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Existence of Chlamydospores of Alternaria porri f. sp. solani as Overwintering Propagules in Soil. P. K. Basu, Plant Pathologist, Ottawa Research Station, Canada Department of Agriculture, Ottawa; Phytopathology 61:1347-1350. Accepted for publication 4 June 1971. DOI: 10.1094/Phyto-61-1347.

Dark brown, thick-walled, more or less round chlamydospores formed in the “curly type” mycelium of Alternaria porri f. sp. solani within infected tomato tissues as well as in agar cultures. These varied in diameter from 8 to 15 µ, and occurred in chains, in clusters, or singly. Similar round, thick-walled cells also formed in normal conidia placed in natural soil. These propagules overwintered in soil, with or without host tissues, through soil and air temperatures ranging from –3.3 to 21.1 C and –31.1 to 27.7 C, respectively, for 7 months or more, and caused primary infection to the next crop.