Abstract
The studies were conducted during January 2005 to February 2008 at the research field of Bangladesh Agricultural Research Institute, Gazipur to assess genetic diversity, combining ability and heterosis in normal and quality protein maize (QPM) parents and hybrids in order to develop high yielding quality hybrids. The study area covered identification of normal and QPM parental lines through genetic diversity, hybridization among and between the selected lines to estimate gca, sca and heterotic effects for quantitative and qualitative traits in pursuit of exploiting high yielding qualitative hybrids. Based on per se performances and genetic diversity 14 inbred lines (7 QPM and 7 normal) out of 42 were selected for hybridization. The genetic studies showed both additive and non-additive gene actions in the inheritance of the studied characters, although there was preponderance of non-additive gene action. Higher scal effects for different characters appeared in high high or high average or average × average gca effects of the parents for QPM × QPM crosses, while it was in high × high or high x low or average average in case of normal × normal crosses, and high high or high x low or average average gca effects for QPM × normal crosses. Although mean heterosis for yield and most of the yield components showed negative values in QPM × QPM and normal x normal crosses, yet QPM × normal crosses showed high positive values for all of these traits. Though only a few hybrids showed high heterosis for yield in QPM x QPM and normal x normal crosses, but in case of QPM x normal crosses most of the hybrids expressed significantly higher heterosis over both the checks. The highest heterosis for kernel yield was 23.61% in QPM × normal cross followed by 9.71% in normal × normal and 6.35% in QPM × QPM cross over the commercial normal check variety, Pacific 11. Quality parameters like protein, lysine and tryptophan showed maximum heterosis of 29.28%, 42.31% and 40.91%, respectively in QPM × normal crosses over the same normal check. Besides, all the hybrids produced from QPM × normal cross exhibited significantly higher lysine and tryptophan content over the normal check, although they showed significant negative heterosis with QPM check variety, BARI hybrid maize 5. The hybrids of QPM × normal crosses also showed high positive mean heterosis for all the quality traits against normal check. For double crosses, the hybrids of (QPM × QPM) × (normal x normal) crosses exhibited significantly higher heterosis for yield and yield components over both the QPM and normal checks, although they showed significantly negative heterosis for qualitative traits against QPM check but expressed significant and positive heterosis over the normal check. The results suggest that maize yield could be effectively improved with adjustable good quality in single crosses of QPM × normal and in double crosses of (QPM × QPM) × (normal × normal) hybrids.