Department of Plant Pathology, Washington State University, Tree Fruit Research and Extension Center, 1100 North Western Avenue, Wenatchee 98801
Potebniamyces pyri is the causal agent of Phacidiopycnis rot, a postharvest disease of pears. Infection of fruit occurs in the orchard, and symptoms develop during storage. Conidial germination of P. pyri in response to nutrient, temperature, wetness duration, relative humidity (RH), and pH was determined in vitro. Conidia germinated by either budding or developing germ tubes in various concentrations of pear juice solutions. The mode of conidial germination was nutrient-dependent. Low nutrient levels favored budding, whereas high nutrient levels favored germ tube development. Conidia germinated at 0 to 30°C but not at 35°C, with optimum temperature between 20 and 25°C. Wetness durations of 4 to 5 h and 6 to 8 h at optimum temperature were required for budding and developing germ tubes, respectively, and 20 to 24 h of wetness was required to reach germination peaks. Regardless of temperature, conidia germinated primarily by budding in 10% pear juice. Secondary conidia, produced by budding of conidia, initially increased their dimensions and later germinated at 0 to 25°C in the same manner as mother conidia. No germination of secondary conidia occurred at 30°C. Germ tubes from conidia elongated at 0 to 25°C but not at 30°C. No germination occurred at ≤95% RH. At 20°C, conidia germinated only by germ tubes at 98% RH, and conidia germinated in both manners at 100% RH but dominated by germ tubes. In free water (0.1% pear juice) the majority of conidia germinated by budding. After 5 days at 0°C, conidia germinated at 100% RH but not at ≤98% RH. More than 80% of conidia germinated in 10% pear juice at pH 4 to 7 after 24 h at 20°C, whereas there was <50% germination at pH 3. Low pH favored budding, whereas high pH favored developing germ tubes. These results contribute to a better understanding of the biology and ecology of the fungus and environmental conditions required for infection of fruit.