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Ascertaining the relationship of genetic diversity and combining ability would aid the design of a breeding strategy for maize hybrids. Twelve tropical maize inbreds were crossed in a half-diallel to study gene action for yield and other traits and also to determine the relationship between heterosis, combining ability for grain yield and molecular genetic distance in the set of lines. Sixty-six crosses and their 12 parental lines were evaluated in five Kenyan locations in 2011 and 2012. Genetic distances between lines was quantified using 28 SSR markers. General combining ability (GCA) and specific combining ability (SCA) mean squares were both important for grain yield and other traits. However, SCA was more important than GCA for grain yield. Line C92 had the best GCA effects (0.63; p < 0.001), whereas MUL71 × OSU23i (1.11; p < 0.01) had the highest SCA. The correlation coefficient between genetic distance (GD) and SCA was high, positive and significant (0.62; p < 0.001), as was that between GD and het...

In sub-Saharan Africa, maize (Zea mays L.) is produced in very diverse environments, which often results in complex genotype-by-environment (G × E) interactions. The aim of the study was to identify genotypes with broad and specific adaptation and high-performance environments that offer the best discrimination for selection and assess parents’ contribution to hybrid stability. Sixty-six F1 maize hybrids developed from a 12 × 12 half-diallel were evaluated at four locations in Kenya across two seasons to study the G × E patterns for grain yield and other agronomic traits. The genotype and genotype-by-environment interaction (GGE) biplot method was used for graphical display of data. Stability of combining ability effects was examined using rank variance and Wricke’s ecovalence. Environments contributed moderately (44%) to yield variability while the effects of G × E interaction (23%) and genotypes (21%) were almost equal. The eight environments were divided into two mega-environments, the first re...

Stem borers, Busseola fusca (Fuller) Noctuidae, Lepidoptera and Chilo partellus (Swinhoe) Pyralidae, Lepidoptera, are serious insect pests of maize. However, genotypes showing exclusive resistance to each of these borers and with resistance to both species have not been identified in Kenya. The objective of this study was to evaluate tropical maize inbred lines for resistance to the two species. 112 maize inbred lines were artificially infested with the stem borers at three sites in Kenya. Each row of each line received three different treatments in different parts, namely infestation with B. fusca larvae, infestation with C. partellus larvae, and protection with beta 25 g/L cyfluthrin pesticide. Data was collected on leaf feeding damage rating, cumulative stem tunnel length, number of exit holes, number of dead-hearts, stalk strength and selected agronomic traits. There were significant differences among the test genotypes, (p

The spotted stem borer, Chilo partellus, Swinhoe (Lepidoptera, Crambidae) is one of the most destructive insect pests of maize in tropical environments. However, the combining ability and heterotic orientation of the germplasm for grain yield and borer resistance is limited. The objective of this study was to determine combining ability and heterotic orientation of new maize inbred lines under C. partellus infestation. Sixty six (66) inbred lines were crossed to two single cross testers in a line x tester mating scheme. The 132 testcross hybrids and four checks were evaluated at three locations in Kenya under C. partellus infestation. General and specific combining ability effects were significant for C. partellus stem borer resistance traits and grain yield, suggesting the importance of both additive and non-additive gene effects for these traits. Heterotic classification of lines was done based on both heterosis and specific combining ability data. Based on heterosis for grain yield data at Embu, 15 lines were allocated to group A, 18 to group B and 12 to group AB. At Kakamega, 26 lines were oriented towards group A, 19 to group B and 9 to group AB. At Kiboko, 15 lines were inclined towards group A, 18 to group B and 11 to group AB, whilst the remainder could not be classified. Based on the SCA estimates, at Embu, 10 lines revealed positive SCA effects with both testers and were considered to be AB-oriented while 8, and 1 lines were oriented towards A, and B, respectively. A similar trend was detected at Kakamega and Kiboko. The identified lines and heterotic groups would be used by hybrid maize programs where C. partellus stem borers occur exclusively or in league with other stem borers. Key words: Tropical maize, maize breeding, biotic and abiotic stresses tolerance.