Identification, molecular mapping and marker-assisted introgression of novel bacterial blight resistance genes from wild relatives of Oryza

Wild relatives of Oryza sativa are an important source of genes conferring resistance/tolerance to various biotic and abiotic stresses afflicting rice. With an objective to identify new sources of resistance to bacterial blight (BB), a set of wild rice accessions available at DRR were screened for BB resistance. An accession each of Oryza nivara (accession # IRGC105710), O. rufipogon (accession # IRGC86476) and O. longistaminata (accession # DRW26009) were observed to be highly resistant against multiple isolates of the bacterial blight pathogen. The resistant accessions were crossed with the BB susceptible cultivar TN1. The F1 plants obtained from the cross IRGC105710/TN1 were found to be resistant to BB, while the F1s derived from the cross IRGC86476/TN1 were susceptible, with both the F1s displaying partial spikelet sterility. F1s obtained from the cross DRW26009/TN1 were completely sterile. The F1s derived from the crosses IRGC105710/TN1 and IRGC86476/TN1 were backcrossed to generate BC1F2 and BC2F2 mapping populations, which were then progeny tested for BB resistance. A single dominant gene was observed to control resistance in IRGC105710, while a single recessive gene was observed to confer resistance in IRGC86476. The dominant gene present in the O. nivara accession was mapped on Chr. 7 in the vicinity of SSR markers RM20948, RM5711, RM21052, RM21064, RM21077, RMWR7.1, RM7.6, RMWR7.10, RM21122, RM21137, RM6728, and RM21260, with RMWR7.1 and RMWR7.6 flanking the gene closely within ∼ 1 cM interval. Similarly, the recessive gene present in IRGC86476 was mapped on Chr. 1 near the SSR markers RM10692, RM10702, RM8094, RM10727, RM10739, RM10748 and RM10761, with RM8094 and RM10727 closely flanking the gene. Using the tightly linked, flanking markers RMWR7.1 and RMWR7.6, the new gene from IRGC105710 was introgressed into an elite, fine-grained, high yielding rice variety Samba Mahsuri through markerassisted backcross breeding. The introgressed lines possessed high BB resistance and were observed to be identical to Samba Mahsuri in terms of grain quality and yield. Marker-assisted introgression of xaOr is in progress.