Combining ability for stem borer resistance and heterotic orientation of maize inbred lines using CIMMYT single cross testers under Busseola fusca infestation

Abstract

The African stem borer, Busseola fusca Fuller, is one of the most devastating insect pests of maize in tropical environments. Understanding of combining ability and heterosis may be useful for designing insect resistant hybrids. However, among the adapted maize inbred lines used in this study, the combining ability and heterotic orientation for grain yield and borer resistance is not known. The objective of this study was to determine combining ability and heterotic orientation of maize inbred lines under B. fusca infestation. Sixty six inbred lines were crossed to two single cross testers from CIMMYT in accordance with the line 9 tester mating scheme. The 132 three-way testcross hybrids and four checks were evaluated at two locations in Kenya. Data were analysed using PROC GLM of SAS statistical package. The genotypes 9 environ- ment interactions were significant, therefore the two test locations were considered as ideal environments for genotype comparison. General combining ability effects were significant for B. fusca stem borer resistance and grain yield, suggesting a preponder- ance of the additive gene effects for borer resistance traits. Specific combining ability effects were sig- nificant for B. fusca borer resistance traits and grain yield indicating that non-additive effects were also influential. Based on grain yield heterosis data at Embu, 22 lines were allocated to group A, 18 to group B and 8 to group AB, while at Kakamega, 24 lines were oriented to group A, 13 to group B and 9 to group AB, whilst the remainder could not be classified. Based on the SCA effects, at Embu, 20 lines revealed positive SCA effects with both testers and were considered to be AB-oriented; while 12 and 7 lines were oriented towards A and B, respectively. A similar trend was observed at Kakamega but only one line exhibited positive SCA effects for grain yield with both testers, while the remainder had negative SCA effects. The identified lines and heterotic groups may be used by maize programmes that emphasize stem borer resistance in hybrids.