Highlights in Identification and Application of Resistance Genes to Bacterial Blight

The international differential system for resistance to bacterial blight(BB) was established using a common base of research methods by collaborative studies between Tropical Agricultural Research Center(TARC) and International Rice Research Institute(IRRI) in 1982-1987.Up to June 2005,there are a total of 30 BB resistance genes registered internationally or reported in international journals.Among them,the genes Xa22(t),Xa26(t),xa26(t),Xa27(t),Xa28(t),Xa29(t) and three Xa25(t) were tentatively designated and subjected to further be re-arranged.Twenty-one and 9 out of the 30 Xa genes are dominant and recessive,respectively.Thirteen genes exhibit all-growth-stage resistance,two genes Xa21 and Xa25(t)(O.minuta) express resistance at the later tillering stage,and the other 15 genes confer only adult-stage resistance.Seventeen Xa genes were mapped,including Xa3,Xa4,Xa10,Xa21,Xa22(t),Xa23,and Xa26 on chromosome 11; Xa1,Xa2,Xa12,and Xa14 on chromosome 4;xa5 and xa13 on chromosome 5;Xa7 and Xa27(t) on chromosome 6;Xa25(t) on chromosome 12;and Xa29(t) on chromosome 1.Five Xa genes were cloned,including Xa1,xa5,Xa21,Xa26 and Xa27.Application of resistance to bacterial blight was also discussed.