Doctoral Degrees (Plant Sciences)
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Browsing Doctoral Degrees (Plant Sciences) by Subject "AMMI"
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Item Open Access Evaluation of South African high quality protein maize (Zea mays L.) inbred lines under optimum and low nitrogen conditions and the identification of suitable donor parents(University of the Free State, 2013-10) Masindeni, Dimakatso Roselina; Labuschagne, M. T.; Mashingaidze, K.; Van Biljon, A.English: Genetic improvement of QPM can assist to better the livelihoods of resource poor communities and farmers in SA who rely on maize. QPM germplasm from the ARC-GCI was evaluated to generate information to assist breeders in improving the breeding programme through designing efficient selection procedures that will reduce the time and cost required to develop lines with improved nutritional quality; in the process benefiting small-scale farmers. Pollen parent effect was determined by selfing and cross-pollinating 12 QPM inbred lines for tryptophan content. The two pollination methods did not differ significantly for tryptophan content. Single ANOVAs detected genotypic differences for grain quality traits, while combined ANOVAs across eight environments detected highly significant genotype, environment and GEI effects for all traits except endosperm hardness. The AMMI and GGE biplot analyses explained more than 60% of GEI variation. GGE biplots were the best for visualisation of environments and cultivar performance. AMMI and GGE biplots were similar in identifying high performing genotypes for all traits except for oil content, and the most stable genotypes except for starch and tryptophan content. The GGE biplots identified the ideal genotypes as KO54W, KO54W, Hans Male, SO503W and CML144 for QI, tryptophan, protein, oil and starch content respectively. GGE biplots identified Cedara optimum N as the most representative and discriminating environment for QI, tryptophan and starch content, Tshiombo optimum N for protein and Potchefstroom optimum N for oil content. Twenty QPM and non-QPM genotypes were evaluated under low and optimum N conditions in two locations and highly significant environment effects were observed for all traits, whilst significant genotypic differences and GEI were observed for tryptophan content and QI. Most of the traits improved with increased N level. QPM varieties performed significantly better than non-QPM varieties for tryptophan content and QI in all environments. Tryptophan content was highly significantly correlated with QI (r = 0.95, 0.98 and 0.97), while starch content was significantly negatively correlated with oil content (r = -0.72, -0.65 and -0.67) in low, optimum and across N environments. Line x tester analyses of QPM inbred lines showed highly significant GCA mean squares of lines and testers for most traits and highly significant SCA mean squares for all traits except endosperm hardness. Contribution of SCA (lines x testers), was higher than that of GCA for lines and testers for most traits, with contribution of between 29-83% to the sum of squares; except for endosperm hardness. For endosperm hardness GCA for tester was the highest contributor to total sum of squares by 50%. Larger GCA of females than males showed the importance of maternal effects in most of the traits. Among the testers CML144, SO607W and SO503W had the best GCA for the majority of the traits. Four crosses viz., K64R x SO503W, T1162W x RO452W, K64R x RO452W and K64R x SO713W were promising for endosperm hardness, tryptophan content, QI and protein content, respectively. In general RO452W was the best specific combiner. The present study provides novel results on pollination methods, GEI, AMMI and GGE analyses, line x tester analysis, and correlation of grain quality traits of QPM germplasm in SA.