Development of Basmati lines by the introgression of three bacterial blight resistant genes through marker-assisted breeding

Basmati is a premium quality rice, famous for its aroma, fine grain, and excellent cooking qualities. However, it is highly susceptible to bacterial leaf blight (BLB). To develop BLB resistant Basmati rice varieties, we transferred three (03) BLB resistance genes namely Xa4, xa5, Xa21 from a coarse yet BLB-resistant variety, IRBB57, developed by International Rice Research Institute into fine-quality rice variety, Super Basmati, through marker-assisted breeding. The background parent genome was recovered performing several backcrosses using Super Basmati as a recurrent parent to restore the bona fide Basmati character. The introgression of BLB resistance genes was followed by foreground selection using DNA-markers tightly linked with BLB resistance genes. The recovery of the Basmati parent genome (Background Selection) was determined using two different marker systems. Simple Sequence Repeats and Single Nucleotide Polymorphism. Several Super Basmati Introgressed (SBIL) lines with the individual as well as different BLB resistance gene combinations were developed. The stable representative SBILs from single, double, and triple gene combinations showing > 90% parent genome recovery were further studied for different attributes particularly to determine their degree of tolerance to the bacterial blight that was studied at two different locations-Philippines and Pakistan. We observed that SBILs carrying a combination of xa5 + Xa21 and Xa4 + xa5 + Xa21 conferred broad-scale resistance against both the highly virulent Pakistani and Philippines Xanthomonas oryzae pv. oryzae strains. The marker-aided background selection coupled with stringent phenotypic selection as well as foreground selection using DNA markers tightly linked with grain quality ensured that SBILs possess the bona fide Basmati character. The performance of key agronomic traits in selected SBILs was comparable with the recurrent parent with no significant agronomic or yield penalty associated with incorporation of the resistance genes, confirming the linkage drag has been minimized. Therefore, in addition to sustaining Basmati rice yield against BLB, the SBILs developed in this study may represent a useful resource for transferring resistance to BLB-susceptible rice varieties.