Abstract:To clarify the pathogens of potato early blight and their sensitivity to different fungicides, 180 samples of potato early blight were collected from 5 counties of Hebei Province during 2009-2011, and then isolated and purified by conventional method. Through morphological characteristics, pathogenicity test along with sequence analysis of the internal transcribed spacer region of the ribosomal DNA (ITS), two kinds of fungi were identified (A, B), with a ratio of 4:6. The sensitivity of the pathogens to different fungicides was also determined by mycelial growth rate test. Through further pathogenicity test it was demonstrated that A and B were the pathogen causing potato early blight. The preliminary morphological identification showed that A and B were Alternaria solani and Alternaria alternata, respectively. ITS sequences of A and B were amplified with universal primers of ITS1/ITS4, and compared with the GenBank database using BLAST analysis. The results showed that the nucleotide homogeneity between A and A. solani, B and A. alternata was 98% and 100%, respectively. Highly significant differences existed in the sensitivity of two pathogens to four fungicides, fludioxonil, boscalid, pyraclostrobin and difenoconazole, and no difference in the sensitivity to iprodione. Therefore, it confirmed that the pathogens of potato early blight in Hebei were A.solani and A.alternate, and their sensitivity to the same fungicide was different.