Breeding of suitable sweet sorghum (Sorghum bicolor L. Moench) cultivars can boost biofuel production and farmer income in southern Africa. To generate the information necessary for breeding, eight female lines were crossed with 10 male lines in a North Carolina design II mating scheme. The 80 hybrids, parents and check varieties were evaluated across four environments during 2008 to 2009. Analyses were performed in GenStat. Genotype stability was assessed using the genotype and genotype by environment interaction (GGE) biplot procedure. Results showed significant (P≤0.05) differences between genotypes for stem brix, stem biomass and associated traits. Hybrids were predominant in the top 20 ranked genotypes for stem brix and stem biomass, demonstrating their superiority. The entries attained yield advantage over standard check of up to 128% for stem sugar and 245% for stem biomass, indicating the potential for identifying cultivars for immediate use by farmers. The GGE biplot showed that the majority of the genotypes displayed general adaptation although specifically adapted ones were identified. Nine hybrids displayed above 10% positive higher-parent heterosis for stem brix and 16 hybrids for stem biomass. Three hybrids were common for both traits, indicating the gains that can be realised by developing hybrids. General and specific combining ability effects were significant for the major traits, confirming reports that genes with both additive and non-additive action controlled them. Therefore, a breeding programme for general adaptation that exploits both additive and non-additive gene action can result in the delivery of high yielding hybrid sweet sorghum cultivars.
Key words: Combining ability, genotype and genotype by environment (GGE), biplot, heterosis, sorghum hybrids, stem sugar traits.
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