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

Abstract

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.

Genetic Potential of Tropically Adapted Exotic Maize (Zea mays L.) Heat-Tolerant Donor Lines in Sub-Tropical Breeding Programs

“…Therefore, hybridization and recurrent selection might be helpful for genetic enhancement of heat tolerance and superior performance under heat stress conditions [20]. The findings concur with several authors [17,19,22,[36][37][38] who reported significant GCA and SCA for grain yield under heat-stressed and optimal conditions. The significant GCA f and GCA m effects observed for grain yield under managed heat stress and optimal conditions imply that both parents contributed to the inheritance of grain yield in the hybrids under these conditions.…”

“…The differences in heritability values for grain yield observed under stress, optimal conditions, and across environments were in line with the reports of several researchers [11,22,47]. The higher value of broad-sense heritability for yield, under heat stress, optimal conditions, and across environments suggests that environmental effects had a small role in the variation observed [48].…”

“…Combining ability for heat tolerance in maize was studied by several researchers, and both additive and non-additive gene action were reported on the expression of grain yield, anthesis-silking interval, leaf firing, tassel blasting, and anthesis dates [15,21,22]. Studies conducted by Jodage et al and Chapman et al [15,21] showed that additive genetic effects play a major role in conditioning grain yield under heat stress conditions in tropical maize.…”

Heterotic Classification of Inbred Lines of Maize Based on Combining Ability for Kernel Yield

“…On contrary Riboniesa et al [14] classified 21 inbred lines using single tester and assigned 11 inbred lines in to two heterotic groups. Alphonse Nyombayire et al [15] classified 3 maize inbred lines (S4, S6 and S7) that were considered as testers discriminated the seven local lines into three heterotic groups. Elmyhun et al [16] Positive heterosis for kernel yield were reported by Ali et al [17] and Mideksa et al [18].The testers were able to classify 15 out of 27 inbred lines into heterotic groups A, B, and AB based on SCA effects presented in (Table 6).…”

Identification of promising parental lines and hybrids in sweet corn (Zea mays L. saccharata)

“…Most of the authors reported combining ability and heterosis studies in normal corn (Amegbor et al, 2020;Bisen et al, 2020;Elmyhun et al, 2020;Gramaje et al, 2020;Kamara et al, 2020;Keimeso et al, 2020;Khamphasan et al, 2020;Onejeme et al, 2020;Patil et al, 2020;Scaria., 2020;Upreti et al, 2020;Yu et al, 2020;Abdulazeez et al, 2021;Maphumulo et al, 2021;Nyombayire et al, 2021;Riacheet al, 2021) and very few authors ( Dermail et al, 2020;Ravikesavan et al, 2020;Vanipraveena et al, 2021) pertaining to sweet corn. Keeping up with the demand of sweet corn in the market, development of sweet corn hybrids is need of the hour.…”