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Masters Degrees (Plant Breeding)

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Browsing Masters Degrees (Plant Breeding) by Author "Dlamini, Mandisa Noxolo."

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    Combining ability and genotype-by-environment Interaction analyses among early-to-medium maturing maize hybrids under drought and non-drought environments.
    (2021) Dlamini, Mandisa Noxolo.; Sibiya, Julia.; Musvosvi, Cousin.
    Developing high yielding early to medium maturing maize hybrids for Southern Africa represents an effective way to contribute to improving crop productivity in the face of climate change and unpredictable weather patterns. The objectives of this study were: (i) to determine combining ability and gene action among germplasm lines for grain yield (GY) and other traits under drought and non-drought conditions using the line x tester mating design (ii) to explore genotype-by-environment interaction (GEI) patterns of the developed hybrids and identify broadly and specifically adapted entries, with the intention of developing early to medium maturing hybrids for South Africa and the sub region. Twenty-three white maize inbred lines sourced from the International Maize and Wheat Improvement Center (CIMMYT) were crossed in a line x tester mating design involving 13 lines (females) and 10 testers (males), resulting in 122 successful single-cross (SC) hybrids. The SC hybrids and six commercial hybrid checks were evaluated in a 13x10 alpha lattice design, replicated twice under drought and non-drought conditions across three sites viz: Cedara Research Station, Ukulinga Research Farm and Makhathini Research Station over three seasons, (2018-2019 summer growing season, the 2019 offseason, and 2019-2020 summer growing season). Data for grain yield and its related traits was collected. Genetic analysis of the line x tester data followed a fixed effects model. The parents differed in general combining ability (GCA) effects for GY and other traits under drought and non-drought conditions. Likewise, the crosses varied in specific combining ability (SCA) effects for GY and other traits under the drought and non-drought regimes. Line CZL1380 and tester CML539 were good general combiners for GY under drought. Lines CML568, CKDHL0378, CKDHL0467, CML672, and CZL1380 and testers CML312 and CML547 had good GCA effect across non-drought regime. Two crosses, CML540 x CML547 and CKDHL0467 x CML312 had high SCA values for GY under drought and non-drought regimes. The additive type of gene action was predominant for days to anthesis (AD), days to silking (SD), anthesis-silking interval (ASI) plant height (PH), ear position (EPO), ears per plant (EPP), ear aspect (EA), grain texture (GTX), grain moisture (GMH), kernel row number (KRN), and shelling percentage (SHL) under drought, and for AD, SD, ear height (EH), EPO, EPP, EA, GTX, GMH, ear length (EL), kernels per ear row (KER), ear weight (EW), and hundred kernel weight (HKW) across non-drought conditions. Non-additive gene action prevailed for EH, EL, ear diameter (ED), KER, EW, HKW, and GY under drought and for ASI, PH, ED, KRN, SHL, and GY across non-drought conditions. The identified hybrids could be targeted for release as cultivars, and the types of gene action are practically relevant for improvement of early to medium maturing maize germplasm for Southern Africa. Grain yield data from the five environments was analysed to explore genotype by environment (GEI) among the developed hybrids and checks. Analysis of variance across all the environments showed huge environmental, genotypic and GEI effects, with the environment contributing the largest proportion of the variation followed by genotype and lastly GEI. The additive main and multiplicative interaction effects (AMMI) and the genotype and genotype-by-environment interaction (GGE) methods were employed on selected 62 entries to visualize the GEI patterns. The AMMI revealed that two interaction principal component axes (IPCA1 and IPCA2) were significant, and these contributed 50.32 % and 20.84%, respectively, to the total GEI variation. The AMMI1 revealed that hybrid MAK1-122 x CML545 was specifically adapted to drought conditions whereas hybrids CKDHL0467 x CML312 and CZL1380 x CML547 were broadly adapted. The identified two high yielding and broadly adapted experimental hybrids were superior to the best check WE3127 across all environments. Hybrids CML569 x CML566 and CKDHL0467 x CML547 were specifically adapted to irrigated conditions. The GGE-biplots had two principal components, PC1 and PC2, which together explained 69.87% of variation due to genotype and GEI. The GGE-biplots showed similar GEI patterns as AMMI, with the same hybrids identified as broadly and specifically adapted. The identified hybrids could be assessed further in multi-environmental and multiple stress trials to confirm their suitability under high and low input production systems in South Africa and the sub-region.