Abstract：17 samples of Alternaria spp. which is the pathogen of wheat black point were collected from five different places in Henan, and their genomic DNAs were extracted by CTAB. The ribosomal DNA internal transcribed spacer (ITS) region of the genomic DNAs was amplified and sequenced, the homology of the 17 isolates was 99%-100%. The sequences were analyzed by phylogenesis with 9 species of Alternaria spp. from GenBank. The result showed that all the isolates had high homology The homology of the 6 small-spored species A. alternata、A. tenuissima、A. mali、A. gaisen、A. citri、A. arborescens is 98%-100%, and the other three large-spored species A. radicina、A. porri and A. solani were separated clearly. There are also some certain relative relationship between the mutation isolates of small-spored species and the large-spored ones. The rDNA ITS1-5.8S-ITS2 of all the isolates did not have the regionally and host characters but had high conservation with special sequences respectively, which can be the important evidence in the classification, identification, molecular marker and phylogenetic analyses of some certain species of epiphyte. The result also prove by molecular evidence that some similar small-spored species of Alternaria spp. are the pathogens of wheat black point in Henan.
