Gene action and heterosis for agro-nutritional quality traits of maize hybrids in humid agro-ecologies of Nigeria

Maize is a staple food of sub-Saharan African (SSA) populace but deficient in protein. Quality protein maize (QPM) has been developed to contain essential amino acids including lysine and tryptophan to alleviate malnutrition in SSA. This study was conducted to assess general and specific combining ability (GCA and SCA) effects, gene actions and heterosis among QPM hybrids for lysine and tryptophan at three locations in humid agro-ecologies of Nigeria. Grains from sib-mated full-sibs were analysed for lysine and tryptophan among ten inbreds, 45 hybrids generated by half-diallel and two checks. Results showed lysine and tryptophan contents ranged from 2.71% - 0.73% (Kishi) to 3.41% - 0.96% (Ibadan). Gene actions for expression of lysine and tryptophan varied with location; thus, additive gene action was preponderance in inheritance of lysine and tryptophan in Ibadan and Ile-Ife, whereas non-additive gene action was involved in inheritance of these traits in Kishi. Inbreds TZEEQI-8, TZEEQI3, TZEEQI-10, TZEEQI-12, TZEEQI-2 were best combiners for lysine and tryptophan. Hybrids TZEEQI-8?TZEEQI-16, TZEEQI-2?TZEEQI-12, TZEEQI 10?TZEEQI-7,TZEEQI-10?TZEEQI-12 and TZEEQI-8?TZEEQI-12 were adjudged as the top five hybrids for exhibiting positive and significant standard heterosis over commercial check with a range of 12.8%-16.7% for lysine and 15.4%-20.0% for tryptophan across locations. The relationship between grain yield with lysine and tryptophan was negative and significant across locations. Hence, breeding for high yielding QPM genotypes with high lysine and tryptophan contents at the same time, requires careful monitoring of lysine and tryptophan contents in the laboratory.