Abstract：Alternaria is an important plant pathogen with a variety of species．It often brings serious losses to crop production．In 2019，a cucumber disease suspected to be infected by Alternaria was found in Qiqihar cucumber greenhouses in Heilongjiang Province．After isolated culture，purification and pathogenicity determination，pathogen identification was carried out on the collected susceptible samples by morphological observation and molecular biological analysis．The results showed that the pathogen of cucumber leaf spot found in Heilongjiang Province was Alternaria alternata．Studies on its biological characteristics indicated that the fastest culture medium of mycelia was CA，cucumber juice culture medium．The optimal carbon source was glucose and sucrose，and nitrogen source was peptone．The optimal culture conditions were 28 ℃ and pH 8-9．The lethal temperature was 55 ℃ for 10 min．The influence of light on mycelia growth was not significant．PDA and CA culture medium were the most suitable culture medium for pathogen spore production．The most suitable carbon and nitrogen sources were glucose and peptone, respectively．The spore production was maximum at 28 ℃，pH 8-9，12 h light on and 12 h darkness．
