Genetics of resistance in rice cultivar, IR20 and Semora Mangga to Philippine and Japanese races of bacterial blight pathogen

Abstract

To develop near-isogenic lines with monogenic resistance to bacterial blight (BB) in rice, a rice differential cultivar, IR20, was analyzed using Japanese and Philippine BB races. Another rice cultivar, Somora Mangga, identified to be carrying Xa-4^b (an allele of Xa-4) was also studied using Philippine races . Analysis of F₂ and F₃ populations (from the cross IR24/IR20) using Japanese and Philippine races revealed that IR20 has Xa-1 and Xa-12 in addition to Xa-4 which was considered to convey resistance to Japanese race IIIA. The allelism test between IR20 and Java 14 showed that Xa-3 and Xa-4 are very closely linked. The allele test between Semora Mangga and Java 14 showed that Semora Mangga has Xa-3, not Xa-4^b as reported earlier. Thus, gene symbols Xa-4^a and Xa-4^b are redundant. The results show that Xa-4 conveys resistance to Japanese races IA, II, IIIA, and V as well as to Philippine race 1 and moderate resistance to race 4.