Development of Basmati-Derived Rice Lines for Grain Quality and Resistance to Bacterial Blight

Basmati rice is a premium class of aromatic rice grown traditionally in Pakistan and India, but is susceptible to bacterial blight (BB) caused by Xanthomonas oryzae pv. oryzae (Xoo). Molecular markers linked to BB resistance genes (Xa genes) and genes for aroma (fgr genes) were utilized in a marker-aided selection program to develop elite breeding lines with broad-spectrum resistance to bacterial blight and aroma. Sequence tagged site (STS) and simple sequence repeat (SSR) markers were used to detect the genes for BB and aroma, respectively. A cross was made between a Basmati-derived line IR 71730-51-2 and IRBB60 (а pyramided line containing Xa4, ха5, ха13 and Xa21 genes) at Plant Breeding, Genetics and Biotechnology Division of the International Rice Research Institute (IRRI), Philippines. Phenotypic selection was practiced until F8 when genotyping for Xa genes and fgr gene was performed. While one gene might mask the expression of another gene, markers linked to resistance genes helped the pyramiding of target genes. The combination of Xa genes provided a wider spectrum of resistance to Xoo in the Philippines; singly, Xa21 was the most effective, followed by xa5. Two, three and four gene pyramids of bacterial blight resistance genes had been introgressed from IRBB60 donor to five Basmati-derived rice lines (three lines having Xa4 and Xa21, one line having Xa4, xa5, and xa13 and one line having Xа4, ха5, xa13, and Xa21 genes). Among them, two lines possessed fgr gene for aroma. A set of 200 recombinant inbred lines (RILs) was also developed through single seed descent method and was evaluated for BB resistance, six agronomic traits, six physicochemical characteristics and QTL analysis of grain quality traits. Some promising lines were identified with genes for aroma and BB along with good agronomic performance and other grain quality traits. These elite materials were evaluated in large replicated yield trials. To map the genes/QTLs for grain quality traits, eleven QTLs were identified on 3 different chromosomes. Three QTLs for aroma in chromosome 8, two QTLs in chromosome 6 and one in chromosome 7 for amylose, two QTLs in chromosome 6 for gelatinization temperature, and one QTL each in chromosome 7 for grain length, grain width and grain length-width-ratio were detected from these 200 Basmati-derived RILs population. These elite lines could be readily used in breeding programs to transfer BB and aroma genes and other grain quality traits into aromatic rices.