Marker assisted introgression of blast (Pi-2 and Pi-54) genes in to the genetic background of elite, bacterial blight resistant indica rice variety, Improved Samba Mahsuri

Improved Samba Mahsuri (ISM), a bacterial blight (BB) resistant (possessing Xa21, xa13 and xa5), high-yielding rice variety possessing fine-grain type has been recently released for cultivation and is becoming increasingly popular across many parts of India. However, the new variety is highly susceptible to blast disease, which limits its spread. In the present study, we attempted to improve blast resistance of ISM by introgressing two major blast resistance genes (Pi-2 and Pi-54) by marker-assisted backcross breeding through two separate sets of backcrosses, one involving transfer of Pi-2 and another involving Pi-54. At each backcross generation, closely linked PCR-based markers were used to select plants possessing either Pi-2 (first cross) or Pi-54 (second cross) along with Xa21, xa13 and microsatellite markers polymorphic between donor and recurrent parents were used to select plants that have maximum contribution from the recurrent parent genome (background selection). Selected BC2F1 plant possessing Pi-2 was intercrossed with a selected BC2F1 plant possessing Pi-54 and the resultant intercross F1 was selfed to generate intercross F1 possessing the two blast and two BB resistance genes. The intercross F1s were then selfed to generate intercross F2s possessing different combination of resistance genes in homozygous condition including the four-gene pyramid lines. The homozygous lines were advanced further through pedigree method of selection. When selected gene-pyramid lines possessing both blast and BB resistance genes were screened against the two diseases, they exhibited high level of disease resistance. Further, all the gene-pyramid lines possessed grain type identical to ISM and yielded equivalent to or better than the original variety. This is the first report documenting the stacking of two major genes for blast (Pi-2 ? Pi-54) and two major genes for BB (Xa21 ? xa13) in rice through marker-assisted backcross breeding in a elite cultivar Improved Samba Mahsuri.