| Rice is the most important food crop in Jiangsu province,among which japonica rice accounts for about 90%of the rice planting area.Rice blast is the most important fungal disease threatening rice production.Selecting suitable resistant genes to cultivate resistant varieties is the most economical and effective strategy to reduce the occurrence of disease.At present,more than 30 blast resistance genes have been successfully cloned.However,due to the wide and complex interactions among different genes and genetic backgrounds,the breeding values of different blast resistance genes are not consistent in breeding practice.Therefore,it is a key link to carry out rice blast resistance breeding efficiently by mining and screening excellent genes/gene combinations that contribute greatly to blast resistance in certain ecological regions.In this study,14 functional molecular markers of blast resistance genes were used to analyze the genotype information of 218 japonica rice varieties/lines developed and promoted in Jiangsu in recent years.The blast resistances of these varieties/lines were identified by blast strains from different regions in Jiangsu.Combined with genotype and phenotype,the genes/gene combinations with important value for blast resistance breeding of japonica rice in Jiangsu were screened.At the same time,24 rice blast resistance single gene lines were inoculated with some of the collected strains to evaluate the resistance effect of each gene.The main results are as follows:1)In 218 japonica rice varieties/lines,only 2 were detected carrying Pigm.The frequencies of Pi25(2.75%)、Pit(4.13%)and Pil(5.86%)were relatively low.The frequency of most genes were between 10%and 30%,Pita and Pikh were about 50%,and the highest frequency gene was Pib(79.82%).In terms of varieties,the number of genes carried by most varieties was between 2 and 5,18 varieties carry only one gene,and 7 varieties carry more than 7 genes.The results suggested that there were significant differences in the known blast resistance genes carried by Jiangsu varieties,and Pikh,Pita and Pib were widely used in general.2)Total of 218 tested varieties/lines were inoculated with 5 groups of mixed blast strains respectively.At the later stage,two evaluation methods of rice neck blasts were used to determine the disease grade of each variety.Statistical analysis showed that the resistance level of tested varieties to neck blast was generally poor,the proportion of susceptible varieties was more than 50%,and the proportion of resistant to moderate resistance varieties was relatively small.In the multigene logistic regression analysis of 10 disease grade data of 5 groups of different mixed strains,Pita was detected to have significant contribution to blast resistance in all 10 times analysis,followed by Pi3/5/i(9 times),Pit(6 times),Pia(6 times),the rest were detected less than 3 times,and there were 4 genes not detected to have significant contribution.Through comparing the disease grades of the varieties carrying different genes/gene combinations with significant contribution,we found that the resistance effects of Pita,Pi3/5/i and Pia alone were not obvious,while the resistance effect of Pit alone was better.In terms of gene combinations,Pita almost participated in all the combinations with significant contribution to resistance effect,and the resistance effect of Pita+Pia combination was the best,followed by Pita+Pi3/5/i,and finally Pia+Pit.The results showed that there might be extensive genetic interactions among some resistance genes,which would eventually affect the resistance effects of blast genes.3)The seedling blast resistance of 118 varieties/lines was identified by inoculating 33 single spore strains,and 63.6%of the varieties had resistance spectrum of 80%or more.There were only 6 varieties with resistance spectra less than 60%,accounting for only 5.1%of the tested varieties,and 38 varieties/lines with more than 90%resistance spectra,accounting for 32.2%.These results suggested that the resistance of these varieties to blast was better.Multigene logistic regression analysis showed that the contributions of Pi3/5/i,Pita and Pit genes to seedling blast resistance reached significant or extremely significant levels,and the average resistance spectrum of the varieties with single gene was slightly higher than that of the control,but there was no significant difference.Through comparing the resistance spectra of different genes/gene combinations,it was found that the Pi3/5/i+Pita gene combination had the broadest resistance spectrum(94.7%).4)24 blast—resistant single—gene lines under the background of Lijiangxintuanheigu(LTH)were inoculated by 59 single—spore strains.The results showed that LTH was susceptible to all inoculated strains.The resistance spectra of Pi5(72.9%),Piz5(72.9%)and Pi9(76.3%)single—gene lines were relatively high.In addition,the resistance spectra of 11 single—gene lines were concentrated between 40%and 60%,and the rest were lower.According to the combined resistance coefficient(RAC)and combined pathogenicity coefficient(PAC)of each single—gene line to the tested strains,it is suggested that the gene combinations of Piz5+Pi9(RAC=0.59,PAC=0.10)and Pi5+Pi9(RAC=0.56,PAC=0.07)may be of high application value in rice blast resistance improvement in Jiangsu Province.The above results provide references for selecting appropriate resistance genes or gene combinations in rice blast resistance breeding in Jiangsu province,and have important practical significance. |
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