Analysis Of Genetic Diversity Among Populations And The Preliminary Forecasting Of The Virulence Gene Distribution Frequency For The Rice Blast Fungus Magnaporthe Oryzae In Southwest Region Of China

Rice blast caused by rice blast fungus (Magnaporthe grisea) is one of the three major diseases of rice production in the World. In Southwest, this disease is one of the main diseases in the single-season rice, and it showes a extremely high incidence rate in middle-west Sichuan basin, South GuiZhou and SW Yunnan and other areas. Therefore, devote to the stduy of population genetic structure and diversity and the virulence gene for Magnaporthe oryzae are of great significance for variety breeding, rational distribution and prolonging the lifetime of resistant variety.In this study, many single spore isolates of magnaporthe grisea from eight counties (city) in Southwest region were isolated.The genomic DNA of those isolates were designed by 13 pairs of SSR primers and 16 pairs of virulence gene specific primers with PCR amplification.The 0-1 database based on the Sequence of SSR and virulence gene was built according to the effect. Population genetic structure and diversity of Magnaporthe oryzae was analyzed by series of software.The distribution frequency of the virulence gene was forecasted preliminary according to the amplification results. Conclusion follows:1. Two hundred single spore isolates of magnaporthe grisea were isolated. Among them,52 from Ya’an,37 from Wenjiang,33 from Nanchong,6 from Zigong,25 from Yongchuan,24 from Dianjiang,15 from Liangping,8 from Meitan.2. The specific bands can be amplified by the specific primers of 13 pairs of SSR primers, and its amplification frequency over 95.00%, which showed the high frequency amplification. The target bands can be amplified by the specific primers of 16 pairs of virulence gene, and the amplified frequencies were quite different.3. Population genetic structure of magnaporthe grisea from southwest region was complicated and showed abundant hierarchies. Two hundred isolates were classified into 90 different haplotypes, which included 1 absolute advantage haplotype,22 secondary haplotypes and 67 infrequent haplotypes. Those isolates were classified into 24 genetic lineages at 0.90 similar levels, which included 1 absolute advantage lineage,5 subdominant lineages,7 secondary lineages and 11 minor lineages. Haplotypes and genetic lineages of magnaporthe grisea from 8 regions were very rich. The isolates from the same source can be attributed to the different haplotypes and genetic lineages. The same haplotype or genetic lineage were not showed the same source all. It was reflected a certain degree of specificity and significant diversity in each area at the population genetic structure,4. Genetic diversity of magnaporthe grisea from southwest region was very abundance through the analysis of genetic parameters. In the population genetic level: Effective number of alleles (Ne) was 1.4466; Nei’s gene diversity index (H) was 0.2753; Shannon’s Information index (I) was 0.4291; Number of polymorphic loci (NP) was 28; Percentage of polymorphic loci (P) was 96.50%. Genetic level of each population showed some difference in different regions. Population from Nanchong showed the higher genetic diversity. The followed higher relatively were Zigong, Yongchuan, Yalan. The lower relatively were Wenjiang and Dianjiang. Liangping and Meitan showed the lowest genetic diversity.5. Population from southwest region showed some genetic variation. Diversity inter groups (59.86% of the total genetic variation) was greater than the interal groups (40.14% of the total genetic variation) (Gst=0.4014).6. The ranges of Nei(1972) not bias genetic distance and genetic similarity were 0.0357～0.6173 and 0.5394～0.9649, respectively. The average genetic distance and genetic similarity of 8 inter groups were 0.1901 and 0.8383, respectively. Genetic relationship of magnaporthe grisea population from near to far were Ya’an, Nanchong, Dianjiang, Liangping, Meitan, Wenjiang, Yongchuan and Zigong.7. Amplification frequency of inter groups and interal groups by the specific primers of pathogenicity gene and most avirulenc gene showed large difference, which could forecast the distribution frequency of the virulence gene preliminary and provide some references for pyramiding breeding, variety distribution and prolonging the lifetime of resistant variety.