Phytophthora capsici Leonion was first identified on pepper (Capsicum annuum L) in Taiwan in 1976. At that time, only the A1 mating type was present (2). In 2007, the A2 mating type of P. capsici was identified on tomato and eggplant in the central part of the country (1). During an excessively rainy period in mid-2008, many chili and sweet pepper fields in Taiwan suffered severe losses due to P. capsici. Symptoms included a foliar blight and stem, root, and fruit rot. Plants eventually wilted and died. Symptomatic plants were collected from chili- and sweet pepper-production areas in central, southern, and eastern Taiwan. Fifty-three isolates from single zoospores were identified by PCR using species-specific primers CAPFW/CAPRV2 (4). Mating type was determined by co-inoculating rape seed agar plates (3) with mycelial plugs of the tester and a known isolate. Pc134, maintained by the mycology unit at The World Vegetable Center, and 27220, provided by P. J. Ann at the Taiwan Agricultural Research Institute, were used as reference isolates of A1 and A2 mating types, respectively. Plates were examined microscopically for oospores after 5 to 7 days of incubation at 24°C in the dark. Of the 53 isolates, 15 were identified as the A2 mating type and the remaining 38 isolates were identified as A1. The A2 mating type was found in the central and southern regions while the A1 mating type was widely distributed across all three regions. The sporangia of the A2 mating type were 60.4 to 73.4 × 40.9 to 51.8 μm (average 69.2 × 44.7 μm), whereas sporangia of the A1 mating type were 50.1 to 73.9 × 37.9 to 48.1 μm (average 61.4 × 44.1 μm). In general, the A2 mating type produced longer sporangia and only a few isolates produced chlamydospores in V8 broth and on agar. To our knowledge, this is the first report of the A2 mating type of P. capsici infecting peppers in Taiwan. The presence of both mating types in the same field has been observed.
References: (1) P. J. Ann et al. Plant Pathol. Bull. 17:69, 2008. (2) L. S. Leu and C. W. Kao. Plant Prot. Bull. (Taiwan) 23:59, 1981. (3) M. M. Sautor. Mycologia 59:161, 1967. (4) C. Silvar et al. Eur. J. Plant Pathol. 112:43, 2005.
