Effect of Temperature During Conidial Formation of Monilinia laxa on Conidial Size, Germination and Infection of Stored Nectarines

Conidia of Monilinia laxa produced at different temperatures were studied for size and germinability, and for their pathogenicity to nectarine fruits kept in refrigerated storage at 0°C. The mycelial growth, which was evaluated on peach‐agar at temperatures ranging from 25 to −4°C, decreased with temperature and ceased at −4°C. When the temperature was lowered from 25 to 0°C, the conidia volumes increased by 41% on peach‐agar and by 15.5% on nectarines. The conidia germinated at the temperatures tested from 20 to −4°C. At germination temperature from 10 to −4°C, larger conidia produced at 0 and 5°C germinated earlier with longer germ tubes than those produced at 25°C. But when incubated at 20°C the conidia produced at 0°C germinated later or at the same time as those produced at 25°C and formed shorter germ‐tubes. Conidia produced at the lower temperatures (0 and 5°C) and inoculated onto wounded nectarines stored at 0°C, were highly infective and infectivity decreased when the conidia were produced at 25°C. The differences were particularly evident at the lower conidium suspension concentration (5 × 10 2 and 2 × 10 3 conidia ml −1). After 4 weeks 30–50% of the nectarines had rotten when the inoculation was carried out with spores at the concentrations of 5 × 10 2 and 2 × 10 3 conidia ml −1 and produced at 0°C, while the fruits infected with spores produced at 25°C were all still sound.