Use of morpho-physiological traits to enhance breeding for drought tolerance in tropical maize

This thesis contains four mutually reinforcing studies conducted with the aim of identifying the most effective secondary morphological traits and approaches that can be used to efficiently select for high yielding and drought tolerant maize genotypes. In objective one, a survey was conducted to gain insights into farmer views on factors that influence choice of varieties in maize dominated farming systems in drought prone areas and their implications to breeding. Objectives two and three aimed at determining the combining ability of the inbred lines, assess efficacy of secondary traits and selection indices during breeding as well as the mode of gene action conditioning drought tolerance. Objective four aimed at mapping quantitative trait loci conditioning secondary traits that are strongly correlated to grain yield under drought conditions. North Carolina Design II was used to develop hybrids which were evaluated under managed drought stress in the dry season by withdrawing irrigation 4 weeks before and after flowering. A 248 F2:3 population derived from a cross CML505 x CZL 00009 elite drought tolerant lines was evaluated under managed drought stress and used to map the QTL using 278 SNP markers. Results showed that farmers were willing to make trait trade-offs when selecting for drought tolerance related traits. Study 2 showed that selection indices STI and GMP were the most suitable to be used in tandem selection with ear per plant, anthesis silking interval and leaf senescence. Study three showed that GCA of secondary traits was predominant over SCA in drought environments while AMMI managed to separate genotype grain yield performance. In study 4, genetic maps covering 1238.8 cM on ten chromosomes were generated and 31 QTL mapped. One QTL position on chromosome seven mapped for both anthesis date and stem lodging. The implications of these finding on maize breeding for drought tolerance are discussed in detail in the thesis with three modified papers from the thesis chapters having been published in peer reviewed journals.