Influence of temperature and moisture on germination of ascospores and conidia of Botryosphaeria obtusa

Maximum germination of conidia of Botryosphaeria obtusa occurred in free water and declined as relative humidity (RH) was reduced from 100 to 92%; no germination was observed at 88.5% RH. Germination in free water reached 80% in 4 hr at 16-32 C and in 12 hr at 12 C but was only 23 and 0% at 8 and 4 C, respectively, after 12 hr. Higher temperatures were required for germination at 95 and 92% RH (16 and 28 C, respectively) than at 98, 99, and 100% RH (12 C). Conidial germination at 92% RH was observed only after 12 hr at 28 C. The two isolates tested differed in temperature and relative humidity requirements for germination. Requirements for ascospore germination were similar to those for conidia. Germ tube lengths of ascospores and conidia were maximum in free water and decreased with decreasing relative humidity. After 12 hr in free water, ascospore germ tubes reached a maximum mean length of 0.78 mm at 28 C, whereas maximum conidial germ tube length was 0.82 mm at 24 C for isolate 087 and 0.99 mm at 28 C for isolate 049. Germ tube length of both types of spores declined at 32 C