Genetics of fertility restoration of 'WA'-based cytoplasmic male sterility system in rice (Oryza sativa) using indica/japonica derivative restorers

Exploitation of the higher degree of heterosis manifested in inter sub-specific (indica and indica/japonica) derivatives is one of the current trends in hybrid rice breeding. The success in developing indica/japonica hybrids using new plant type restorers developed from indica/japonica derivatives largely depends on the availability of effective restorers and knowledge of the genetics of fertility restoration of such derivative lines. A study using three indica/japonica restorers (P1277-100, P1266-89, and P1266-8) and three 'WA'-type cytoplasmic male sterile lines (Pusa 3A, Pusa 5A, and Pusa 6A) revealed that two or three major genes govern the fertility restoration, with epistatic interactions that differed from cross to cross. Crosses Pusa 6A/P1277-100 and Pusa 3A/P1266-89 showed a segregation ratio of 12:3:1 and 2:1:1 in F-2 and BC1 generations, respectively, for pollen fertility, indicating two major genes with dominant epistasis involved in fertility restoration. The restorer P1266-89, when crossed with Pusa 5A, segregated in different digenic ratios of 9:3:4 and 1:1:2 in F-2 and BC1 generations, respectively, for pollen fertility, indicating two major genes with recessive epistasis involved in fertility restoration. The same restorer P1266-89 when crossed with Pusa 6A, segregated in ratios of 27:30:7 and 1:2:1 in F-2 and BC1 generations, respectively, indicating three major genes governing fertility restoration. Restorer P1266-8 when crossed with Pusa 5A and Pusa 6A, gave the same segregation ratios of 27:30:7 in F-2 and 1:2:1 in BC1 generation, indicating that fertility restoration is also governed by three major genes.