Global phenotypic variation in Phytophthora capsici
L. GRANKE (1), L. M. Quesada-Ocampo (1), A. Lebeis (1), L. Henderson (1), M. VanOverbeke (1), M. Hausbeck (1)
(1) Michigan State University, East Lansing, MI, U.S.A.
Phytopathology 101:S63

To determine global phenotypic variation, 124 P. capsici isolates from 12 countries were characterized for sporangial length and width, pedicle length, oospore diameter, sporangial and chlamydospore production, and growth at 32, 35, and 38°C. Sporangia were 23 to 35 µm wide and 38 to 60 µm long; differences in width and length were noted when isolates were grouped by genetic cluster and continent of origin. Length:breadth ratio (1.34 to 2.07) and pedicle length (20 to 260 µm long) varied widely among isolates; differences were apparent by continent and host family of origin. Oospore diameters varied among isolates (22 to 37 µm), but no differences were noted by isolate genetic cluster, host family of origin, continent of origin, mating type, or sensitivity to mefenoxam. Differences in sporangial production were observed among isolates grouped by continent, and tropical isolates produced fewer sporangia than isolates from vegetable hosts. When cultures were incubated in liquid medium, 35 P. capsici isolates formed chlamydospores. Growth at high temperatures did not reliably separate P. capsici from P. tropicalis in this study. The results of this study indicate that separation of P. capsici from closely related Phytophthora species based on morphological and physiological characters alone could be misleading.