บทคัดย่องานวิจัย

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Studies on the ecology and epidemiology of the postharvest fruit pathogen Mucor piriformis Fischer. I. Effect of temperature and moisture on the survival of propagules in soils. II. Colonization, sporulation, and persistence in orchard soils

Michailides, Themistocles John.

Ph.D., University of California, Davis, 1984, 101 pages.

1984

บทคัดย่อ

STUDIES ON THE ECOLOGY AND EPIDEMIOLOGY OF THE POSTHARVEST FRUIT PATHOGEN MUCOR PIRIFORMIS FISCHER. I. EFFECT OF TEMPERATURE AND MOISTURE ON THE SURVIVAL OF PROPAGULES IN SOILS. II. COLONIZATION, SPORULATION, AND PERSISTENCE IN ORCHARD SOILS.

Mucor piriformis Fischer, a postharvest pathogen of pome and stone fruit, and also of strawberries, can decay fruit in cold storage and at ripening temperatures.  Its occurrence in orchard soil indicates that the source of the fungus is the orchard soil; but its long-term survival structure, its longevity, and its saprophytic growth in soil is unknown.  This treatise, therefore, presents and discusses research on the effects of moisture and temperature on the survival of M.  piriformis propagules, determines its long-term survival structures, and investigates the saprophytic behaviour of the fungus in orchard soil.

 Sporangiospores of two M.  piriformis isolates (California CA and Chile CH isolate) were added to nonsterile orchard soil, held under laboratory conditions for various lengths of time, and sampled periodically to determine spore viability.  Temperatures of 0, 21, 27, 33, 36, and 39 C were used in combination with wet (20 g water/100 g dry soil), dry (initial moisture of 20 g water/100 g dry soil allowed to dry continuously), and alternately wet-dry soil (initial moisture of 20 g water/100 dry soil allowed to dry and initial level restored by periodic weighting and watering).  Survival was indicated by the forming of colonies by propagules on soil dilution plates.  Temperature was a more important factor than moisture in determining sporangiospore survival.  In a Reiff loam soil, sporangiospores showed the highest levels of survival at 0 and 21 C, the lowest at 36 and 39 C, and had intermediate levels at 27 and 33 C.  Sporangiospores survived better in dry than in wet or wet-dry soil at all temperatures exc

 ept at 36 and 39 C; at these high temperatures sporangiospores had a poor survival rate at all levels of moisture tested.

 Viability of M.  piriformis propagules mixed with soil and buried 5 and 10 cm deep in soil at Davis and Parlier, California, declined over time in an exponential fashion.  At Davis, where weekly mean temperatures of soil were lower than 27 C, the decline was slower and propagules of both isolates survived up to one year.  In contrast, at Parlier, where weekly mean temperatures of soil during the summers of 1982 and 1983 were usually higher than 27 C, the decline of propagules was faster and only the CA isolate buried at 10 cm depth survived for a year.  Similarly, on inoculated and mummified peaches that were buried intact 5 cm deep in soil, both CA and CH isolates were recovered after 20 months at Davis; at Parlier the CA isolate was recovered after 19 months but the CH could not be recovered after 9 months.  .  .  .  (Author's abstract exceeds stipulated maximum length.  Discontinued here with permission of author.) UMI.