Pathogenicity Analysis and Molecular Characterization of Three Avr Genes in Magnaporthe oryzae Population from...

Rice fungal blast, one of the most devastating diseases caused by Magnaporthe oryzae, poses a severe threat to global rice production. For the breeding and deployment of rice varieties with blast resistance, it is critical to elucidate the frequencies and genetic variations in avirulence genes among M. oryzae populations. In this study, a total of 294 M. oryzae isolates were collected in 2022 from central Jilin Province, China. Pathogenicity assays on 24 monogenic rice lines revealed extensive virulence variations among the 294 isolates, with highly pathogenic strains being dominant and clear geographic differences in pathogenicity profiles. Resistance frequencies differed markedly among 24 monogenic lines, with Pi3, Pit, Pi7, Pikh, Pik, and Pia showing resistance rates over 50% and Pish exhibiting the lowest efficacy. Moreover, resistance profiles varied significantly across four sampling regions in central Jilin Province, with Pit being the most effective in Changchun and Jilin, Pi3 in Tonghua, and Pikm in Liaoyuan. In addition, the Avr genotypes of the isolates were postulated based on phenotypic data from the monogenic rice lines. Among the postulated Avr genotypes, the frequencies of Avr-Pi11 and Avr-Pish were the lowest at 29.25%. Furthermore, molecular characterization of three Avr genes (Avr-Pi9, Avr-Pita2, and Avr-Pizt) was performed by sequencing a subsample of 50 randomly selected isolates. Natural mutation sites were identified in Avr-Pita2 and Avr-Pizt, which were located within the coding sequence regions, leading to non-synonymous mutations and nonsense mutations that cause premature termination. Notably, no mutation was detected within the coding sequences of Avr-Pi9. Collectively, the findings provide a theoretical basis for breeding blast-resistant rice varieties that can be deployed in central Jilin Province, China.