herbicides to control Orobanche.
Sandler, HA (1)
Integrating Germination Patterns, Chemical, and Nonchemical Options to Manage Swamp Dodder in Massachusetts Cranberry Production
1. UMass Cranberry Station, 1 State Bog Road, PO Box 569, East Wareham, MA 02538, USA. hsandler[at]umext.umass.edu
Current recommendations in Massachusetts cranberry production for the control of dodder, Cuscuta gronovii, include the use of horticultural practices (e.g., application of uniform sand layers) along with the application of preemergence herbicides. Multiple control strategies are needed to keep dodder from significantly reducing yields on an annual basis. A 2-year project was evaluated the efficacy of short-term floods (24 to 48 hr) for the control of dodder. In addition, using simulated bogs constructed in plastic containers, the germination patterns of MA dodder seed has been monitored for 9 years. Both studies should provide important information that will help growers improve the timing of management strategies. Grower trials and controlled research studies with flooding have documented variable effects that may be related to timing the flood to coincide with a certain period of seedling emergence. Dodder seeds apparently have a definitive peak of germination in the initial year after seeding. Peaks can still be seen in subsequent years, but they are much lower. Over the course of this 9-year study, the peak germination period occurred later each year. The delay of peak germination from populations in the seedbank causes overlapping generations to exist in a single farm field. This may contribute to the difficulties growers have in managing dodder. Since most herbicides targeting dodder can only be efficacious for a specific window of time, a portion of the population may always escape preemergence control and provide enough viable seedlings to cause substantial infestations in the vine canopy.
Schneeweiss, GM (1), Park, JM (2), Manen, JF (3), and Colwell, AE (4)
Phylogeny and Evolution of Orobanche and Related Genera (Orobanchaceae)
1. Department of Biogeography, University of Vienna, Rennweg 14, A-1030 Vienna, Austria. Email: gerald.schneeweiss[at]univie.ac.at
2. Department of Systematic and Evolutionary Botany, University of Vienna, Rennweg 14, A-1030 Vienna, Austria
3. Conservatoire et Jardin Botaniques, Impératrice 1, CH-1292 Chambésy/Gen�ve, Switzerland
4. U.S. Geological Survey, Western Ecological Research Center, Yosemite Field Station, 5083 Foresta Road, El Portal, California 95318, USA
In recent years, molecular phylogenetic studies have greatly enhanced our understanding of the phylogenetic relationships of Orobanche and related genera. These data suggest splitting Orobanche into (at least) four segregates in agreement with previous suggestions based on morphological and karyological evidence. These genera show partly different evolutionary trajectories, e.g., incidence of polyploidy or diversity and evolution of retrotransposons. Irrespective of taxonomic consequences, the phylogenetic framework allows rigorous testing of character evolution, e.g., the evolution of genome size or the correlated evolution of host range and life span. Additionally, Orobanche and related genera may show features of general interest, such as the occurrence of horizontal gene transfer.
Scholes J. (1), and Press, M. (1)
The Molecular Basis of Susceptibility and Resistance to Striga: insights from Transcript Profiling
1. Department of Animal and Plant Sciences, University of Sheffield, Sheffield, S10 2TN, UK
Striga species are among the most devastating parasites of subsistence farming agriculture in sub Saharan Africa yet our knowledge of the mechanisms underlying host susceptibility and resistance lags behind that of fungal and bacterial pathogens. Understanding these processes at a molecular level is a critical step in the identification of genes that can be used for improving crop productivity via biotechnology based approaches, or via the development of molecular markers for use in marker assisted selection programmes. In a susceptible interaction, the Striga radical/haustorium attaches to the host root and the endophyte penetrates the epidermis, cortex and endodermis finally forming xylem continuity with the host. Once attached, both S. hermonthica and S. asiatica cause profound effects on the development and growth of the host plant. Recently we have examined changes in gene expression during a susceptible interaction between rice and S. hermonthica using Affymetrix oligonucleotide microarrays. Perhaps the most striking result was the extent of the down-regulation of gene expression that takes place as Striga develops on roots of the susceptible cultivar; of the 2588 genes that were differentially regulated, 553 were up regulated whereas over 2000 were down regulated. The down regulated genes included those purportedly involved in metabolism, cell cycle and DNA processing, transcription, protein synthesis and fate, cellular communication and signal transduction. Plants exhibit two different types of resistance; non host resistance where plants are resistance to all isolates of a particular pathogen species and host/race-specific resistance where they are resistant to some but not all isolates of a pathogen. In the latter, defense responses are triggered following the recognition by resistance gene (R-gene) products of specific pathogen or host derived elicitors. Whilst a large body of information is available concerning the molecular architecture of resistance to microbial pathogens very little is known about plant-plant resistance responses. In order to investigate the molecular basis of resistance to S. hermonthica, changes in gene expression were profiled in (1) the rice cultivar Nipponbare which exhibits host specific resistance and (2) Arabidopsis thaliana which is a non host to this parasite. In both cases over 1000 genes were significantly up or down regulated. The greatest number of genes was most strongly up regulated 24 hours post inoculation consistent with active host resistance responses. Functional analyses revealed that large numbers of genes involved in cell wall synthesis, defense signaling, regulation of transcription and protein synthesis, oxidative stress and primary and secondary metabolism were up-regulated but there were differences between the host and non host interaction. A key feature of the non host interaction was the up-regulation of many genes (EDS1, EDS5, PAD3, NPR1, NIMIN1, PR2) and WRKY transcription factors involved in the salicylic acid signaling pathway. Finally, susceptibility and resistance mechanisms will be considered in the context of physiological and metabolic interactions between host and parasite and a brief comparison drawn between plant-plant interactions and those involving interaction of plants with other taxa.
Shamoun, SF (1), Rietman, LM (2), Askew, SE (2), and van der Kamp, BJ (2).
Development of a Biological Control Strategy for Management of Hemlock Dwarf Mistletoe in Coastal British Columbia, Canada
1. Natural Resources Canada, Canadian Forest Service, Pacific Forestry Centre, 506 West Burnside Road, Victoria, BC V8Z 1M5 Canada
2. Department of Forest Sciences, Faculty of Forestry, University of British Columbia, Vancouver, BC V6T 1Z4 Canada
The purpose of this research is to assess the indigenous fungi Neonectria neomacrospora (pathosystem 1) and Colletotrichum gloeosporioides (pathosystem 2) as biological control agents for the conifer parasite hemlock dwarf mistletoe (HDM; Arceuthobium tsugense). Two separate field trials were conducted on Vancouver Island. Treatments for pathosystem 1 involved spraying Stabileze formulated conidia onto unwounded and wounded HDM swellings and cut HDM shoots. Treatments for pathosystem 2 involved spraying Stabileze formulated conidia onto unwounded HDM swellings and cut HDM shoots, and spraying Sucrose-gelatin formulated conidia onto unwounded HDM swellings. The objectives of both field trials were to: (1) determine the efficacy of treatments in establishing infection, and (2) measure the impact of infection on HDM shoot health and number. Results for pathosystem 1 suggest that applying inoculum to wounded HDM swellings had a greater impact on N. neomacrospora infection than applying inoculum to unwounded HDM swellings or cut HDM shoots. HDM swellings with confirmed N. neomacrospora infection (isolation of the fungus and (or) presence of sporodochia) had their numbers of healthy mistletoe shoots significantly reduced by 1.6 or about 36% when compared with HDM swellings with unconfirmed infection (P=0.014). Results for pathosystem 2 showed stabileze and sucrose-gelatin formulated conidia treatments reduced the current berry crop by 16-36%, respectively (P=0.05). While the results for shoots appeared promising, heavy background infection and/or secondary infection, especially on controls, limited the ability to detect clear treatment effects. The implications of these results in variable retention silviculture systems and future research will be discussed.
Stefanovic, S (1), and Costea, M (2)
Reticulate Evolution in the Parasitic Genus Cuscuta (Dodders; Convolvulaceae)
1. Department of Biology, University of Toronto, Mississauga, Ontario L5L 1C6, Canada
2. Department of Biology, Wilfrid Laurier University, Waterloo, Ontario N2L 3C5, Canada
The frequency and relative importance of hybridization in plants has been an area of intense debate. Although this evolutionary mechanism has received considerable attention from plant biologist, there are no well-supported cases of reticulate evolution involving holoparasitic plants to date. Recent molecular phylogenetic analyses revealed that the subgenus Grammica, the largest and most diverse group of the stem parasitic genus Cuscuta, consists of 15 major clades. We describe here five cases of strongly supported discordance between phylogenies derived from plastid and nuclear data and interpret them as results of five independent hybridization events. Three of these cases probably represent relatively recent reticulations because each of them involves more closely related species, always confined within the same major clade as their putative parental species, and are sympatric/parapartric in distribution with them. In contrast, the two remaining cases involve species whose potential progenitors are derived from different major groups of Grammica and are allopatric in their present distribution. This is consistent with more ancient hybridization events. Exemplary taxa illustrating these two cases (i.e., Cuscuta subsection Denticulatae and Cuscuta sandwichiana, respectively) are discussed in more detail.
Sugimoto, Y (1), Ueyama, T (1), and Yasuda, N (1)
In vitro Production of Strigolactones by Plant Root Cultures
1. Graduate School of Science and Technology, Kobe University, Rokkodai, Nada, Kobe 657-8501, Japan
Plant tissue culture, where aseptic conditions are maintained and cultural parameters are easily manipulated is a useful technique for investigating the biosynthetic pathways of target molecules. Preliminary screening of plant tissue cultures in our laboratory revealed that root cultures of Menispermum dauricum, Stephania cepharantha (Menispermaceae) and Lotus japonicus (Leguminosae) are copious producers of potent Striga hermonthica seed germination stimulants. EtOAc extracts of Menispermum and Stephania root culture filtrates induced considerable germination of S. hermonthica seeds, however, the hexane extract exhibited no activity. EtOAc and hexane extracts of L. japonicus root culture filtrate contained potent S. hermonthica germination stimulants. HPLC analysis of EtOAc extracts of Menispermum and Stephania root culture filtrates, each, showed one major fraction with germination-inducing activity, while that of L. japonicus root culture filtrate showed more than seven fractions with considerable activity. (+)-Strigol was isolated from EtOAc extracts of M. dauricum root culture filtrate. A major stimulant produced by Stephania cepharantha showed identical chromatographic behavior and molecular mass to authentic strigol. (+)-5-deoxystrigol was isolated from hexane extracts of L. japonicus roots extract and culture filtrate. The strigolactones were identified on basis of NMR, UV, MS and CD spectra and chromatographic behaviour on HPLC. Purification and identification of S. hermonthica germination stimulants from EtOAc extracts of L. japonicus roots and culture filtrate are currently under way. Authentic (+)-5-deoxystrigol was as active as GR24 in inducing germination of Striga hermonthica and O. crenata seeds. However, it was about 10- fold more active than GR24 in inducing O. minor seed germination.
Takagi, K (1), Okazawa, A (1), Wada, Y (1), Trakulnaleamsai, C(1), Fukusaki, E (1), Yoneyama, K (2), Takeuchi, Y (2), and Kobayashi, A (1)
Photoresponse Analysis of Phytochrome A in the Non-photosynthetic Parasitic Plant; Orobanche minor Sm.
1 Department of Biotechnology, Graduate school of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan. E-mail: okazawa[at]bio.eng.osaka-u.ac.jp, takagi_kazuteru[at]bio.eng.osaka-u.ac.jp
2 Weed Science Center, Utsunomiya University, 350 Mine-machi, Utsunomiya, 321-8505, Japan
Among environmental factors, light induces various morphological responses. Photoreceptors are involved in these responses. Among photoreceptors, phytochrome is the major red and far-red light photoreceptor. After light perception, phytochromes localize from the cytoplasm to the nucleus and control the expression of downstream genes. The entire network of light signaling has not yet been elucidated because of its complexity. Therefore, we studied phyA of non-photosynthetic parasitic plant, Orobanche minor. This plant cannot photosynthesize and acquires its energy from the host plant. It is thought that Orobanche minor has the light signaling system related to photosynthesis partially altered, but it retained the function necessary to regulate morphogenesis. The amino acid sequence of OmphyA was compared to that of AtphyA from Arabidopsis thaliana. The result revealed that OmphyA has 26 amino acid substitutions and 71% sequence identity. These substitutions are largely located around functional domains. Therefore, we compared the physiological responses of O. minor with photosynthetic plants to find functional differences. As a result, OmphyA has the same biological characteristics as its counterparets in green plants. For the photoresponses, OmphyA has the same role as the green plant in germination and accumulation of anthocyanin. OmphyA plays an opposite role in inhibition of the stem elongation. By the usage of A. thaliana, it was revealed that the expression level of genes involved in phyA signal network was different in OmphyA and AtphyA transfected protoplasts. These results suggest that OmphyA function is different from that of AtphyA, and these differences may attribute to amino acid substitutions of OmphyA.
Tennakoon, KU (1), Bolin, JF (2), and Musselman, LJ (2)
Structural and Functional Attributes of the Hypogeous Root Holoparasite Hydnora triceps Drege & Meyer (Hydnoraceae)
1. Department of Botany, University of Peradeniya, Peradeniya 20400, Sri Lanka. E-mail: kushant[at]pdn.ac.lk
2. Department of Biology, Old Dominion University, Norfolk, VA 23529, USA. E-mail: jbolin[at]odu.edu, lmusselm[at]odu.edu
Acholorophyllous root holoparasites with extremely reduced vegetative bodies, Hydnora spp. are the only known angiosperms lacking leaves and scales. Hydnora occur in the arid regions of Africa and the southern portion of the Arabian peninsula. Five species are currently recognized in this genus. The most remarkable species, H. triceps completes its entire lifecycle below ground. The reduced vegetative structure of H. triceps raises two important questions: (i) How does the vegetative body grow and attain its distinctive structural entity? and (ii) By what means does it make intimate connections with its host and fulfill water and nutrient requirements? The vegetative body consists of "pilot roots", poorly studied structures bearing haustoria and flowers. Our studies showed a "chimeral" apical structure and a protective layer of cells similar to a root cap at the growing tip. However, eustelic, endarch and collateral vascular bundles and the continuous pith indicate that pilot roots are stems. Increased girth is due to the fascicular cambium, periderm and strands of cells distributed in the main vegetative body similar to a primary thickening meristem. The haustorium and the reproductive structures of H. triceps initiate exogenously from the "root bumps" (outgrowths of the vegetative body). An endophytic primodium penetrated the host root with a stratified meristem giving rise to xylary and pholic hyphae, and transfer cells.
Tennakoon, KU (1)
Potential of Establishing Root Hemiparasitic Sandalwood (Santalum album L.) as a NTF Species in the Buffer Zones of Forests and Degraded Lands in Australasia: a Sri Lankan Experience
1. Department of Botany, University of Peradeniya, Peradeniya 20400, Sri Lanka. E-mail: kushant[at]pdn.ac.lk
Santalum album has received much attention during the recent years in Australasia due to its potential as a valuable NTF species. Sandalwood oil is used to prepare expensive perfumes, cosmetics and a range of medicines. One kg of Sandalwood oil is currently traded around US$ 3,000. The potential exists to reduce harvesting pressure on natural stands of S. album by establishing plantations. Around 80% germination was obtained when seeds were treated with 750 ppm gibberellic acid. When the seedlings were grown in equal parts of sand, soil and farm yard manure, a significantly greater (p<0.001) height, root collar diameter and leaf number were obtained. A significantly higher (p<0.01) performance of sandalwood seedlings, with respect to light, was observed between 25% - 50% (1300 _ 915 _ mol m-2 s-1) shade and with respect to the pot hosts, with Mimosa pudica and Tithonia diversifolia. The best growth in terms of plant height, root collar diameter, root biomass, over a 3 year field establishment trial was obtained in the treatment where a sandalwood plant was surrounded by four Sesbania grandiflora plants at a spacing of 1.5 m apart from each other. Field studies showed the potential of a range of native host plants that could be intercropped with Sandalwood. This improves the enhancement of natural biodiversity, creation of new habitats and conservation of plant species in degraded areas. All this would not have occurred with out a commercial incentive to growers, which in this case is Sandalwood.
Thorogood, CJ (1), Rumsey, FJ (2), and Hiscock, SJ (1)
Speciation and Host Specificity in Orobanche
1. School of Biological Sciences, University of Bristol, Woodland Road, Bristol, BS8 1UG, U.K.
E-mails: chris.thorogood[at]bristol.ac.uk, Simon.Hiscock[at]bristol.ac.uk
2. Natural History Museum, Cromwell Road, London SW7 5BD, UK. E: mail: .rumsey[at]nhm.ac.uk
Orobanche (broomrapes) are obligate parasites which attach to the roots of other plants as seedlings. Each species has a preferred host-range and while some species parasitize variety of plants, others are much more host-specific. It is possible that speciation in parasitic plants, like Orobanche, might be triggered by a shift in host preference. Continued divergence between parasite populations could then be driven by ecological isolation and/or selfing. We speculate that changes in host preference could be triggered by hybridization if hybrids possessed transgressive phenotypes that pre-adapted them to parasitism of a new host. We are investigating this hypothesis by studying an Orobanche complex in the UK in which two species, O. minor and O. picridis merge, and intermediate morphotypes, possibly hybrids between them, occur. The parent species' distributions are restricted to where their preferred hosts occur, while putative hybrids appear to occupy a new niche on coastal turf. Preliminary Inter-simple sequence repeat marker data shows evidence of introgression, suggesting that intermediate morphotypes are hybrids. We are also using rhizotrons (a bioassay in which host and parasite are cultivated) to investigate the host preferences of O. minor, O. picridis and the putative hybrids to determine whether hybridization can cause a change in host preference. Ultimately our goal is to determine whether hybridization and shifts in host specificity contribute to speciation in parasitic plants.
Timko, MP (1),Gowda, BS (1), Li, J (1), and Lis, K (1),
Deciphering the Interaction of Striga with Hosts and Non-hosts
1. Department of Biology, University of Virginia, Charlottesville, VA 22904 USA
The parasitic weeds Striga gesneroides (witchweed) and Alectra vogelii are among the major constraints to the production of cowpea, Vigna unguiculata (L.) Walp., one of the most important food and forage legumes in the semi-arid tropics of West and Central Africa. There is considerable variation in host specificity among isolates of S. gesnerioides. Based on host differential response and genetic diversity analysis at least seven races of S. gesnerioides have been identified within the cowpea-growing regions of West Africa that specifically parasitize cowpea. Similar evidence also exists for multiple races of A. vogelii parasitic on cowpea. Race specific resistance genes have been identified and mapped into two linkage groups (LG1 and LG6) within the cowpea genetic map. How race specific resistance is mediated at the cellular and molecular level remains to be determined. Studies are underway aimed at identifying the factors that determine host specificity and virulence in parasitic angiosperms and to address whether specific avirulence genes exist in S. gesnerioides that correspond to the race-specific resistance genes identified in cowpea and if these form the basis for a gene-for gene interaction as recognized in other plant-plant pathogen interactions. Our findings indicated that developmental processes occurring post-germination and attachment are likely more important in limiting successful host parasite interaction. Progress in this work will be discussed.
Tomilov, A (1), Tomilova, N (1), Filappova, T (1), Gunathilake, P (1), Wu, D-Y (1), Hoang, N (1), and Yoder, JI (1)
Early Haustorium Development in Triphysaria: A View from Inside the Nucleus.
1. Department of Plant Sciences, Mail Drop 3, University of California-Davis, Davis, California 95616-8780, USA style="color: windowtext;">jiyoder[at]ucdavis.edu
The competence to develop invasive haustoria is the defining feature of all parasitic species. We are identifying genes in the root parasite Triphysaria that are responsible for haustorium development in order to understand the evolutionary origin of this pathway in Orobanchaceae. In the longer term we are interested in learning the degree to which similar genetic pathways have been recruited in other parasitic families. Working under the assumption that genes associated with haustorium development will be differentially regulated soon after contact with a host root, we made cDNA libraries representing transcripts expressed in Triphysaria root tips after treatment with natural and chemical haustorial inducers. Nucleic acid hybridizations were performed to enrich the libraries for transcripts either up or down regulated after treatment with host roots, host root exudates, or purified haustorial inducing chemicals. These enriched libraries, as well as a library of cDNAs enriched for full length transcripts, were sequenced by the DOE Joint Genome Institute. Sequences of the ESTs and assembled unigenes are available as Fasta files at http://www.plantsciences.ucdavis.edu/yoder/lab/Sequence_index.html. Based on the distribution of transcripts in different libraries and on annotations of their putative functions, we selected a subset of genes for analysis by cDNA arrays. Candidate genes isolated on the basis of their expression profiles are being subcloned into RNAi vectors and introduced in Triphysaria roots by infection with Agrobacterium rhizogenes to monitor their functions in planta. Results and status of this work will be discussed.
van der Kooij,TAW (1,2), Krupinska K (1), and Krause, K(1,3)
Characterization of the Tocochromanol Content and Composition of Different Species of the Parasitic Flowering Plant Genus Cuscuta
1. Institute of Botany, Plant Cell Biology, Christian-Albrechts-University, 24098 Kiel, Germany E-mail: kkrupinska[at]bot.uni.kiel.de
2. Present address: HZPC research, P.O. Box 2, 9123 ZR Metslawier, Netherlands.
3. Present address: Institute for Biology, University of Troms, 9037 Troms, Norway. E-mail: kirsten.krause[at]ib.uit.no
The holoparasitic plant genus Cuscuta comprises plant species with different degrees of plastid functionality, ranging from intact photosynthetically active chloroplasts, via plastids with impaired protein production and gene expression to plastids with reduced plastome gene content. While some species are photosynthetically active and have a chlorophyll and carotenoid composition similar to non-parasitic plants, other species are non-photosynthetic and do not contain any chlorophyll. To investigate whether the tocochromanol content and composition is related to the photosyn_thetic capacity of the species, the overall content of tocochromanols and the levels of the individual tocochromanols were determined in stem sections of eight Cuscuta species. All species including the non-photosynthetic ones contain plastoquinone and tocochromanols at variable levels. In addition, unusual tocochromanol species were detected in C. japonica and C. grandiflora. No correlation between tocopherol content and carotenoid content or chlorophyll content was observed indicating a function of the tocopherols unrelated to antioxidative tasks.
Virupakshaiah, DBM (1), Ameresh, SH (1), and Mirji, SB (1)
Structure Analysis of Computer Generated Homologous Models of pm3 Protein in Triticum aestivum (Wheat)
1. Depart of Biotechnology, Basaveshwar Enineering College, S.Nijalingappa Vidhyanagar, Bagalkot-587 102, Karanataka, India, Post Box No: 53, Phone: 08354-234060, Fax: 08354-234204, E-mail: veerudbm1[at]rediffmail.com
Most of the plant protein structures have not been structurally characterized.(either by NMR or X-ray crystallography). In our research we made an effort to generate computer built model for powdery mildew resistant protein(f allele) found in Triticum aestivum (bread wheat) cultivar, michigan amber and also find homologous models to this protein. This protein is also called as pm3f protein and belongs to a group of pathogenesis related (pr) proteins. Structural analysis of this protein and its homologous models can help in studying their interaction with the target macro molecules in the attacking fungi with advent of artificial gene synthesis technique, the information retrieved from such a structural analysis can help in cloning and gene transfer experiments in those wheat cultivars which lack the resistance to powdery mildew.
Wegmann K (1)
2000 Years of Observation, Knowledge and Research on Orobanche
1. Center of Molecular Biology of Plants, University of Tuebingen, Auf der Morgenstelle 5, D-72076 Tuebingen, Germany E-mail: Wegmann[at]uvvg.ro
A historical survey will be presented on Orobanche, beginning with the first observations and descriptions, followed by the period of collecting and classification of Orobanche species in Linn's taxonomic system. Orobanche species have been collected in herbaria or they were preserved in alcohol (Racovita in Romania). Orobanche species up to date would have remained botanical curiosities among the wildflowers, if not some of them turned aggressive and became agricultural pests. The aim of Orobanche control became the driving force for intensive agricultural research. Agricultural problems also led to the organization of special Orobanche workshops besides the International Parasitic Weeds Symposia. When plant physiologists and plant biochemists became interested in Orobanche /host systems and Orobanche development increasing complexity became evident. Important steps in revealing the sophisticated systems will be emphasized, some problems in understanding Orobanche life will be pointed out. Moreover, the question will be asked, why most Orobanche species die back and need to be protected, why they have not become agricultural pests. What is the future of Orobanche research?
Williams, AM (1), and Virtue, JG (1)
Calculation of Growing Degree Days to Determine Optimum Timing of Herbicide Application for Control of Branched Broomrape Orobanche ramosa in Pastures.
1. Department of Water Land and Biodiversity Conservation, South Australian Government, GPO Box 2834, Adelaide, South Australia 5001. E-mail: williams.anna[at]saugov.sa.gov.au virtue.john[at]saugov.sa.gov.au
In South Australia (SA), branched broomrape Orobanche ramosa is the subject of a national eradication program. Inspections, quarantine protocols and control treatments are in place for affected properties in the Murray Mallee region of SA to limit any further spread of branched broomrape and eliminate soil seedbanks in mapped infestations. At present the weakest link in the eradication program is the difficulty of controlling branched broomrape in pasture paddocks. The pastures in the area are generally unimproved and contain a range of host species of branched broomrape. Management of branched broomrape in pastures is difficult but can be achieved by spraying sulfonylurea or glyphosate herbicides onto weed hosts prior to broomrape emergence. The timing of herbicide sprays is important to target smaller attachments.
Assessment of the timing of broomrape attachments and development until emergence was conducted in the field during the 2006 season. Additionally, observations were also collected on hosts grown in a glasshouse. The broomrape development data was correlated to growing degree days (GDD) using soil temperature and a base temperature of 0oC. Broomrape attachments began around 500 GDD after the start of the growing season, or after planting the hosts in the glasshouse. Emergence occurred 1000 GDD after attachment both in the glasshouse and in field conditions. Based on 2006 results, optimum herbicide application time would have been from 250 GDD after attachment to approximately 750 GDD after attachment. Further field and glasshouse observations are being conducted during 2007 to determine if the GDD model can accurately predict broomrape emergence in a different season and on different hosts.
Xie, X (1), Awad, AA (1), Yoneyama, K (1), Sekimoto, H (2), Kusumoto, D (1), Takeuchi, Y (1), Yoneyama, K (1)
Qualitative and Quantitative Differences of Strigolactone Exudation Determine Host Specificity of Root Parasites Orobanche and Striga
1. Weed Science Center, Utsunomiya University, 350 Mine-machi, Utsunomiya, 321-8505, Japan. E-mail: xmoonlighter[at]hotmail.com, aymanalawad[at]hotmail.com, fragrance0917[at]yahoo.co.jp, kusumoto[at]cc.utsunomiya-u.ac.jp, takeuchi[at]cc.utsunomiya-u.ac.jp, yoneyama[at]cc.utsunomiya-u.ac.jp.
2. Department of Plant Science, Faculty of Agriculture, Utsunomiya University, 350 Mine-machi, Utsunomiya, 321-8505, Japan. E-mail: hitoshis[at]cc.utsunomiya-u.ac.jp.
Strigolactones, originally identified as germination stimulants for root parasitic weeds, Striga, Alectra, and Orobanche, are now recognized as important chemical signals for arbuscular mycorrhizal (AM) fungi symbionts. Even non-mycotrophic plants like spinach exudes strigolactones, indicating that strigolactones may have some other important functions in plants and/or in rhizosphere communities. In addition, plants appear to exude mixtures of strigolactones along with other unknown germination stimulants, probably including non-strigolactones. It is likely that the amounts and composition of these stimulant mixtures may vary with plant species, their growth stages, and their growth conditions including nutrient availability. Furthermore, for example in sorghum, different cultivars exude different mixtures of strigolactones. These results suggest that quantitative and qualitative differences of strigolactones have some effects on host recognition by AM fungi and root parasitic weeds. Examples of qualitative and quantitative differences of strigolactones among host and non-host plants will be presented and discussed in relation to host-recognition by AM fungi and root parasites.
Yonli, D (1), Traoré, H (1), Sérémé, P (1), Hess, DE (2), and Sankara, P (3)
Integrated Striga hermonthica Management Based Fusarium
1. Institut de l'Environnement et de Recherches Agricoles, 04 BP 8645, Ouagadougou 04, Burkina Faso. E-mail: yonlidjibril[at]yahoo.fr or djbril_yonli[at]univ-ouaga.bf
2. Merry Lea Environmental Center of Goshen College, P.O. Box 263, Wolf Lake, IN 46796, USA.
3. Université de Ouagadougou, Unité de formation et de recherche en sciences de la vie et de la terre B.P. 7021, Ouagadougou, Burkina Faso.
Cereal production is mortgaged by Striga hermonthica (Del.) Benth., the main angiosperm root parasitic. The pathogenicity of endogenous Fusarium isolates against S. hermonthica was evaluated in the laboratory and an application method was investigated under greenhouse conditions. Cultural control methods against the parasitic plant were also evaluated under field conditions in order to combine them with biological control using Fusarium in Sorghum field. The results of our study showed that the spores and lyophilized culture filtrate of some Fusarium isolates significantly reduce germination of S. hermonthica seeds. Furthermore, applying spores from Fusarium isolates to the seeds of S. hermonthica led to a potential reduction of the germination rate of Striga of more than 78% with eight Fusarium isolates. The effectiveness of the lyophilized culture filtrate to inhibit germination of S. hermonthica is related to the amount and type of isolate used in the experiment. Thus, the complete inhibition of germination is observed starting from 33 mg/ml with the lyophilisate of four Fusarium isolates and at 67 mg/ml with that of three others. This study showed the capacity of Fusarium spores to kill S. hermonthica. Application of spores of two Fusarium isolates on the plants of the parasite led to a reduction of more than 77% of S. hermonthica dry biomass. Two substrates were used to produce the inoculum-based Fusarium: compost and Sorghum chopped straws. Incorporating the inoculum into the soil to control S. hermonthica was effective. By using this method, six Fusarium isolates showed potential effectiveness in controlling S. hermonthica. However, their effectiveness depends on the growth medium. Burial of S. hermonthica seeds up to 10 cm from the sowing hill containing the inoculum did not influence the performance of Fusarium isolates to control S. hermonthica. On the other hand, burial depths of 10 cm below the sowing hill containing the inoculum influenced the effectiveness of Fusarium isolates. Irrespective of the substrate, the increase of the burial depth led to a reduction of the number of Fusarium isolates effective against Striga. The evaluation of the pathogenicity of Fusarium isolates in field revealed the possibility to integrate biological control to cultural control methods in the management of S. hermonthica. The incorporation of inoculum-based compost into the soil led to a great reduction of number of emerged S. hermonthica in plots. Integrated management of S. hermonthica combining use of Fusarium, a tolerant Sorghum variety, trap crops or organic/mineral fertilizer reduced more significantly infestation of S. hermonthica in the field and subsequently enhanced crop yield. Results from these experiments of different control methods against S. hermonthica enabled us to propose an integrated management approach of the parasitic plant. However, there is need for improved bioherbicide formulations and delivery systems to enhance the potential role of biocontrol in integrated management of the parasite in Burkina Faso.
Yoneyama, K (1), Sekimoto, H (2), Takeuchi, Y (1), and Yoneyama, K (1)
Nitrogen and Phosphorus Deficiencies Promote the Production and Exudation of 5-Deoxystrigol in Sorghum
1. Weed Science Center, Utsunomiya University, 350 Mine-machi, Utsunomiya 321-8505, Japan E-mail: fragrance0917[at]yahoo.co.jp, takeuchi[at]utsunomiya-u.ac.jp, yoneyama[at]utsunomiya-u.ac.jp
2. Faculty of Agriculture, Utsunomiya University, 350 Mine-machi, Utsunomiya 321-8505, Japan. E-mail: hitoshis[at]utsunomiya-u.ac.jp,
Strigolactones secreted from plant roots are important host recognition signals for root parasitic weeds and symbiotic arbuscular mycorrhizal (AM) fungi. In red clover, a host of Orobanche, a reduced supply of phosphorus, but not of nitrogen or other mineral nutrients, significantly promoted the exudation of orobanchol. By contrast, deficiency of nitrogen as well as phosphorus markedly promoted the exudation of 5-deoxystrigol from sorghum, a host of Striga. When sorghum plants were subject to deficiency of both nitrogen and phosphorus, the exudation of 5-deoxystrigol increased only slightly as compared to those under phosphorus deficiency. Sorghum plants continuously exuded 5-deoxystrigol under nitrogen deficiency, but the exudation was suppressed within 24 h after adding nitrogen to the growth media. Similar results were obtained with phosphorus treatments. Nitrogen and phosphorus deficiencies also increased 5-deoxystrigol contents in sorghum roots. In both cases the increase was comparable to that in the root exudates. These results suggest that strigolactones may be released rapidly after their production in the roots. Unlike the situation in the roots, nitrogen and phosphorus deficiencies did not increase the trace amounts of 5-deoxystrigol that are found in sorghum shoots.
Yoshida, S (1), and Shirasu, K (1)
Agrobacterium-Mediated Transformation of Striga hermonthica
1. Plant Science Center, RIKEN, 1-7-22 Suehiro-cho, Tsurumi, Yokohama, 230-0045 Japan, E-mail: satokoy[at]psc.riken.jp, ken.shirasu[at]psc.riken.jp
Striga spp. (witchweeds) are major agricultural pests which infest important crops in sub-Saharan Africa and parts of Asia. To develop control methods against Striga infestation, understanding the molecular basis underlying its parasitism is of particular importance. However, molecular knowledge about Striga infection is still limited. Reverse genetic approaches are powerful tools to assess unknown gene function and identify functional genes. Establishment of a transformation system is a critical step to conduct reverse genetic experiments. In the present study, we aim to establish transformation methods of Striga hermonthica using Agrobacterium. Striga is an obligate root parasite which is unable to live without its host in natural conditions. Therefore we initially developed axenic culture conditions of S. hermonthica. Surface sterilized S. hermonthica seeds were germinated and grown under axenic conditions. Striga plants were able to develop plant architecture with shoots and root-like structures in the presence of sufficient nutrients and carbon source in the media. Callus formation and emergence of shoot and root-like structures were controlled by a balance of auxin and cytokinin. We tested transformation of aseptically grown S. hermonthica via Agrobacterium tumefaciens or A. rhizogenes using green fluorescence protein (GFP) as a marker. Our preliminary results showed that A. rhizogenes-mediated transformation successfully generated GFP expressing hairy roots of S. hermonthica.