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Aggressiveness to Pumpkin Cultivars of Isolates of Phytophthora capsici from Pumpkin and Pepper

Nine isolates of Phytophthora capsici obtained from pumpkin and pepper in diverse geographic areas, including Korea, France, Italy, and the United States, were evaluated for their ability to cause disease on nine Korean and Japanese pumpkin cultivars under controlled environmental conditions. No hypersensitive type of resistance was observed in any of the pumpkin cultivars inoculated with P. capsici. Disease incidence ranged from low to high, indicating varying levels of partial (quantitative) resistance. In addition, a significant cultivar-isolate interaction was observed, indicating that host specialization was present in some cultivars. Disease severity increased with inoculum density of P. capsici. The Korean cultivar Danmatmaetdol was highly resistant to the P. capsici isolates tested, suggesting that economic levels of resistance exist in pumpkin. The pumpkin isolates from all locations caused more disease than the pepper isolates to all the pumpkin cultivars tested. Soil-drench and stem-wound inoculation methods were more reliable than a foliar-inoculation method for evaluating pumpkin cultivar resistance.