Variation in Phenotypic Characteristics of Phytophthora capsici Isolates from a Worldwide Collection

Granke, L. L., Quesada-Ocampo, L. M., and Hausbeck, M. K. 2011. Variation in phenotypic characteristics of Phytophthora capsici isolates from a worldwide collection. Plant Dis. 95:1080-1088. To determine variation within Phytophthora capsici, 124 P capsici isolates from 12 countries were characterized for sporangial length and width, pedicle length, oospore diameter, sporangia and chlamydospore production, and growth at 32, 35, and 38 C. Sporangia were 23 to 35 pm wide and 38 to 60 pm 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 pm long) varied widely among isolates; differences were apparent by continent and host family of origin. Oospore diameters varied among isolates (22 to 37 pm), but no differences were noted by isolate genetic cluster, host family of origin, continent of origin, mating type, or sensitivity to mefenoxam. Differences in sporangia production were observed among isolates grouped by continent, and isolates from non-vegetable hosts produced fewer sporangia than isolates from vegetable hosts. When cultures were incubated in a liquid medium, 35 P capsici isolates formed chlamydospores. Most (122 of 124) of the isolates were able to grow at 35 degrees C, but all of the isolates grew poorly at 38 degrees C. The results of this study indicate substantial variation in morphological and physiological characteristics among P capsici isolates.