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Oral: Pathogen Diversity


Characterization of isolates of Phytophthora capsici from the mid-Atlantic region, US.
N. ABEYSEKARA (1), H. Hickman (2), S. Westhafer (2), N. Gregory (2), G. Johnson (2), T. Evans (2), N. Donofrio (2) (1) University of Delware, U.S.A.; (2) University of Delaware, U.S.A.

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The heterothallic oomycete Phytophthora capsici causes disease under warm (25-28oC), wet conditions. This pathogen causes pod rot in lima bean (Phaseolus lunatus L.), an emerging disease in the mid-Atlantic region which reduces yields and limits production. In order to better understand sources of inoculum, isolates were collected from infected commercial plant samples, 13 irrigation water sources, potential weed hosts, and soil sediments in Delaware. Water filtration, baiting with fruits, or baiting with Rhododendron leaves, were used in an attempt to extract P. capsici from irrigation water. Species other than P. capsici were recovered in abundance from irrigation water, weed hosts, and soil sediments. A total of 38 isolates were recovered from symptomatic lima bean, pepper, pumpkin, and watermelon samples and positively identified as P. capsici both morphologically and molecularly. Isolates derived from single zoospores where characterized for mating type, mefenoxam sensitivity and virulence on eight commercial lima bean cultivars. The A2 mating type was prevalent among the collected isolates (78.9%) and seven isolates with resistance to mefenoxam were identified. All isolates were virulent on the eight lima bean cultivars tested. Two SSR markers were identified that co-segregate with mefenoxam sensitivity, with over 80% accuracy when used together, that could have potential use in disease management efforts.