Combining ability and stability of extra-early yellow inbred lines of maize (Zea mays L.) for grain yield in three agro-ecological zones of Ghana

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Maize (Zea mays L.) is an important cereal crop in Ghana with a wide adaptation to all agroecological zones. In Ghana, maize yield in farmers’ field is far less than the world’s average yield, producing just about 1.7 t/ha. This low yield could be attributed to a larger extent the effect of continuous use of traditional/unimproved and open-pollinated varieties (OPVs), climate change, low soil fertility etc. Thus, development of superior extra-early hybrid varieties with wide adaptation to the effects of climate change on the environment is important to alleviate this constraint and improve maize production. However, there is scanty information on combining abilities and mode of inheritance of grain yield (GY) of extra-early maturing yellow inbred lines of maize in Ghana for a successful hybrid development programme. The objectives of this research were (i) to determine the combining ability, genetic control and heritability of GY of 10 extra-early inbred lines of maize and (ii) to assess the stability of hybrids of the 10 extra-early inbred lines in three agro-ecological zones of Ghana. 45 single-cross hybrids were developed using 10×10 half-diallel approach. The single-cross hybrids were evaluated at three environments, Fumesua (Forest zone), Ejura (Forest-Transition zone) and Kpeve (CoastalSavannah zone). The experiment was laid-out in a Randomized Complete Block Design (RCBD) with three replications. Data were collected on GY, days to 50% silking (DS), days to 50% tasseling (DTAS), anthesis-silking interval (ASI), plant height (PHT), ear height (EHT), stalk lodging (STLG), root lodging (RTLG), husk cover (HUSK) and grain moisture (MO) . Analyses of data showed that, effects of General combining ability (GCA) and Specific combining ability (SCA) were important in modulating the inheritance of GY and other agronomic traits of the inbred lines. Mean squares of GCA and SCA effects showed preponderance of GCA over SCA for GY and other agronomic traits across environments. This suggested that the additive gene iii effect was more important than the non-additive gene effect in the inheritance of GY and other relevant agronomic traits. Significant mean squares of GCA×E interaction observed for GY and some relevant traits suggested variation in the combining abilities of inbred lines at different environments. However, significant mean squares of SCA×E interaction for GY and other traits also suggested variations in the expression of traits of the single-cross hybrids across the three research environments. The moderately high narrow-sense heritability (h 2 ) and genetic advance (GA) for GY indicated the important role of the additive gene action, thus, selection of the trait would be feasible. Single-cross hybrids 28 (TZEEI 78×TZEEI 66), 2 (TZEEI 64×TZEEI 61) and 41 (TZEEI 94×TZEEI 76) were observed as high yielding and most stable across the three environments and out-yielded the local check variety, ‘Abontem’ by 28%, 20% and 18%, respectively. Kpeve (Coastal-Savannah zone) was the most discriminative and representative environment for the hybrids, hence, represented an ideal environment for the hybrid genotypes. It is recommended that the high yielding and most stable hybrids should be extensively tested in on-farm trials before release to farmers.
This thesis is submitted to The School of Graduate Studies, Kwame Nkrumah University of Science and Technology, in partial fulfilment of the requirement for the degree of Master of Philosophy in Agronomy (Plant Breeding), 2016