Abstract: 【Objective】Leaf brown spot is a main disease causing defoliation of apple tree in early season. Information about sporulation condition and dynamic of the fungus on overwintered leaves is prerequisite for determining primary infection season and primary inoculum quantity, which are helpful for effectivecontrol of the disease. 【Method】Effects of temperature and moisture on sporulation of Diplocarpon mali on overwintered apple leaves were tested under controlled environments in 2009 and 2010.【Result】Results showed that the overwintered fungus produced pseudoconidia at temperature ranging from 0 to 30℃ with an optimum at 15.5℃. Being wetted or in high relative humidity environment was necessary for overwintered fungus to produce pseudoconidia. After being wetted or putting into environment with relative humidity over 97%, the fungus formed abundant pseudoconidia within 6 h. When incubated at 15 or 20℃ for more than 36 h, the overwintered fungus in wetted leaves, sampled in early March, produced few apothecium. The observed frequency of apothecium in the inspected stromas was 0.34%. However, the frequency rose to 5.4% on overwintered leaves sampled in late May, and 27% overwintered leaves borne apothecium.【Conclusion】 In spring, when the average diurnal temperature rises to or above 5℃, 5 mm rainfall would wet the overwintered leaves and stimulate the fungus to produce abundant pseudoconidia within 6 h. When the average diurnal temperature rises to 15℃, 24 hours’ rainfall would stimulate the formation of apothecium and ascospores. The two kinds of spores are pathogenic to apple leaves and provide abundant inocula for the disease primary infection.

Key words: Diplocarpon mali , overwintered pathogen , sporulation , conidium , ascospore