Combining Ability, Gene Action and Heterosis in Maize (Zea mays L.) under Drought Stress

Combining ability, gene action and heterosis for grain yield and yield contributing traits were studied under drought stress at flowering in maize. The experiment was conducted at Institute for Agricultural Research farms, located at Samaru (11o11ʹN; 07o38ʹE) and Kadawa (11o39ʹN; 08o02ʹE) in Nigeria during the 2012/2013 dry season. Seven drought susceptible maize inbred lines used as female parents (designated as S1-S7) and six drought tolerant maize inbred lines used male parents (designated as P1, P2, P3, P4, P7 and P8) were crossed in North Carolina mating design II to generate 42 F1 hybrids. The evaluation trial was laid out using simple lattice design replicated two times. Data were collected on days to flowering, plant and ear heights, leaf senescence, number of ears per plant and grain yield. Results of the combining ability analysis revealed that both additive and dominance gene actions were responsible for the control of the traits. However, the effects of dominance gene action were preponderant in the genetic control of all the traits. The study showed that S7 and P8 were the best male and female general combiners among the parents, respectively. The cross S7 x P8 was the best among the hybrids having the highest desirable specific combining ability effect for grain yield. The hybrid also recorded high parent heterosis in terms of grain yield (133.33%) and days to 50% tasseling (-13.55%). It was concluded that these parental lines can be desirable for inclusion in breeding program since they may contribute favorable alleles in the synthesis of new varieties of this very important crop for drought stress environments.