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Effect of Soil Temperature and Moisture on the Survival of Mucor piriformis. Themis J. Michailides, Former graduate research assistant, Department of Plant Pathology, University of California, Davis 95616; Joseph M. Ogawa, Professor, Department of Plant Pathology, University of California, Davis 95616. Phytopathology 77:251-256. Accepted for publication 17 July 1986. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/Phyto-77-251.

Temperature was a more important factor than moisture in affecting survival of sporangiospores of Mucor piriformis [California isolate (CA), Chile isolate (CH)]. In a Reiff loam soil, sporangiospores showed longest survival at 0 and 21 C and least survival at 36 and 39 C. Sporangiospores survived better in dry (1,300 bars matric potential) than in wet (0.3 bar matric potential) or wet-dry soil (0.3 to 1,300 bars matric potential) at all temperatures except 0, 36, and 39 C. Viability of propagules (mycelia and spores) of M. piriformis mixed with soil and buried 5 and 10 cm deep in this soil at Davis, and in a Hanford fine sandy loam at Parlier, CA, declined over time in an exponential fashion. At Davis, where weekly mean temperatures of soil were lower than 27 C, spores of both isolates survived up to 1 yr. In contrast, at Parlier, where weekly mean temperatures of soil were higher than 27 C, the decline of propagule viability was faster and only the CA isolate buried at 10-cm depth survived for a year. Similarly, on inoculated and mummified peaches buried 5 cm deep in soil, the CA isolate was recovered after 1920 mo at both locations and the CH isolate after 9 and 20 mo, respectively, for Parlier and Davis locations. Microscopic observation of colonies of M. piriformis from propagules surviving a year in soil revealed that all colonies originated from sporangiospores. Mycelia buried in soil survived 40 and 21 days under laboratory and field conditions, respectively.

Additional keywords: moisture, nectarines, peaches, postharvest pathogen, soil, temperature.