Abstract：：Potato（Solanum tuberosum L.）early blight pathogen in Wuxi County，Chongqing city was isolated and identified，and its biological characteristics were studied．The results indicated that there were septate and branch hyphae in mycelium of potato early blight pathogen in Chongqing area．And the conidiophore was solitary or clustered，and the spore was of clavate or grenade shape．The size of conidia was（46.32-156.33）μm×（11.58-28.95）μm with longitudinal and latitudinal septa．Analysis of rDNA-ITS sequence of pathogen indicated that the strains were Alternaria sonali Sorauer．Studies on its morphologic characteristics indicated that light had no remarkable influence on mycelial growth，but darkness was favorable for spore-bearing．The optimum temperature for mycelial growth ranged from 27 to 28 ℃，the optimum pH value was 6．The optimum temperature for conidial germination was 30 ℃，the optimum pH value was 7-8．Studies on nutritional characteristics showed that sucrose，fructose，lactose，maltose and starch were more favorable for mycelia growth than dextrose，among which sucrose，fructose，lactose were better than carbon sources，and glycine and nitrate nitrogen could promote mycelia growth，but ammonium nitrogen could inhibit mycelia growth．
