Path coefficient analysis and combining ability between quality protein and pro-vitamin - a maize lines for yield and secondary traits.
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In most countries, white maize varieties are more preferred than the yellow/orange maize. Unfortunately, normal yellow and white maize lacks vitamin A which is crucial mainly for sight as well as growth and immunity. Sub-Saharan African (SSA) countries are largely dependent on maize as their meals are predominantly made from maize, and vitamin A deficiency (VAD) is a progressing problem in these countries. In the biofortified orange maize, vitamin A occurs in the form of pro-vitamin A (PVA) carotenoids. This pro-vitamin A maize is being used to alleviate the problem of VAD. Normal maize is also deficient in two essential amino acids, namely lysine and tryptophan that cannot be synthesised by the body. Quality protein maize (QPM) was developed from a mutant maize type that is rich in the essential amino acids, tryptophan and lysine. These two essential amino acids are required in the body for the formation of proteins which reduces the occurrence of protein deficiencies such as kwashiorkor in children. In addition to the nutritional insecurity that is being faced in SSA countries, maize that is being produced remains insufficient to sustain the populations as they are increasing tremendously. Development of high yielding and adaptable maize hybrids with better nutritional quality in terms of vitamin A and quality protein traits by stacking genes for vitamin A and quality protein in single cross maize hybrids will help alleviate this problem. This study was conducted to establish the combining ability of exotic PVA with locally adapted QPM lines, combining ability of the locally adapted PVA maize with QPM lines and contribution of secondary traits to yield in PVA and QPM hybrids. Line by tester analysis was conducted for two experiments. The maize inbred lines used in this study were developed by a shuttle breeding programme at University of KwaZulu-Natal. In the first experiment, 26 lines were crossed to four testers and 70 selected hybrids, including one check which was repeated twice, were evaluated in another trial. The hybrids were planted at Ukulinga in the summer season of 2015/2016. A 10 X 7 row by column design was used. In the second experiment, 12 lines were crossed to four testers and 44 selected hybrids, including one check, were evaluated in a trial. The hybrids were planted at two sites, Cedara and Ukulinga in summer season of 2015/2016. A 4 X 11 row by column design was used. Recommended agronomic practices were implemented for all the sites. Data was collected using a CIMMYT iii protocol and subjected to statistical analyses using Breeding Management System which is linked to Breeding View package, ANOVA and REML packages in GENSTAT 17th edition. The experimental hybrids performed competitively against the check that was used. The outstanding performance of the hybrids was also displayed by the high genetic gains that were realized for the selected hybrids in both the trials. In the first experiment, hybrid 16XH49 was ranked as the highest yielding. In the second experiment, hybrids 16XP11 and 16XP33 were ranked the highest yielding for Ukulinga and Cedara, respectively. The general combining ability effects of lines were significant for grain yield and shelling percentage for both sites. Cultivar Superiority Analysis revealed that hybrids 16XP33, 16XP11 and 16XP29 were the most stable. Path coefficient analysis revealed significant association of secondary traits with grain yield. Traits such as ear height, plant height, field weight, number of ears per plot, shelling percentage, 100-grain weight and plant stand exhibited positive direct effects on grain yield. Selection of these traits would effectively cause an increase in grain yield. Field weight was found to be the most important trait contributing towards grain yield.