Intraspecific Variation Among Isolates ofPhytophthora capsicifrom Pepper and Cucurbit Fields in North Carolina

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Abstract
Phytophthora capsici was isolated from seven pepper and seven cucurbit field in North Carolina. The relative virulence of the isolates was tested on pepper (Capsicum annuum), morphological characteristics of sporangia and oospores were evaluated, and mating type and growth response to temperature was determined. All pepper and some cucurbit isolates of P. capsici were highly virulent on pepper, whereas other cucurbit isolates were less virulent on pepper. Sporangia of cucurbit isolates were greater than 55 .mu.m in length and were less variable in length than sporangia of pepper isolates. Pedicel lengths of sporangia ranged from 31 to 99 .mu.m and were highly variable among isolates from both hosts. Oospore diameters ranged from 24 to 35 .mu.m among isolates. The potential exists for sexual recombination and oospore formation to occur in some fields in the state, because both mating types were present in two of 14 fields samples. None of the isolates produced chlamydospores in culture. A culture from the ATCC and other isolates grew slowly or not at all at 36 C; therefore, growth at temperatures greater than 35 C was not a definitive character for identification of isolates of P. capsici. Continuous rather than discrete variation was observed in sizes of sporangia, pedicels, and oospores based on host.