Genetics of fertility restoration of diverse cytosterile sources in rice (Oryza sativa L.)

The availability of stable cytoplasmic male sterility and fertility restoring system is vital for commercial exploitation of heterosis in rice. Inheritance study using four effective fertility restorers (BL-184-AR, IR-54742-22-19-3, NVSR-20 and Pusa Sugandha-5) and five diverse cytosterile sources (KJTCMS-6A-WA, RTN 2A-ARC, RTN 3A-Mutant of IR 62829B, RTN 13A-Gambiaca and RTN 17A-Dissi), their F₁, F₂ and BC₁ populations revealed that the fertility restoration was governed by two independent genes, one of which appeared to be stronger in action than other. Crosses KJTCMS-6A X IR-54742-22-19-3, RTN-2A X BL-184-AR and RTN-2A X NVSR-20, RTN-3A X BL-184-AR and RTN-13A X NVSR-20, showed segregating ratio of 12 (fertile): 3 (partially fertile + partially sterile): 1 (completely sterile plants) and 2 (fertile): 1 (partial sterile/fertile): 1 (sterile) in F₂ and BC₁ generations respectively, for pollen and spikelet fertility indicating two major genes with dominant epistasis. In case of crosses KJTCMS-6A X BL-184-AR and KJTCMS-6A X NVSR-20, RTN-13A X BL-184-AR, RTN-17A X BL-184-AR segregated in the ratio of 9:6:1 and 1:2:1 in F₂ and BC₁ generations respectively, for pollen and spikelet fertility indicating two major genes with epistasis and incomplete dominance. While crosses, KJTCMS-6A X Pusa Sugandha-5, RTN-2A X IR-54742-22-19-3 and RTN-2A X Pusa Sugandha-5, RTN-3A X IR-54742-22-19-3, RTN-3A X Pusa Sugandha-5 and RTN-3A X NVSR-20, RTN-13A X IR-54742-22-19-3, RTN-13A X Pusa Sugandha-5 and RTN-17A X IR-54742-22-19-3, RTN-17A X Pusa Sugandha-5, RTN-17A X NVSR-20, exhibited the restoration pattern fitted well in a segregation ratio of 9:3:4 and 1:1:2 in F₂ and BC₁ generations respectively, for pollen and spikelet fertility displaying an epistasis with recessive interaction. The mode of action of these genes were different in different restorer combinations with five different sources of cytoplasmic genetic male sterility. Change in fertility restoration by same restorer with CMS line of same source and of different source could either due to cytoplasmic genetic interactions of CMS line and fertility restoring genes or may be affected by modifier fertility restoring genes or may be affected by modifier genes.