|dc.description.abstract||Maize is a third important cereal crop in the world after wheat and rice. Its production is however hampered by both biotic and abiotic factors. Among the abiotic factors, heat stress has been reported to cause yield losses of about 1 to 1.7 % per day for every rise in temperature above 30◦C. Development of stress tolerant varieties would be a cheap input technology that would play a vital role in enhancing maize productivity. Understanding the type of gene action conditioning heat tolerance will help the breeder to know the type of breeding strategy to employ. The general objective was to conduct genetic analysis for heat tolerance in tropical maize and the specific objectives of this research were therefore (i) To identify desirable performing genotypes under heat stress (ii) To identify genotypes with good combining abilities under heat stressand (iii) To determine the type of gene action conditioning heat tolerance in tropical maize. To achieve these objectives, five maize inbred lines (L2; DTS 6,36; L5527; DTS 6,6 and DTS 6,92) with varying tolerance to heat stress were mated in a five by five half diallel. Their progeny were evaluated for heat stress in Lusitu with mean monthly temperature of over 30◦C and another set of crosses were planted at the University of Zambia field station with mean monthly temperature of 25 - 29◦C as a control. The experiment was laid as a randomised complete block design with two replications in each site. Highly significant differences (P ≤ 0.01) were obtained among genotypes in Lusitu with regards to total biomass, curling of leaves, chlorophyll concentration index (CCI), vigour and plant height. The genotypes P2 (DTS 6,36) x P4 (DTS 6,6) and P4 (DTS 6,6) x P5 (DTS 6,92)were identified as tolerant genotypes. Further analysis showed that parent P4 (DTS 6, 6) and P3 (L5527) were positively and negatively significantly different (P ≤ 0.01) from zero respectively with regards to total biomass, curling of leaves, root biomass, shoot biomass, CCI, vigour and plant height. Similarly, crosses P1 (L2) x P3 (L5527), P4 (DTS 6,6) x P5 (DTS 6,92 ) and P1 (L2) x P4 (DTS 6,6), P1( L2) x P5 (DTS 6,92 ) & P3 (L5527) x P2 (DTS 6,36) were positively and negatively significantly different (P≤0.01) from zero respectively with regards to total biomass, root biomass and shoot biomass. Genotypes with good general combining abilities and specific combining abilities were inbred line P4 (DTS 6,6)and crosses P1(L2) x P3 (L5527) &P4 (DTS 6,6) x P5(DTS 6,92) respectively. The results of baker’s ratio obtained for response to all measured parameters in Lusitu was greater than 0.87. This reviewed that additive gene action was more important in conditioning the response of these traits to heat tolerance.
Key words: Heat tolerance, combining abilities, gene action, inbred lines||en