Genome-wide Association Study Of Rice Blast Resistance And Blast Resistance Improvement Of Two Japonica Varieties

Rice blast is one of the critical factors that reduce rice production. To select blast resistance materials and search for resistant loci by genome-wide association study( GWAS) from 1219 germplasms, the accessions were plant in serious infected area for natural induced blast in different stages and the incidence of blast were investigated. On the other hand, donors of blast resistance genes Pi9, Pigm and pi21 were used to improve blast resistance for Jingzuo1, and blast resistance genes Pigm, Pi33, Pi1 as well as fragrance gene fgr were used to improve blast resistance and fragrance for Ninggeng43. Main results were as follows:1. The 1219 accessions with similar growth duration were planted in Enshi for natural induced blast and resistance evaluation. A total of 34 accessions with good field performance and strong blast resistance were selected from the 1219 accessions. Among these resistant materials, 17 accessions were confirmed to be with broad-spectrum blast resistance through inoculating 30 indica isolates at seedling stage, which can be used as resistance resources. And among the 17 accessions, EJ0537, EJ0616 and EJ0666 are also with good agronomic traits, thus showing great potential application.2. GWAS were conducted with threshold P < 108 using 6,350,347 SNPs and phenotypic data of blast incidence in different stages and different nurseries. Only a few of loci associated with seedling blast and leaf blast were detected, while the amount of loci associated with neck blast was big. For instance, there were 1345 loci associated with neck blast rate of indica in Bajiao nursery. Searching the flanking regions of associated SNPs, 69 rice blast resistance genes that were reported, 36 regulation genes in blast response and some new R genes were found. However, the exist of these associated loci should be further examined.3. Different resistance-improved lines with genetic background of Jingzuo1 were obtained by marker-assisted selection( MAS). And inoculation of 15 indica isolates and 15 japanica isolates were conducted to indentify the blast resistance of improved lines at seedling stage. The resistance frequency of the resistance-improved line with Pi9 reached 100%, and that of the resistance-improved lines with Pigm averagely reached 90%. Both of them were extremely significantly higher than that of recurrent parent Jingzuo1. And the agronomic traits of these lines were quite similar with that of Jingzuo1. The resistance-improved line with pi21 had no significant difference of resistance frequency with Jingzuo1, but had significantly decreased grain yield per plant as compared with Jingzuo1. Comparing with Jingzuo1, the resistance frequency of pyramiding line of Pi9 + pi21 was significantly improved, reaching 93.33%, with significant decrease in grain yield per plant. The results indicated that Pi9 and Pigm show great potential application in rice breeding for blast resistance, while the use of pi21 should be thoroughly considered.4. Different resistance-improved lines with genetic background of Ninggeng43 were obtained by MAS. And Inoculation of 15 indica isolates and 15 japanica isolates were conducted to indentify the blast resistance of improved lines at seedling stage. The resistance frequency of the resistance-improved line with Pigm reached 80%, and that of the resistance-improved line with Pi33 reached 60%. Both of them were extremely significantly higher than that of recurrent parent Ninggeng43. The resistance frequency of pyramiding line of Pigm + Pi33 reached 76.7%, which was between that of resistance-improved line with Pigm and resistance-improved line with Pi33. The results indicated that the blast resistance spectrum of Pigm is broader than that of Pi33, and there may be negative effects when pyramiding the two genes. The effect of fragrance gene fgr and pyramiding it with blast resistance genes should be further examined.5. The resistance frequency of Pigm with genetic background of Jingzuo1 and Ninggeng43 both increased by 40%, suggesting that the expression of Pigm may not be influenced by genetic background. Therefore, it can be widely used in rice breeding for blast resistance.