Improving bacterial blight resistance of '6078', an elite restorer line ofhybrid rice, by molecular marker-assisted selection

Bacterial blight (BB), caused by Xanthomonas oryzae pv. oryzae (Xoo), is on e of the most devastating diseases of rice world-wide; it is also a serious problem of hybrid rice production in China. In this study, a molecular mar ker-assisted introgression of Xa21, a gene highly resistant to a broad spec trum of Xoo strains, from 'IRBB21' was performed to improve the BE resistan ce of '6078', a new restorer line with high yielding potential. The entire process took one generation of crossing followed by three generations of ba ckcrossing and one generation of selfing. The presence of Xa21 in each gene ration was determined by both polymerase chain reaction (PCR) and pathogen inoculation. Recombinations between Xa21 and flanking markers were identifi ed by PCR analysis. Background selection was conducted in BC1F1 and BC2F1 u sing amplified fragment length polymorphism (AFLP) markers detecting a tota l of 129 polymorphic bands between '6078' and 'IRBB21'. The individual sele cted in BC3F2, or '6078'(Xa21), carried a fragment of less than 3.8 cM from the donor line in the Xa21 region on chromosome 11, and about 98.8% of the generic background from the recurrent parent. The results showed that '607 8'(Xn21) had the same level and spectrum of BB resistance as the donor pare nt 'IRBB21', while maintaining the agronomic performance and combining abil ity of the original 6078. A significant increase in BE resistance was also achieved in the hybrid using 6078(Xa21) as the restorer line.