INFLUENCE OF TEMPERATURE ON APOTHECIAL DEVELOPMENT AND ASCOSPORE DISCHARGE BY BLUMERIELLA-JAAPII

Cherry leaves bearing apothecia of Blumeriella jaapii with either immature or mature asci were collected from a sweet cherry (Prunus avium) orchard near East Lansing, Michigan, for experiments on apothecial development and ascospore discharge, respectively. Disks cut from the leaves were incubated at six temperatures in experiments on apothecial development (4-24 C), and on ascospore discharge (8-30 C). Microscopic examination of crushed apothecia was used to evaluate changes in maturity. The number of asci per apothecium and the percentage of mature plus discharged asci after 7 days of incubation were related to temperature with quadratic regression analyses. The predicted optimum temperature for development of asci was 13.3 C, and the predicted optimum for apothecial development was 16.6 C. Temperatures of 4 and 24 C were unfavorable for apothecial development. The percentage of ascospores discharged from apothecia increased with increasing temperature over a range of 8-30 C.