Euro. J. Plant Pathol. DOI:10.1007/s10658-011-9873-4 Online First Differences in virulence of Phytophthora capsici isolates from a worldwide collection on tomato fruits Dr. Leah Granke Dr. Lina Quesada-Ocampo Dr. Mary Hausbeck October 13, 2011 Department of Plant Pathology
Vegetable hosts of P. capsici P. capsici is distributed worldwide Causes root, crown and fruit rot of tomato and other vegetables (cucurbits, snap and lima bean, eggplant) Also, tropical hosts (macadamia, cacao, black pepper) In Michigan, susceptible vegetables are worth at least $160 million Tomato $30+ million ミ http://www.nass.usda.gov/quickstats/ Quesada-Ocampo
Management Challenges Long-term survival of oospores in the soil Long-distance spread via irrigation water and human activity (movement of equipment and cull fruits) Growing list of susceptible hosts Lamour Quesada-Ocampo Limited number of fungicides that provide effective control Lack of commercially acceptable resistant cultivars
Differences in virulence in P. capsici 12889 OP97 SP98 SFF3 Quesada Rodriguez 12889 OP97 12889 OP97 SP98 Enzenbacher 12889 OP97 SP98 Enzenbacher Gevens Enzenbacher Enzenbacher SP98 SFF3 12889 OP97 SP98 Enzenbacher 12889 OP97 SP98 Enzenbacher Enzenbacher 12889 12889 OP97 OP97 SP98 SP98 SFF3 Quesada Foster SFF3 Foster
Population structure of P. capsici isolates from a worldwide collection L. M. Quesada-Ocampo, L. L. Granke et al., Phytopathology 101:1061-1073 Classified 236 isolates in clusters using 10 sequenced genes Clusters are not evidence of physiological race since we did not include virulence data Previous study (Islam et al. 2004) found virulence groups corresponded directly with RAPD groups
Is virulence associated with other isolate characteristics? Geographic origin Host family of origin Genetic cluster membership Can we use isolate characteristics to guide isolate selection for host resistance screening?
Differences in virulence of Phytophthora capsici isolates 126 P. capsici isolates 12 countries (Cameroon, Italy, Japan, Korea, Mexico, Norway, Peru, Spain, Taiwan, Thailand, Uruguay, and United States) 6 host families (Cucurbitaceae, Solanaceae, Fabaceae, Piperaceae, Proteacae, Sterculiaceae) 17 host species
Estimating virulence on fruits 0 1 2
Results: geographic origin Lesion diameter (cm) 8 7 6 5 4 3 2 1 0 ab a a ab b N. America (93) Asia (18) S. America (6) Europe (8) Africa (1) Differences in isolate virulence by geographic origin was minimal The one African isolate (red cluster, cacao) was less virulent than isolates from other continents
Pathogen diameter (cm) 6 5 4 3 2 1 0 N. America (93) Asia (18) S. America (6) Europe (8) Africa (1) Sporulation density (0-2) 2 1.5 1 0.5 0 N. America (93) Asia (18) S. America (6) Europe (8) Africa (1) No significant differences in pathogen growth and sporulation by geography
Results: host family of origin Lesion diameter (cm) 6 5 4 3 2 1 0 a Solanaceae (64) ab Cucurbitaceae (46) a Fabaceae (12) ab Piperaceae (2) ab Proteaceae (2) b Sterculiaceae (1) No significant differences between isolates from vegetable crops Isolates from vegetable crops more virulent than isolates from tropical hosts
Pathogen diameter (cm) 6 5 4 3 2 1 0 Solanaceae (64) Cucurbitaceae (46) Fabaceae (12) Piperaceae (2) Proteaceae (2) Sterculiaceae (1) Sporulation density (0-2) 2 1.5 1 0.5 0 Solanaceae (64) Cucurbitaceae (46) Fabaceae (12) Piperaceae (2) Proteaceae (2) Sterculiaceae (1) No significant differences by host family Isolates from vegetable crops grew and sporulated better than isolates from tropical hosts
Results: Genetic clusters 1.0 0.8 0.6 0.4 0.2 0.0 Lesion diameter (cm) No direct correspondence between virulence and genetic cluster Some clusters were more likely to yield virulent isolates Purple, blue, and dark green clusters=large lesions Other clusters showed a range of response Red cluster isolate=small lesions
1.0 0.8 0.6 0.4 0.2 0.0 1.0 0.8 0.6 0.4 0.2 0.0 Pathogen growth diameter (cm) Sporulation density (0-2 visual scale) No direct correspondence between growth and genetic cluster Dark green cluster=good growth and sporulation on fruit Red cluster=no growth or sporulation
Summary No obvious differences by geography Isolates from vegetable crops were generally more virulent than isolates from tropical hosts Bean isolates are highly virulent No direct correspondence between clusters and virulence Isolates from purple, blue, and dark green clusters generally were more virulent Variation within P. capsici Robust host screening should include isolates that represent the variation within P. capsici
Acknowledgements Many colleagues and growers that shared samples with us Hausbeck Lab: Lina Quesada-Ocampo Amy Lebeis Mitch Wood Ronnie Heslip Funding: Michigan State Uni. Agriculture Experiment Station USDA Cooperative State Research, Education, and Extension Service USDA Specialty Crop Research Initiative