Survival ofPhytophthora infestansin Seeds Extracted from Infected Tomato Fruits

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Abstract
Seeds were extracted from healthy and blighted tomatoes collected from 3 field-grown cultivars, processed as in a commercial operation, and the seeds plated on a selective medium, P. infestans usually was isolated (avg [average] 91.7%) from discolored, freshly extracted, wet seeds but not from discolored seeds that had been derived in an oven (29.5-37.5.degree. C) for 6 h or air-dried for 72 h following extraction. Fermentation for 24 h eliminated the fungus from discolored seeds of cultivar 7718 but not from discolored seeds of cultivar Castle 1025 or those of an unidentified cultivar of cherry tomato. Treatment of wet, discolored seeds with either NaOCl (0.5% for 5 min) for 0.12 N HCl (pH 1.6, for 25 min) significantly reduced the frequency of isolation. In discolored seeds, hyphae were observed on and in the seed coat, in the remnants of the funiculus, and between the endosperm and the seed coat. When freshly extracted, wet or dried discolored seed were planted in steamed UC soil mix or in field soil in the greenhouse, some of the seedlings emerging from wet seeds were infected (avg 26%), whereas seedlings emerging from dry seeds were healthy. Infected tomato fruits placed in the field on a wet soil surface or plowed under and kept continuously wet by irrigation occasionally gave rise to infected seedlings.