Colonization and Sporulation of Phytophthora infestans on Volunteer Potatoes Under Western Washington Conditions
Gigot. J. A Gundersen. B Inglis. D. A
American Journal of Potato Research ; 2009 [Vol.86] Pages:1-14
Abstract
Growth, sporulation, and survival of Phytophthora infestans on volunteer potato tubers, was investigated under temperatures representative of winter (4°C, 7°C, and 10°C) and spring (13°C, 16°C, 19°C) soil conditions in western Washington. Inoculated tubers stored at 10°C for 8 days had a significantly (P < 0.05) higher percentage of disease symptoms on tuber surfaces and a higher number of lenticels and eyes with P. infestans sporulation compared to those stored at 4°C or 7°C. Sporulation of P. infestans on cut tuber surfaces was observed following 3-week storage at the three winter soil temperatures. After 12-week storage, tubers inoculated with a US-8 isolate had a significantly higher percentage of late blight on cut surfaces than those inoculated with a US-11 isolate (70% versus 50%, respectively). For spring soil temperature studies, tubers inoculated with the US-8 isolate and held at 19°C had a significantly higher number of lenticels per tuber with P. infestans sporulation than tubers held at 13°C or 16°C. Sporulation of P. infestans on tuber surfaces was detected on infected tubers buried 5-cm deep in potting medium at all tested winter and spring temperatures for 3- or 6-day periods, respectively. The site or depth of tuber inoculation with P. infestans did not influence tuber-to-sprout infection events and whether apical end or stem sprouts become infected. Tubers with late blight that survive the winter in western Washington and support sporulation of P. infestans via lenticels and eyes may enable the transmission of P. infestans from infected tissues to sprouts of volunteer plants. However, the impact of these events on primary inoculum production by P. infestans in the region is probably limited by the mild, winter conditions favoring tuber break-down in soil.
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