combining ability of kernel quality and some agronomic characteristics in quality protein maize (QPM) and non-QPM inbred
Date
2011-02-28
Authors
Mutimaamba, Charles
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Abstract
Maize is the principle staple food and source of protein and calories for millions of people in Southern Africa. Common maize is deficient in lysine and tryptophan and thus predisposes mothers and children to the risk of malnutrition. the consumption of quality protein maize (QPM), which has twice the lysine and tryptophan levels and same appearance and taste as common maize can potentially avert this risk. The national Program in Zimbabwe is currenttly using QPM inbred lines sourced from CIMMYT as donors for converting its elite non-QPM inbred lines to QPM as well as developing new ones. The donor capability of these QPM lines and their compatibilty with the national program elite inbred lines has never been systematically tested and validated. The current study was conducted to identify appropriate QPM donor inbred lines for use in the development of new inbred lines and the conversion of existing elite non-QPM in bred lines to QPM through endosperm phenotyping and testing for agronomic adaptability to stress and non-stress environments.Five white QPM inbred lines were crossed to twelve non-QPM yellow inbred lines following a modified North Carolina Design ii in which each line was not used strictly as male or female. The thirty-five hybrids were evaluated in an alpha lattice design with three replications at four sites in winter 2009. The study involved the assessment of the relative importance of general (GCA) and specific combining ability (SCA) effects, addictive and dominance gene action, and mid-parent heterosis in the phenotype expression of endosperm modification (MOD), levels of tryptophan (TRP), lysine (LYS) and protein (PROT): grain yield (GY), anthesis date (AD) and anthesis-silking interval (ASI) among inbred lines. On the basis of GCA effects, line CML511 was the best donor for MOD, LYS and PROT, and gave good GCA effects for the highest number of agronomic traits and environments. Line CZL082 was the second best donor for MOD. TRY and LYS. Line HX482P was the best general combiner in terms of desirable GCA effects for kernel quality and agronomic traits under more environments followed by line L7 which outperformed the other lines in terms of number of traits with desirable GCA effects. In terms of SCA effects, line CZL082 was the best donors because it was involved in more cross combinations with desirable SCA effects for kernel quality and agronomic traits under more environments. Line CML511 was the secondbest best donor given that it was involved in cross combinations that had the best SCA effects for MOD and LYS. Line 7 was the most outstanding line for giving the highest number fo traits with desirable SCA effects for agronomic traits in addition to MOD. Line CML511 was a constituent parent in separate cross combinations with the highest means for MOD and PROT. On the basis of mid-parent heterosis, line CML511 was the best donor for featuring in crosses with the highest positive mid-parent heterosis for mOD. Line EL77P and L7 had the best mid-parent heterosis by virtue of being constituent parents in the best five endosperm-modified hybrids. the mid-parent heterosis of two of five least modifield crosses was higher for TRP, LYS and PROT than that for the best modified hybrids, with line CML511 featuring in one of the crosses. Additive genetic effects were preponderant in the control of all kernel quality traits. Dominance gene action was predominant in influencing GY under MSV disease conditions and across all sites, while addictive genetic effects were more important in controlling this traits under optimum conditions and drought stress. Dominance gene action was predominant in controlling AD under optimum conditions whereas additive genetic effects were preponderant in governing the same trait under MSV disease. Both additive and dominance gene action were dominant in the control of ASI underall environments except MSV disease. Maternal additive gene action was predominant in the genetic control of ASI under all conditions besides MSV disease. Narrow sense and broad sense heritability were low for kernel quality traits and GY, while narrow sense heritability was medium for AD and low for ASI under drought stress. broad sense heritability was high for both AD and ASI but medium for GY under stress. lines CZL082 and CML511 were therefore identified on the basis of GCA and SCA effects, mid-parent heterosis and mean performance as the most appropriate QPM donors for line conversion and recycling of non-QPM inbred lines in the national program.
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Keywords
quality protein maize , non-quality protein maize , quality protein maize and non-quality protein maize inbred lines , combining ability of kernel quality