Mycosphaerella chaenomelis sp. nov.: the teleomorph of Cercosporella sp., the causal fungus of frosty mildew in Chaenomeles sinensis, and its role as the primary infection source

A leaf spot disease called frosty mildew was observed on Chaenomeles sinensis throughout Japan. Small brown spots with white tufts occurred followed by successive defoliation. On the fallen leaves, minute black dots are formed. The causal fungus was regarded as a new species of Mycosphaerella, M. chaenomelis, and Cercosporella chaenomelis in anamorph. Pathogenicity of the fungus was confirmed only in C, sinensis by inoculation experiments. Colonies of the fungus grew well on potato sucrose agar, and grew at 10–30°C with an optimum temperature of 25°C The fungus overwintered on the fallen diseased leaves in the form of pseudothecia, and ascospores served as the primary infection source from April to June.