Inheritance of sex expression in castor (Ricinus communis L.)

Inheritance of percent pistillate whorls in castor through a 8 x 8 diallel was studied in six environments over two seasons. Both additive and non additive gene effects governed the inheritance of percent pistillate whorls at primary and SITI raceme. Estimates of combining ability and ratio of additive to total genotypic variance indicated importance of additive gene effects for inheritance of these traits. Non-additive gene effects were more sensitive to environmental changes. Newly developed pistillate line MCP-2 was found best general combiner for sex expression, all male parents had contributed towards maleness at primary and SITI raceme. Specific combining ability indicated MCP-2 x RG-125 as an unique cross combination in pistillate x male crosses since it had exhibited positive sea effects at primary and S₁T₁ raceme and amongst male x male crosses, epistatic gene action contributed for percent pistillate whorls. Generation mean analysis showed that both additive as well as non-additive gene effects governed the inheritance of percent pistillate whorls on primary raceme. In crosses VP-1 x RG-299, VP-1 x RG-184 and RG-184 x RG-299, additive (d) and additive x dominance 0) gene effects were responsible for inheritance of femaleness. In cross MCP-2 x RG-125 dominance x dominance (1), additive (d) and dominance (h) gene effects governed the pistillateness. Non-allelic additive x additive interaction (i) and dominance (h) gene effects had operated for inheritance of percent pistillate whorls in cross RG-125 x 846. Based on diallel and generation mean analysis it was concluded that percent pistillate whorls in castor is governed by additive and epistatic gene effects.