Marker assisted selection of bacterial blight resistance genes in rice

Bacterial leaf blight caused by Xanthomonas oryzae pv. oryzae is one of the most important diseases affecting rice production in Asia. We were interes ted in surveying rice genotypes that are popularly used in the Indian breed ing program for conferring resistance to bacterial blight, using 11 STMS an d 6 STS markers. The basis of selection of these DNA markers was their clos e linkage to xa5, xa13, and Xa21 genes and their positions on the rice gene tic map relative to bacterial blight resistance genes. Eight lines were fou nd to contain the xa5 gene while two lines contained Xa21 gene and none of the lines contained the xa13 gene with the exception of its near-isogenic l ine. Using the polymorphic markers obtained in the initial survey, marker-a ssisted selection was performed in the F3 population of a cross between IR- 64 and IET-14444 to detect lines containing multiple resistance genes. Of t he 59 progeny lines analyzed, eight lines contained both the resistance gen es, xa5 and Xa4.