Heterotic Groups, Gene Action and Heterosis Among Maize Inbred Lines Selected for the Major Agro-ecologies of Rwanda

Maize breeding programmes exploit inbred lines with superior combining ability for grain yield and other agronomic traits to create competitive hybrids. Therefore, the objectives of this study were to determine heterotic groups of locally developed maize inbred lines, their heterotic relationships, with exotic testers as well as the gene action controlling grain yield. Nineteen maize inbred lines were crossed to four testers, based on a line x tester mating scheme resulting in 76 test crosses. These crosses were evaluated together with four checks in 10 x 8 α-lattice design across four locations in 2015B and 2016A seasons. Both additive and non-additive gene action were important for grain yield with preponderance of additive gene action. The most desirable GCA effects for grain yield were realized in inbred line 8 while the highest desirable SCA effects were displayed by the test cross 18xT1. Generally, most of the inbred lines exhibited positive heterosis with all testers. However, there was more aligning firstly towards tester T2 and then to T3. The highest heterosis was displayed by the combination of inbred line 8 with 3. Regardless of the heterotic grouping method applied, the inbred lines were discriminated into different heterotic groups; two and nine heterotic groups were identified based on standard heterosis and SCA effects; respectively. The information generated would be useful in optimizing the maize hybrid breeding programme in Rwanda and for other researchers for high yielding maize variety development.