Combining ability analysis and heterotic grouping for grain yield among maize inbred lines selected for the mid-altitude and highland zones of Rwanda

Development and identification of maize parental lines that belong to different heterotic groups is a fundamental requirement for any hybrid production programme. The objective of this study was, therefore, to determine combining ability, heterosis and heterotic patterns for grain yield among ten selected local (unknown heterotic groups) and exotic (known heterotic groups) maize inbred lines and their progenies under mid-altitude and highland conditions of Rwanda. Forty-five single crosses from a 10 x 10 half-diallel mating design plus three checks were tested in a 6 x 8 alpha-lattice design across twelve environments. General combining ability (GCA) and specific combining ability (SCA) effects were both highly significant (P<0.001-0.01), suggesting presence of both additive and non-additive gene effects. The percentage mid-parent heterosis (MPH) for grain yield ranged from 36.4to 267.7% with a mean of 164%, while high-parent heterosis (HPH) varied from 33.2% to 236% with a mean of 130.4%. Based on MPH, the seven local maize inbred lines were discriminated and assigned into four different heterotic groups (S4, S7, S4/S6 and S6/S7). The highest heterotic patterns were realized between tester S4 and tester S6 (hybrid S4/S6) and between group S7 and tester S4 (hybrid S2/S4). Identified patterns would be potentially useful for maize hybrid production in Rwanda. Similarly, the resulting hybrids could be recommended in sub-Saharan African regions with similar ecosystems. Significance of both additive and non-additive genetic effects in the current germplasm suggests that the Rwandan breeding programme could use both hybridization and recurrent selection methods.