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Effects of High Temperatures on the Survival and Pathogenicity of Propagules of Mucor piriformis. Themis J. Michailides, Postdoctoral research associate VI, Department of Plant Pathology, University of California, Davis 95616, Present address: Department of Plant Pathology, University of California, Berkeley, Kearney Agricultural Center, Parlier, 93648; Joseph M. Ogawa, Professor, Department of Plant Pathology, University of California, Davis 95616. Phytopathology 79:547-554. Accepted for publication 8 November 1988. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/Phyto-79-547.

Survival of mycelia and sporangiospores of Mucor piriformis (California isolate [CA] and Chile isolate [CH]) were compared at temperatures of 3560 C. The thermal death points of the mycelia and sporangiospores were 46 and 55 C, respectively, for isolate CA and 43 and 52 C, respectively, for isolate CH. After a 2-day incubation at 27 C, both isolates exhibited yeast-like growth on agar medium. Sporangiospore germination was erratic at 27 C and, when subsequently incubated at 21 C, germ tubes were abnormally swollen and produced no viable colonies. Reduction in viability was greater in wet than in dry sporangiospores. Preincubation of sporangiospores in dry (1,300 bars matric potential) or wet (0.3 bar matric potential) soil at 27 or 33 C for 15 days followed by incubation at 21 C for 45 days resulted in significantly lower viability in both isolates than in sporangiospores incubated continuously at 21 C for 60 days at both water potentials. Preincubation of sporangiospores at 33 C for 15 days resulted in a faster decline in survival than preincubation at 27 C for 15 days followed by 21 C for 45 more days. Pear fruits wound-inoculated with M. piriformis and dipped in 47 C water for 30 min had 15% infected wounds, whereas fruits inoculated in the same way and dipped for 30 min in water at 21 C had 90% of the wounds infected. Results from this study suggest that hot water treatment of fruit may reduce inoculum levels and postharvest infection.

Additional keywords: Mucor decay, postharvest pathogen.