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Cold Inactivation of Phytophthora cinnamomi. D. M. Benson, Associate professor, Department of Plant Pathology, North Carolina State University, Raleigh 27650; Phytopathology 72:560-563. Accepted for publication 17 August 1981. Copyright 1982 The American Phytopathological Society. DOI: 10.1094/Phyto-72-560.

Mycelium of Phytophthora cinnamomi in cornmeal agar and chlamydospores in naturally infested soil were inactivated on a thermal gradient plate at temperatures below 0 C. Rate of inactivation was directly related to number of degrees below 0 C. Inactivation of mycelium of P. cinnamomi occurred in 2, 6, or 16 days, at 6.7, 3.8, and 1.4 C, respectively. In a sandy-loam soil, chlamydospores of P. cinnamomi were inactivated after 2, 17, or 29 days at 6.4, 3.4, and 0.5 C, respectively. Acclimatization of agar cultures or infested soil for 57 days at 4 C did not increase tolerance of P. cinnamomi to subzero temperatures. Inoculum of P. cinnamomi in infested root segments of Abies fraseri, in colonized oat grains, or in naturally infested soil, was inactivated during winters (19761977 and 19771978) when soil temperature at a depth of 10 cm dropped to 0 C or below, but not during the winter of 19751976 when soil temperatures remained above 0 C.