Abstract: 【Objective】The objective of this study is to identify avirulence genes (Avr-genes), which existed in the prevalent fungus of Magnaporthe oryzae, understand the distribution of Avr-genes in the epidemic strains of different regions, and to provide references for rice cultivars distribution.【Method】According to the sequences of 6 Avr-genes which had been cloned and were associated with the rice blast pathogenicity, the primers were designed to amplify the target sequences of the epidemic rice blast fungus in Liaoning Province. The DNA, extracted from the 26 strains of rice blast fungi, was used as a template for PCR amplification. By analyzing the PCR products by AGE (agarose gel electrophoresis) and sequencing, the sequences of base and amino acid for each Avr-gene were examined and compared. Some candidate primers were designed to check out the Avr-gene which had no PCR product.【Result】There was no PCR product when amplified Avr1-CO39, Avr-pia and Avr-pii by the primers, and there was also no PCR product by using the candidate primers, which showed that Avr1-CO39, Avr-pia and Avr-pii didn’t exist in most of the M. oryzae isolated from the main rice growing regions in Liaoning Province. On the contrary, the PCR products of AvrPiz-t, Avr-pik and Avr-pita were detected by AGE, and different genome types showed the 3 genes below were carried by the fungus in different mutated types and rates. AvrPiz-t related to the resistant genes including Pi2, Pi9 and Piz-t was detected in 22 M. oryzae strains, and the sequences of 21 strains were same to which exited in AvrPiz-t. The results of this experiment illustrated that the rice varieties carrying Pi2, Pi9 or Piz-t could have broad-spectrum disease resistance to rice blast fungi. The sequence of No. 16 strain was not the same as others, because it lost a single base C in the position of 192 bp, which caused the frame-shift mutation. The mutation led the AA (amino acid) sequence to terminate in position of 72nd AA, and made the secretory protein lose the function of avirulence. Avr-pik associated to the resistant genes like Pik, Pik-p, Pik-m and Pik-s were detected by AGE. The results showed that all the strains had the target bands. Their sequence showed that there were 4 genotypes of Avr-pik allele in the strains (B, D, F and G), and genotype D which carried by 12 strains could be recognized by rice blast disease resistance genes of Pik and its alleles as Pik-m and Pik-p. The 9 strains which carried genotype B of Avr-pik had been reported before, but its function of virulence had not been tested. The genotype F which exited in two strains was firstly found to be the new allele of Avr-pik, and they appeared in Dandong and Panjin, respectively. The specific point mutation, the 143 (A/G) of the base sequence, was the difference between genotype F and D. Genotype G which was also firstly detected was carried by the remaining 3 strains which only appeared in the area of Xinbin County in Fushun. The difference between genotype G and D was the point mutation of 168 (G/A) in the base sequence, which caused the protein translation early termination, therefore, genotype G lost its avirulent function. According to the AGE results, the same bands of Avr-pita were detected in all the 26 strains, and the sequences were tested and analyzed. The results showed that the genes in 26 strains had 5 genotypes of alleles, and there were several point mutations between the 5 alleles and the Avr-pita sequence, and the changes of the sequences caused the missense mutation. The difference of AA among the 5 genotypes were the 3 point mutation of 83 (D/N), 192 (Y/C) and 207 (K/R), which had been found in a structural domain of Avr-pita. The genotypes of allele all had been reported before. 【Conclusion】 The M. oryzae who carried Avr-pik, Avr-pita and AvrPiz-t distributed widely in rice growing regions of Liaoning Province. Breeding and cultivating the rice varieties carrying the corresponding resistance genes could alleviate the damage of the rice blast.

Key words: Liaoning Province , Magnaporthe oryzae , avirulence gene