Marker-assisted pyramiding of major blast resistance genes in Swarna-Sub1, an elite rice variety ( Oryza sativa L.)

Swarna-Sub1, a ruling submergence tolerant variety of rice, showed a significant decrease in the yield in major blast disease prone areas, which is caused by fungus Magnaporthe oryzae ( Pyricularia oryzae ). To overcome this problem, three major blast resistance genes viz ., Pi1, Pi2, and Pi54 were pyramided through marker-assisted backcross breeding using donors, Swarna-LT (having Pi1 + Pi54 ) and Swarna-A51 (having Pi2 ). Foreground selection was carried out using molecular markers tightly linked to three blast resistance genes and also submergence tolerance for retaining the Sub1 gene in the recurrent parent. Based on disease resistance and agro-morphological performance of backcross-derived lines, we selected the best 25 plants of two- and three-gene pyramided BC 3 F 2 homozygous lines with a maximum of ~ 93.5% recurrent parent genome and were further advanced to the BC 3 F 5 generation. The stringent recurrent parent genome recovery analysis using SSR markers limited the linkage drag from a minimum of 0.2 Mb to a maximum of 2 Mb in all three-gene pyramided lines. The two and three blast resistance genes pyramided lines, i.e., SS30-24-82, SS30-24-73, and SS30-24-46, displayed a high level of blast resistance and submergence tolerance. The successful use of marker-assisted backcrossing strategy coupled with phenotypic selection helped in the development of Swarna-Sub1 lines having multiple blast resistance genes with superior agro-morphological and grain quality traits, which could serve as valuable genetic stocks in the rice breeding program.