Success in the development of rice hybrids largely depends on the availability of effective restorers and precise basic knowledge on the genetics of fertility restoration of CMS and restorer lines. In a study using twenty diverse restorers and five 'WA' type cytoplasmic genetic male sterile (CMS) line, revealed the fertility restoration to be governed by two major genes with epistatic interactions that differed from crosses to crosses. The inheritance of fertility restoration in CRMS 32A × AD 06084R and ten other cross combinations revealed an F2 segregation ratio of 12:3:1 (FF: SF: CS), indicating the involvement of two dominant genes which exhibit dominant epistasis. In COMS 24A x IET 20899R hybrid, pollen fertility of F2 segregation fell into the digenic ratio 9FF: 3SF: 4CS showed the involvement of digenic supplementary or an epistasis with recessive gene action. F2 segregation ratio of 9:6:1 with two dominant genes which exhibiting epistasis with incomplete dominance was observed in COMS 24A × IET 20898 R and fourteen other cross combinations suggesting the two dominant genes Rf3 and Rf4 seem to control the fertility restoration. The differential mode of action of restorer genes could presumably be due to the influence of the female parent genotype or to the variable expression of the weaker gene in different genetic backgrounds. The differential segregation behaviour could also be due to the existence of certain modifiers influencing the penetrance and expressivity of the fertility-restorer genes.
hybrid rice, fertility restoration, dominant epistasis, incomplete dominance
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