Genetic analysis of microsatellites associated with resistance against bacterial leaf blight and blast diseases of rice (Oryza sativaL.)

Bacterial leaf blight (BLB) and blast are among the most destructive diseases of rice. In order to develop new varieties that can resist various races of the pathogensXanthomonas oryzaepv. oryzae(Xoo) andMagnaporthe oryzae, which cause these two diseases, respectively, it is important to identify suitable markers and a marker-aided selection strategy. Seventeen foreground microsatellites associated with resistance against BLB and blast were screened for polymorphism for possible adoption in a breeding program for resistant cultivar development. A total of 472 background simple sequence repeats (SSRs) were also screened for polymorphism in order to recover the recurrent parent genome. All 72 F(1)progenies were also analysed with the 17 foreground and 472 background markers in comparison to the alleles of their parents. The markers were validated using 218 BC(2)F(2)plants. The result revealed six tightly linked polymorphic foreground markers (Xa21FR, pTA248, Xa13prom, MP, RM21 and RM13) associated with resistance againstXoopathotype P7.7 and two microsatellites (RM6836 and RM8225) associated with resistance against blast pathotype P7.2. A total of 79 polymorphic background markers were identified for recovering the recurrent parent genome. The result also showed that the markers had goodness of fit (blast resistance) to 1:2:1 ratio for single gene model in BC(2)F(2)progenies. These genetically confirmed microsatellite markers were recommended for use in marker-assisted backcross breeding and other marker-assisted selection of BLB and blast resistance genes in order to develop varieties with durable and broad spectrum resistance against the two major rice diseases.