Marker-assisted introgression of genes conferring resistance against bacterial blight & blast into RPHR-1005, the elite restorer line of the popular rice hybrid, DRRH-3

RPHR-1005 is a stable, elite restorer line of rice possessing highly desirable medium-slender grain type and is the male parent of the popular public bred hybrid DRRH-3. However, both RPHR-1005 and DRRH-3 are highly susceptible to major diseases like bacterial blight (BB) and blast. As genes conferring effective resistance are available against both BB and blast along with availability of gene-specific markers, the present study was carried out to introgress a major BB resistance gene, Xa21 and a major blast resistance gene, Pi2 into the genetic background of RPHR-1005 through marker-assisted backcross breeding. RPBio Patho-1, a breeding line in the genetic background of the popular variety, Samba Mahsuri and possessing Xa21 and Pi2 served as the donor. Marker-assisted backcross breeding strategy was deployed for targeted introgression of the two resistance genes into RPHR-1005. This involved two rounds of backcrossing and at each backcross generation, foreground selection was carried out using PCR based molecular markers specific for Xa21 (i.e. pTA248) and Pi2 (i.e. AP5659-5) along with the markers specific for the major fertility restorer genes, Rf3 (i.e. DRRM-RF3-10) and Rf4 (i.e. DRCG-RF4-14) and background selection was done using a set of 61 parental polymorphic SSR markers spread across the rice genome. At BC2F2, a single plant possessing all the targeted genes along with maximum recurrent parent genome recovery (~ 93.4%; plant # RP-9-27-79-179) was selected and advanced through selfing and pedigree-based selection for morphological traits. AT BC2F4, three lines, viz., RP-9-27-79-179-74-9, RP-9-27-79-179-74-79 and RP-9-27-79-179-74-105, possessing high level of resistance against BB and blast along with complete fertility restoration and all the elite features of RPHR-1005 were identified.