An investigation of biological attributes that may contribute to the importance of <i>Phytophthora capsici</i> as a vegetable pathogen in Florida

Abstract

Summary During the 1999–2000 and 2000–2001 seasons, 19 commercial squash fields in the vicinity of Homestead, Florida (USA) were examined for diseases caused by Phytophthora capsici . In each of the six fields in which two or more isolates of P. capsici were recovered, both the Al and A2 mating types were present, and both mating types were recovered from the same plant five times. Insensitivity to mefenoxam was common among isolates, with EC50s ranging from 5 μg mefenoxam ml −1 to more than 60 μg ml −1 . Of 15 weed species that were examined as possible alternative hosts of the pathogen, only common purslane, Portulaca oleracea , was infected by P. capsici . Few or no oospores of the pathogen formed in a glasshouse (c . 28°C) when artificially inoculated pepper plants were covered with plastic bags or kept under continuous mist. In studies in the laboratory (c . 22°C) with detached pepper leaves, no oospores were formed on wire screens over water reservoirs. Consistent production of oospores occurred only when leaves were in constant contact with water. Maximum production occurred at 18°C, and production also occurred at 14°C, 20°C, 24°C and 26°C, but not at 6°C, 12°C, 30°C and 32°C.