Abstract：Studies on infectious condition and pathogenicity of Helminthosporium carposaprum have indicated that temperature and moisture keeping period can greatly affect the infection of Helminthosporium carposaprum. When the temperature was 10 ℃, the pathogen incubation period was 120 h. When the temperature was 25 - 30 ℃, the incubation period was only 74 h. The longer the moisture keeping period, the shorter the being infectious period. The shortest leaf moisture keeping period was about 6 h. The best combination of temperature and moisture keeping period for infection was 25 - 30 ℃ and 42 – 48 h. The susceptibilities of different tomato varieties to Helminthosporium carposaprum were significantly different. 704, 7929, 7913 were susceptible varieties, 08HN31, 7945, 08HN30 were resistant varieties. There existed differences in pathogenicities of different seedling ages. The pathogenicity of 10 days age was the strongest, while that of 5 days or 20 days ages were the weakest.
