Identification Of Rice Germplasm Resistant To Bacterial Blight And Molecular Mapping Of A New Resistance Gene

Rice (Oryza. sativa) is one of the world’s most important food crops, raising more than half of theworld’s population and playing an important role in food production. However, the diseases make asubstantial reduction in its production. bacterial blight is one of the three major diseases in rice.Selection and utilization of cultivars carrying resistant genes are proved one of the most economical,effective and environment-friendly strategies for bacterial blight management.Bacterial blight resistant breeding is an important way to improve disease resistance in rice.Screening, identification and innovation of resistant germplasm are the basis and precondition ofbreeding. In this study, we screened and evaluated476cultivars from22countries and27provinces ofchina, and found a cultivar with wide resistance spectrum and good agronomic traits, then mapped it.The results obtained in this study are as follows:1. Screening of resistant germplasm: To screen resistant cultivars against rice bacterial blight, wecollected476cultivars from22countries and27provinces of China and evaluated forresistance to rice bacterial blight using a Chinese representative strain HB17(C2) andinternational race PXO99(P6)by artificial inoculation method. The results show that there are91cultivars resistant to race C2,149cultivars resistant to race P6,74cultivars resistant to bothof them and no cultivars was immune to bacterial blight. We also inoculated150cultivarsamong the476cultivars by C4, P1and T1, and inoculated some cultivars resistant to C2andP6by multiple strains. Lots of materials with wide resistance spectrum were screened in thisstudy, such as Xiangwanxian3, Yangdao2, Dangyu5and Yelicanghua.2. Genetic analysis and construction of mapping population: crossed the rice germplasmXiangwanxian3and other resistant materials with susceptible cultivars JG30andIR24,constructed F2mapping population and genetic analysis,results show that the resistancegene Xiangwanxian3and Yangdao2harbour was controlled by one dominated gene.3. Molecular mapping of a new gene Xa39(t): To map the gene Xa39(t), bulked segregantanalysis (BSA) was adopted to survey SSR and EST molecular markers. Eighteen molecularmarkers FJ9, FJ28, FJ30, FJ46, FJ50, RM1024, FJ25, FJ21, FJ70, FJ19, FJ94, FJ101, FJ79,FJ124, FJ112, FJ114, FJ90and FJ8were found to show polymorphism between R-pool andS-pool. By analyzing the F2populations, the gene Xa39(t) was mapped on the short arm of ricechromosome5. The genetic distance between Xa39(t) and FJ9, FJ28, FJ30, FJ46, FJ50,RM1024, FJ25, FJ21, FJ70, FJ19, FJ94, FJ101, FJ79, FJ124, FJ112, FJ114, FJ90, FJ8is5.4cM,3.9cM,3.9cM,2.9cM,2.9cM,2.9cM,1.9cM,1.4cM,0.4cM,0.4cM,0.4cM,0cM,0.5cM,0.5cM,2.9cM,2.9cM,2.9cM and3.4cM. FJ9, FJ28, FJ30, FJ46, FJ50, RM1024, FJ25, FJ21,FJ70, FJ19and FJ94are on one side of Xa39(t); FJ79, FJ124, FJ112, FJ114, FJ90and FJ8are on the other side of Xa39(t); FJ101is cosegregating with Xa39(t). The new bacterial blightresistance gene Xa39(t) was mapped within a length of0.9cM on the short arm of ricechromosome5, between the marker FJ79and FJ94.