Abstract:Thielaviopsis basicola (Berk.et Br.)Ferr. causing tobacco black root rot were isolated with modified carrot disks from 5 provinces of China, and their pathogenicity differentiation were studied by root cutting inoculation method. In the study, the disease resistances of 7 main tobacco cultivars against different T. basicola isolates were also evaluated. A total of 14 isolates of T. basicola were obtained, and their pathogenicity showed significant difference. The disease index of 14 isolates ranged from 29.2 to 62.5, in which 4 isolates showed high pathogenicity, 10 isolates were at moderate level, and no weak pathogenic isolate was found. The disease resistances were significantly different among the 7 cultivars when different cultivars were inoculated by a certain T. basicola isolates. The disease resistance changed from resistant, moderate resistant to susceptible and highly susceptible. The resistance of Guiyan 4, Qinyan 96 and Zhongyan 100 were higher than those of other tested cultivars.