Resistance analysis of 31 major rice blast resistance genes against Magnaporthe grisea(Hebert) Barr population in Guangxi

【Objective】 The objective of the study was to identify and evaluate the resistance of 31 known major rice blast resistance genes to Magnaporthe grisea(Hebert) Barr in Guangxi,to make clear their application value in rice breeding in Guangxi,and to provide theoretical support for the selection and breeding of new rice blast resistance varieties, the effective polymerization of resistance genes,and the rational layout of blast resistant varieties.【Method】 Twentyfive blast resistant monogenic lines,six near-isogenic lines for resistance to rice blast,and three Guangxi local resistance source varieties of Gui R106,Hongjiaozhan and Zhaitang,and disease-susceptible varieties of CO39,and Lijiang Xintuanheigu,were used as the rice materials for the test. The indoor artificial spray inoculation was used to evaluate the resistance of 31 major rice blast resistance monogenic genes provided for the test using 328 Magnaporthe grisea monosporous strains from different ecological rice-growing region in Guangxi from 2018 to 2021. Field resistance identification was also carried out by natural nursery in blast zone. The resistance of the tested lines was evaluated. The joint resistance frequencies of any two rice blast resistance genes was analyzed. Cluster analysis of compatibility between rice blast resistance genes to the tested strains was conducted.【Result】 The resistance frequencies of the 31 major rice blast resistance genes to the monosporous strains of tested pathogens ranged from 0 to 84.5%. Most of the genes showed low resistance frequencies and high susceptibility in the blast zone nursery. The rice blast resistance genes with higher resistance frequencies were Pi-k,Pi-km,Pi-9,Pi-1 and Pi-z⁵,with the values of 84.5%,82.9%,80.5%,77.4% and 68.9% respectively,and these rice blast resistance genes showed better field resistance in the blast zone nursery. The analysis of the joint resistance frequencies of any two rice blast resistance genes revealed that the joint resistance frequencies of different combinations of rice blast resistance genes were higher than those of individual resistance genes to varying degrees,with Pi-km×Pi-9 combination having the highest joint resistance frequency of 97.9%. According to the cluster analysis of compatibility results between rice blast resistance genes and the tested strains,the 31 rice blast resistance genes for testing could be classified into two major groups. Group I included 24 weak rice blast resistance genes such as Pi-a(1) with resistance frequencies ranging from 0 to 57.0%,and group II included 7 strong rice blast resistance genes such as Pi-9 with resistance frequencies ranging from 41.5% to 84.5%.【Conclusion】 Rice blast resistance genes Pi-k、Pi-km、Pi-9、Pi-1 and Pi-z⁵ have high resistance frequency to M. grisea in Guangxi and show good field resistance in the blast nursery. Therefore,these genes can still be used for future rice breeding according to local conditions in Guangxi. Gene polymerization is expected to select and breed rice blast resistance varieties with broader resistance spectrum.