Pyramiding of bacterial blight resistance genes in rice: marker-assisted selection using RFLP and PCR

 DNA marker-assisted selection was used to pyramid four bacterial blight resistance genes, Xa-4, xa-5, xa-13 and Xa-21. Breeding lines with two, three and four resistance genes were developed and tested for resistance to the bacterial blight pathogen (Xanthomonas oryzae pv. oryzae). The pyramid lines showed a wider spectrum and a higher level of resistance than lines with only a single gene. To speed up the gene pyramiding process and to facilitate future marker-aided selection, we developed PCR markers for the two recessive genes, xa-5 and xa-13, and used these to survey a range of rice germplasm. The results of the germplasm survey will be useful for the selection of parents in breeding programs aimed at transferring these bacterial blight resistance genes from one varietal background to another.