Genetic Diversity Of Magnaporthe Oryzae Populations From Nine Blast Nurseries In Southern China

Rice blast caused by the filamentous fungus Magnaporthe oryzae is the most devastating disease of rice,and its occurrence and epidemic seriously restrict the safe production of rice.Breeding and planting disease-resistant varieties is one of the most cost-effective ways to control this disease.However,after 3-5 years of large-scale promotion of rice varieties,their resistance usually decreases or even completely loses which is closely related to the complex genetic structure and frequent variation of Magnaporthe oryzae.Therefore,monitoring the genetic diversity,structural variation and dynamic changes of the Magnaporthe oryzae population is of great significance for revealing the epidemic and evolution of the disease,the selection and breeding of disease-resistant varieties,the rational layout and rotation of disease-resistant varieties,the extension of the service life of disease-resistant varieties and the effective prevention and control of this disease.Therefore,in this study,genome-wide SNP markers of rice Magnaporthe oryzae based on KASP（Kompetitive allele specific PCR）technology and SNP marker for mating gene MAT1 detection were developed to analyze the genetic diversity,structure and mating type of Magnaporthe oryzae population from nine blast nurseries in southern China.Genetic diversity and structure analysis were carried out for the Magnaporthe oryzae isolated from one of the disease nursery,leaf blast and panicle neck blast.Analysis of pathogenic type of rice blast strains in Hunan Province.The main research results are as follows:（1）A total of 2,397 single spores were isolated from rice blast samples collected from nine nurseries.A total of 157,024 SNPs were detected by genome-wide resequencing of mixed samples of single spores isolated from panicle neck blast.After screening and testing,142 SNPs distributed on the seven chromosomes of Magnaporthe oryzae were selected to develop KASP markers,and 444 panicle neck blast strains isolated from nine blast nurseries were genotyped.The results showed that the above strains could be divided into 3 groups,the dominant group was group I,and the number of strains was 218,accounting for 49.10%;The number of group II strains was 83,accounting for 18.69%,and the number of group III strains was 143,accounting for 32.21%.All of the Fujian,Guangdong and Guangxi strains belong to group I;The other strains were composed of two groups,strains from Zhejiang and Jiangxi belong to groups I and III,and strains from Yangliu,Taojiang,Xiangxi in Hunan and Sichuan belong to groups I and II.（2）The genetic structure analysis of the isolated seedling leaf blast and panicle neck blast strain populations collected and isolated in the same rice growing season in Liuyang blast nursery in Hunan Province showed that PCA and Structure analysis could not separate the population of seedling leaf blast and panicle neck blast strains,and the degree of genetic differentiation between them was low,and the differentiation coefficient F_st between the populations was only 0.05.The values of genetic diversity among individuals within the population were similar,with the average nucleotide diversity Pi value of 0.473 for seedling leaf blast strains and 0.478 for spike neck blast strains.These results showed that the genetic differences of rice blast strains infected with different tissues of rice at different times of the same rice growing season were small,and the variation mainly came from between individuals.（3）Through the published genomic data of rice Magnaporthe oryzae,the KASP marker for detecting mating gene MAT1 was developed,and from 9 blast nurseries 444strains were detected,and the results showed that 216 strains were MAT1-1,accounting for 48.64%;217 strains were MAT1-2,accounting for 48.87%;There were also 11single spores tested were MAT1-1/MAT1-2,accounting for 2.49%.Among the three genetic groups,the distribution of mating types was different.Among Group I the proportion of genotype MAT1-2 strains was 98.98%,and the proportion of MAT1-1/MAT1-2 strains was 1.01%.Among Group II,MAT1-1 strains accounted for 95.62%,MAT1-2 strains accounted for 0.73%,and MAT1-1/MAT1-2 strains accounted for3.65%.Among the group III,MAT1-1 strains accounted for 88.58%,and MAT1-2 and MAT1-1/MAT1-2 strains each accounted for 5.71%.These results suggest a significant association between mating pattern and group division.（4）Tweenty monogenic lines were inoculated with 29 Magnaporthe oryzae strains from Hunan Province.The results showed that the control Lijiang Xintuan Heigu susceptibility to all strains,and the resistance frequency of monogenic lines were between 0.00%and 96.55%,among which the resistance frequency of Pi-a,Pi-k^s,Pi-b,Pi-11,Pi-19 and Pi-20 was lower than 10%,and the resistance of Pi-19 and Pi-20was completely lost.The resistance frequencies of Pi-zt,Pi-1,Pi-5,Pi-7 and Pi-9 were higher than 90%,and these genes could be used in rice blast resistance breeding in Hunan Province.