Abstract:  Pyricularia fungi could infect not only rice， but also many other gramineous and cyperaceous plants. Many reports indicated that Pyricularia strains from grass around paddy field had relationships with the occurrence of rice blast， and avirulence （AVR） gene played an important role in rice\|blast interaction. AVR genes were often variable and could be used to study the diversity of genetic structure of Pyricularia strains.The present study constructed neighbor\|joining （NJ） trees to analyze 35 Pyricularia strains isolated from grass hosts. The results showed that the isolates were divided into two groups， isolates from Digitaria sanguinalis was a distinct phylogenetic group， and the other isolates from Eleusine indica and Setaria viridis were another phylogenetic group. Meanwhile， 27 pairs of primers were selected to amplify AVR genes from these isolates. The results indicated that the mutation types of AVR genes in these isolates included complete deletions， insertion， partial deletions and multiple fragments， and the main mutation type was complete deletion. We also carried out the statistics to analyze the amplification rate of AVR genes， which implied that none of these isolates contains all AVR genes， and AVR\|Pik/km/kp， PWL3 and PWL4 cannot be amplified in all strains. Moreover， ACE1， AVRPiz\|t， AVR\|Pita1 and PWL1 were not contained in isolates from Digitaria sanguinalis， and there was no AVR\|Pia， AVR\|Pita1， AVR\|Pita2 and PWL2 amplification in isolates from Eleusine indica， and no AVR\|Pii， AVR\|Pia， PWL1 and PWL2 amplifications in isolates from Setaria viridis.

Key words: Pyricularia, grass hosts, AVR gene, mutation