A total of 148 samples of potato black scurf were collected from 15 potato producing counties in Inner Mongolia Autonomous Region of China, and the strains were identified to be Rhizoctonia solani. The collected R. solani strains were grouped into three types, fast growth, slow growth and medium growth, based on the mycelial growth rate. Most of the fungi isolated were of fast and medium growth types. To examine the anastomosis groups of isolated R. solani strains, the isolated strains were co-cultured with anastomosis standard strains on sterile slide glass, and the occurrence of mycelial fusion was observed under microscope. The examination results indicated that 45 strains(73.77%), four strains(6.56%), and three strains(4.92%) belonged to AG-3, AG-1-IB and AG-2 anastomosis groups, respectively, while nine strains(14.75%) did not belong to any anastomosis groups above. These results suggested that the dominant strains causing potato black scurf in Inner Mongolia Autonomous Region were mainly R. solani AG-3. To test the pathogenicity of different anastomosis groups of R. solani, the potato tubers were planted with soil infected by isolated fungi. The results showed that all the tested fungi were able to cause typical symptoms of potato black scurf on tubers and stalk, but their pathogenicity levels varied. Moreover, it was found that the mycelial growth rate was positively correlated with their pathogenicity.
