| Rice is the most important food crop in Jiangsu,with japonica rice accounting for more than 85%of the total rice area in Jiangsu.Rice blast is the most threatening fungal disease,and the selection of suitable resistance genes to breed disease-resistant varieties is the most cost-effective strategy to mitigate the occurrence of the disease.More than 30 resistance genes have been successfully cloned across the world,however,the complex interactions that may exist between different genes and with the genetic background lead to inconsistent breeding values of different disease resistance genes in breeding practice.Screening and identification of superior genes/gene combinations that contribute to rice blast resistance is an important preliminary work for breeding disease-resistant varieties to control the damage of the disease.Previous studies in our laboratory,using natural varieties,found that the disease resistance genes Pita,Pia,and Pi3/5/i have an important role in blast resistance in Jiangsu japonica rice,but Pita has almost no effect when alone,while it significantly enhances resistance when pyramiding with Pia or Pi3/5/i.To further verify this finding,we first selected specific varieties carrying the said genes,then designed and constructed rice that carrying different gene and genes,and finally conducted inoculation identification of the relevant rices to determine the resistance effect of different genes.At the same time,we analyzed which genes have important contributions in blast resistance by using the rice variety resources of Changshu Institute of Agricultural Science as materials,and provided theoretical references for further targeted parental selection and breeding of rice blast resistant varieties.The main findings of the paper are as follows:1.218 japonica rice varieties validated and promoted in Jiangsu in recent years were tested and analyzed by 14 markers of known resistance genes,from which candidate parental varieties carrying one or more of Pia,Pita,Pi3/5/i and,as far as possible,no other resistance genes were screened;then 9 crossbreeding combinationss between some varieties and related combinations with the broad-spectrum resistance gene Pigm were successfully formulated.In addition,121 strains carrying different genotypes were selected by marker-assisted selection in the F3 to F4 generation.2.The results showed that the pathogenicity of colony 6 from the Institute of Plant Protection,Jiangsu Academy of Agricultural Sciences was significantly stronger than that of the five groups of mixed spores previously isolated and collected in our laboratory;for the different genotypes of the strains,no highly resistant strains with level 0 of disease were found,and most of the strains had level 5 of disease or higher;The disease level data of the late tasseled material were generally higher than those of the early tasseled material.3.Multiple comparisons confirmed that the three genotypic combinations of Pita+Pia+Pi3/5/i,Pia+Pi3/5/i and Pita+Pia were significantly more resistant than other combinations and their respective single-gene materials,but still significantly less resistant than Pigm.There was no significant difference between the resistance levels of Pia,Pita,Pi3/5/i or their different combinations and Pigm single genes added to Pigm,indicating that the resistance effect of Pigm genes was extremely pronounced and may have masked the resistance effect of other genes.C onsidering the superior resistance of Pigm,it was suggested that the related gene combinations of Pita,Pia and Pi3/5/i might be more beneficial for breeding more durable and broad-spectrum resistant varieties in Jiangsu japonica rice for resistance to rice blast.4.The genotypes of 66 japonica rice varieties validated and promoted in Jiangsu in recent years were detected and analyzed in 14 known disease resistance loci,and no varieties were found to carry Pit genes,and the percentages of Pigm,Pi25 and Pil genes were also generally low;the genes with higher percentages were similar to those of previously validated and/or promoted japonica rice varieties,mainly Pib and Pita.Most varieties carried one to three known disease resistance genes Most of the varieties carried one to three known resistance genes,and half of them carried three genes,but there was no correlation between the number of genes carried and resistance.5.The genotypic analysis of 1242 varieties including conventional japonica parents,sterile lines,heterojaponica varieties/combinations and restorer parents preserved in the Changshu Agricultural Science and Technology Rice Laboratory using 14 functional markers of disease resistance genes revealed that the number of disease resistance genes carried by different types of varieties/lines differed significantly,among which the overall number of disease resistance genes carried by restorer lines and heterojaponica combinations was significantly higher than that of sterile lines and conventional varieties.For example,Pia had a higher proportion in the restorer parents and hybrid japonica varieties,but a significantly lower proportion in the conventional japonica parents,while Pit was lower in all material types.6.The results of inoculation identification of speckle blight showed that the average disease level of both the restoration and hybrid japonica lines was significantly lower than that of the conventional parental varieties and sterile lines,and the sterile lines had the highest disease level data with an average of 3.07,all of which were susceptible or highly susceptible types.By logistic regression with disease resistance genes,it was found that Pigm,Pita,Pid3 and Pi3/5/i contributed significantly to blast resistance in conventional parental varieties,Pi3/5/i and Pik contributed significantly to blast resistance in recovery lines,Pit and Pid3 contributed significantly to blast resistance in heterojaponica combinations,while no significant contribution was detected in sterile lines The results showed that Pigm and Pid3 contributed significantly to blast resistance in the heterojaponica combinations,while no significant contribution was detected in the sterile lines.Taken together,the results suggest that the genes Pigm,Pita,Pia,Pit,Pid3 and Pi3/5/i have important applications in breeding for rice blast resistance,especially blast resistance,in rice in Jiangsu,and it is necessary to enhance the breeding applications of the related genes in the future.The results will not only provide a theoretical basis for breeding for rice blast resistance,but also provide a reference for establishing a scientific and reasonable integrated rice blast prevention and control system,which is of great significance. |
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