Effects of temperature, moisture, and wetness duration on the production of conidia and ascospores of Glomerella cingulata on diseased apple leaves

Glomerella leaf spot (GLS) caused by Glomerella cingulata (Colletotrichum spp.) is a devastating disease of apple (Malus × domestica Borkh.) in China. We evaluated the effects of temperature, moisture, and wetness duration on the production of conidia and ascospores on diseased leaves. The temperature required for producing conidia and ascospores by G. cingulata on diseased leaves ranged from 20 to 30°C, with an optimum of approximately 28°C. The pathogen on diseased leaves produced conidia and ascospores only when the leaves were wet or at RH=100%. Conidia could not form until the diseased leaves maintained wetness for at least 24 hours, and a modified Weibull model could describe the relationships between the number of conidia formed per cm2 of diseased leaves and temperature and wetness duration. The production of ascospores on the leaves infected by GLS required 20, 14, and 16 days of leaf wetness at 20, 25 and 30°C, respectively. The sporulation ability of G. cingulata on GLS leaves could last more than eight weeks. The half-life of sporulation or survival of the pathogen was 2.3 weeks when the diseased leaves were hung outdoors under natural conditions. Collectively, the sporulation of G. cingulata was a vital process affecting the occurrence and epidemic of GLS, and these results will provide valuable guidance for developing a model to predict the disease epidemics and establish effective control strategies.