ABSTRACTThe genetics of drought tolerance in maize was studied using seven drought susceptible maize inbred lines as female parents and six drought tolerant maize inbred lines as male parents, which were mated in a North Carolina Design II fashion. The resultant 42 F1 hybrids, 13 parents and a check were evaluated at Samaru and Kadawa under non-stress, intermediate stress and severe water stress conditions in 2012/2013 dry season to determine their genetic variability, character association, combining abilities, heritability and heterosis. Significant differences were observed among genotypes for most of the traits studied under the different moisture conditions. Genotype x location interaction was also significant for most of the traits studied. The top performing hybrids for grain yield across locations were S3 x P3 (5878kg/ha) under non-stress and S7 x P8 (3389kg/ha and 2111kg/ha) under intermediate and severe stress conditions, respectively. Overall, the grain yield was reduced by 45% under intermediate stress and 70% under severe stress of what the average yield would have been under non-stress condition across the locations. High values of both genotypic and phenotypic coefficients of variation were obtained for grain yield, leaf senescence, anthesis-silking interval and number of ears per plant under the non-stress and water stress conditions. Moderate to high broad sense heritability were observed for all the traits studied. The broad sense heritability for days to 50% tasseling, days to 50% silking and grain yield decreased with increasing stress whereas, the heritability of anthesis-silking interval, plant height, ear height, leaf senescence and number of ears per plant increased with increasing stress. Narrow sense heritability was low for all the traits under the different conditions and ranged from 2.89% to 20.48%, 4.11% to 16.91% and 1.95% to 14.88% under non-stress, intermediate and severe stress conditions across locations, respectively. Days to 50% tasseling, days to 50% silking and anthesis-silking interval viii were negatively correlated with grain yield while plant height, ear height and number of ears per plant were positively correlated with grain yield under the different conditions. Combining ability analysis showed that both additive and dominance gene actions were important for the inheritance of all the traits. The comparative variance due to additive and dominance revealed predominance of dominance gene action for all the traits studied. The ratio of additive to dominance variance portrays the importance and the predominance of dominance genetic effects as all the ratios were less than unity. The GCA status of parents revealed that S7 among females and P8 among males as good general combiners for grain yield and other traits. Among the 42 hybrids, only S7 x P8 exhibited the highest positive SCA effects and high parent heterosis for grain yield of 58.33%, 68.79% and 133.33% under severe, intermediate and non-stress conditions across the locations, respectively. These findings will be useful in planning maize breeding programmes for drought tolerance.
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