Differences in virulence of Phytophthora capsici isolates from a global collection
L. GRANKE (1), L. M. Quesada-Ocampo (1), M. Wood (1), J. Olsen (1), M. Mercier (1), M. Hausbeck (1)
(1) Michigan State University, East Lansing, MI, U.S.A.
Phytopathology 101:S63

Phytophthora capsici causes root, crown, and fruit rot of vegetable and tropical hosts. Cucumber, zucchini, tomato, and pepper fruits were inoculated using 6-mm-diameter agar plugs of P. capsici, incubated in clear plastic boxes at room temperature (~26°C and 100% relative humidity), and virulence was estimated by measuring the lesion diameter three (cucumber, zucchini) or four (tomato, pepper) days later. When isolates were grouped by genetic cluster, differences in virulence were observed for cucumber and zucchini. On tomato, no significant differences were observed for isolates grouped by genetic cluster, but isolates from vegetable crops were generally more virulent than isolates from tropical hosts. No significant differences in lesion diameter were noted on pepper when isolates were grouped by host family of origin or genetic cluster membership. Our findings suggest that isolate characteristics such as host family of origin and genetic cluster membership may be used to guide initial isolate selection for cucurbit fruit resistance screening. Final isolate selection should incorporate the phenotypic and genetic diversity of P. capsici, including isolates with differing virulence to the host organ of interest.