ABSTRACT
'Shuhui527' is a promising restorer line bred by Rice Research Institute of Sichuan Agricultural University in recent years. However, this line is susceptible to Bacterial Blight (BB), which limits its use. The IRBB60, from the International Rice Research Institute (IRRI), contains dominant genes Xa21 and Xa4 conferring resistance to BB. The objective of this study is to improve the BB resistance of 'Shuhui527' by introgressing Xa21 and Xa4, the two broad-spectrum BB resistance genes, into 'Shuhui527' with IRBB60 as the donor, pTA248 and MP12, linking tightly with Xa21 and Xa4 respectively as DNA markers. BC1 F1 progenies of (Shuhui527 x IRBB60), containing Xa21 and Xa4 identified using PCR screening and with agronomic traits including plant type, grain type and days to heading etc similar to those of 'Shuhui527', were subsequently backcrossed to 'Shuhui527' and self-pollinated to generate BC2 F1 and BC1 F2 . The BC3 F1 and BC3 F2 were subsequently developed using the same approach. Among the 20 BC3 F2 plants, homozygous Xa21 and Xa4,10 plants were the most similar to 'Shuhui527' in the agronomic traits, and were screened using 120 pairs SSR and 100 pairs RAPD markers. Based on the results of the background screening and the performance of the agronomic traits, 5 plants were identified as improved-'Shuhui527' and designated as 527R-5, 527R-6, 527R-8, 527R-9 and 527R-10. The improved-' Shuhui527' lines expressed high resistance to Xanthomonas oryzae pv . oryzae (Xoo) stains C I - C VII, P1 and P6. The evaluation of the polymorphisms and selection accuracies of pTA248 and MP12 demonstrated that the polymorphisms of the two markers were obvious and co-dominant and the accuracies were more than 97% and 83% respectively, indicating the two markers are good for Xa21 and Xa4 in Molecular Marker-assisted Selection.