Inheritance and combining ability study on drought tolerance and grain yield among early maturing inbred lines of maize (Zea mays L.)

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November, 2016
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Utilization of stress tolerant maize is key to sustainable production and food security. Limited knowledge on genetics of drought tolerance hampers development of drought tolerant varieties. The objective of this study was to study inheritance and combining ability of drought tolerance among early inbred lines of maize. Five inbred lines were mated in full diallel in 2015 major season. The resultant 20 hybrids, 5 parents and 2 checks were evaluated under drought stress and well watered conditions in a screen house. Data was collected on days to 50% tasseling (DT 50%), days to 50% silking (DS 50%), anthesis-silking interval (ASI), leaf rolling, leaf senescence, plant aspect (PASP), plant height (PHT), ear height (EHT), ears per plant (EPP), ear weight, hundred grain weight (100 GW) and grain yield per hectare (GY). Drought condition was induced 40 days after planting but watering was continued once per week till maturity. Results from combined ANOVA showed there was high and significant (p<0.01) level of genetic variability among parental lines and hybrids used in all the traits studied except DT 50%, PHT, EHT, EPP and 100 GW. There were significant variation in the combining ability of the inbreds under both drought stress and well watered conditions. Both additive and non-additive gene actions were important as well as GCA/SCA ratio variance. Therefore the predominance of GCA over SCA mean squares for DT 50%, DS 50%, ASI, leaf senescence, PHT, EHT, and 100 GW indicates that additive genetic action was more important than non-additive genetic action for inheritance of these traits. Lines TZEI-23 (215.22) and TZEI-25 (76.84) had the highest and highly significant (p<0.01) positive GCA effects for GY under drought while TZEI-25 (350.77) and TZEI-124 (237.51) had positive GCA effects under well watered condition. Hybrids TZEI-25 x TZEI-13 showed the highest positive and highly significant (p<0.01) SCA effects for GY (385.74) followed by its reciprocal TZEI-13 x TZEI-25 (311.49) under water stress while under well watered condition TZEI-13 x TZEI-124 (1132.01), TZEI-17 x TZEI-13 (789.01) and TZEI-17 x TZEI-124 (789.01) were the highest and were highly significant (p<0.01). High broad sense heritability was observed for almost all the traits. High narrow sense heritability were observed in only DT 50% (0.69), DS 50% (0.80) and leaf senescence (0.61) under drought condition. Eighteen hybrids had positive high parent heterosis (HPH) under water stress and ranged from 47.94% (TZEI-124 x TZEI-17) to 364.48% (TZEI-13 x TZEI-25) while 19 hybrids exhibited HPH under well watered condition and ranged from 19.74% (TZEI-13 x TZEI-25) to 429.50% (TZEI-124 x TZEI-13) for GY. High parent heterosis were obtained for TZEI-13 x TZEI-25 in GY, ear weight, PAST, leaf senescence, DT 50% and DS 50%, and for TZEI-124 x TZEI-13 in GY, ear weight, PHT, EHT, PAST, DT 50% and DS 50%. Desirable heterotic levels in ASI, DT 50%, DS 50% and PHT are of tremendous advantage in areas with marginal rainfall. Nineteen hybrids scored positive mid-parent heterosis under drought condition as well as under well watered condition for GY and the increase under drought ranged from 5.48% (TZEI-17 x TZEI-13) to 369.90% (TZEI-13 x TZEI-25) and from 58.17% (TZEI-25 x TZEI-23) to 489.76% (TZEI-13 x TZEI-124) under well watered condition. The lines TZEI-23 and TZEI-25 were identified as the best general combiners respectively under drought and well watered condition. The highest HPH were observed in many traits for TZEI-13 x TZEI-25 and TZEI-124 x TZEI-13. It is recommended these hybrids are further evaluated in different environments for release to farmers to increase yield.
A thesis submitted to the Department of Crop and Soil Sciences, Faculty of Agriculture, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana in partial fulfillment of the requirements for the degree of Master of Philosophy in Plant Breeding,