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Phytophthora infestans transmitted to seedlings growing from tomato fruit rotted by late blight but not their seed.
M. T. MCGRATH (1). (1) Cornell University, Riverhead, NY, U.S.A.

Study impetus was outbreaks of late blight for which volunteer tomatoes or saved seed appeared to be possible pathogen sources. Fruit naturally infected with genotype US-23 were used. Fruit were held for 11 days after collecting, then put in potting mix in trays. Seedlings began emerging within 7 days in trays kept in a greenhouse. Late blight symptoms appeared on lower stems starting 13 days after planting in cultivar ‘Sweet Treats’, which emerged first. Asymptomatic seedlings were transplanted in groups into pots. Seedlings were removed as symptoms appeared. Last were on ‘Juliet’ 67 days after collecting fruit. Very few sporangia were observed on stems examined microscopically. Abundant sporulation developed on stems incubated in humid plastic bags and on cotyledons when infection progressed up stems reaching this tissue. A similar set of trays was kept cool and dark for 75 days to delay germination. Symptoms did not develop on any seedlings that grew in these trays after they were put in the greenhouse. Seed was removed from symptomatic fruit of ‘Mt Fresh Plus’ and ‘SunGold’. Some seed was planted immediately. Other seed was first either incubated for 8 or 15 days in the fruit’s juice, held dry for 65 days, rinsed in water before drying, or incubated in either water or soapy water for at least 4 days before drying. No symptoms were seen on the seedlings that grew. While <i>Phytophthora infestans</i> survived on fruit, it was not present or able to survive in or on tomato seed.<p><p>Keywords: Oomycete, Vegetables, Tomato

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