Diallel analysis of extra early maize (Zea Mays l.) Inbred lines for drought and low nitrogen tolerance

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OCTOBER, 2016.
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The importance of maize has extended beyond human consumption into livestock feeds and industrial uses in sub-Saharan Africa. However, increasing drought and infertile soils (Low-N) have become important abiotic stresses affecting maize production. Varieties with improved water use efficiency and/or nitrogen would be beneficial for subsistence farmers via reduced production cost. Unfortunately, few breeding programs focus attention on breeding for low N and drought stress conditions. Hence, little is known about the genetic control and heritability to drought and low-N tolerance in maize. The study sought to improve maize production and productivity in the low rainfall zones of Ghana. Five parental inbred lines TZEEI-6, TZEEI-21, TZEEI-29, TZEEI-38, and TZEEI-76 were crossed in a complete diallel mating design and the resulting F1 hybrids were evaluated in four environments (optimal-N and low-N, well-watered and induced drought stress). The performance of hybrids varied significantly in different environments with respects to yield and contributing characters. Non-additive gene action controlled grain yield under low-N stress and optimal-N conditions and biomass yield under drought stress and well-watered conditions. Additive gene action controlled anthesis-silking interval, leaf senescence, leaf chlorophyll content, and ears per plant under low-N stress. Under managed drought stress, additive gene action was only important for days to silking, anthesis-silking interval, and tassel blasting. The inbred lines TZEEI-76 and TZEEI-21 were the best combiners for grain and biomass yield under low-N and drought stress. The best combiner under low-N stress for anthesis-silking interval was TZEE38, for plant height and leaf senescence was TZEEI-76, and for leaf chlorophyll content was TZEEI-29. The best combiner under drought stress for anthesis-silking interval, leaf senescence, leaf chlorophyll content, and tassel blasting was TZEEI-21. Desirable SCA effects were found for the crosses TZEEI-21×TZEEI-38, TZEEI-21×TZEEI-76, TZEEI-29×TZEEI-76, and TZEEI-38×TZEEI-76 under both stressed and non-stress conditions. Hybrid crosses TZEEI-6×TZEEI-29, TZEEI-6×TZEEI-76, and TZEEI-21×TZEEI-29 had desirable SCA estimates under drought stress. Hybrid crosses TZEEI-29×TZEEI-38 and TZEEI-29×TZEEI-6 had desirable SCA estimates for low-N. The cross TZEEI-29×TZEEI-38 had the highest heterosis under low-N stress while TZEEI-29×TZEEI-21 had the highest heterosis under drought stress. The narrow sense heritability of secondary traits; anthesis-silking interval, leaf senescence, and leaf chlorophyll content were higher under stressed conditions than non-stressed conditions. Significant correlation (p<0.05) was observed between yield and secondary traits; anthesis-silking interval, leaf senescence, and leaf chlorophyll content under low-N and drought stress environments. Across stress environments, leaf chlorophyll content and leaf senescence were significant (p<0.001). Hybrids selection combining tolerance to both stress conditions in order to stabilize yield on farmers’ field should concentrate on combining mean yield performance with positive leaf chlorophyll content and negative leaf senescence.
A thesis submitted to The Department of Crop and Soil Sciences, Faculty of Agriculture, Kwame Nkrumah University of Science and Technology, Kumasi, Ghana in partial fulfilment of the requirements for the degree of Masters of Philosophy in Plant Breeding,