pTA248 is a PCR marker linked to the Xa 21 gene. In this paper, some issues about breeding rice resistante to bacterial blight through the selection of pTA248 with 7 donors and recipients of Xa 21 gene, and the F 1, F 2, F 3 populations of 3 combinations of R( Xa 21)×S as are discussed. These inclucle the polymorphism between the donor and the recipient of Xa 21 gene, the linkage between pTA248 and Xa 21 gene, and the accuracy of the selection of pTA248. The results show that pTA248 repre...