Genetics of host plant resistance in food crops with special reference to sorghum stem-borers

Abstract

A genetic analysis of the resistance of sorghum to stem-borers was carried out in the field in Kenya in 1981-82 using a 6 X 6 diallele cross. F1 hybrids did not differ significantly from mid-parental values, suggesting intermediate inheritance. However, resistance was partially dominant to susceptibility. Combining ability analysis showed that resistance to primary damage (percentage dead-hearts) was governed by both additive and non-additive types of gene action, while secondary damage (percentage stem-tunnelling) was governed predominantly by additive gene action. It was noted that the inheritance patterns of primary and secondary damage were different. Tunnel length showed a positive correlation with the number of larvae per plant and negative association with plant height, but had no correlation with grain yield per plant. On the basis of larvae recovered from the tunnelled plants, Chilo partellus (Swinh.) was found to be the predominant stem-borer species, followed by Sesamia calamistis Hmps., Eldana saccharina Wlk. and Busseola fusca (Fuller). The importance of genetic studies of host-plant resistance in deciding breeding strategies for insect resistance is discussed.ADDITIONAL ABSTRACT:Genetic analysis of the resistance of sorghum to stem borers was carried out on data from a 6 X 6 diallel cross. F1-hybrid values did not differ significantly from midparental values, suggesting intermediate inheritance. However, resistance was partially dominant to susceptibility. Combining ability analysis showed that resistance to primary damage (percentage dead hearts) was governed by both additive and nonadditive gene action, while secondary damage (percentage stem tunnelling) was governed predominantly by additive gene action. Inheritance patterns of primary and secondary damage were different. Tunnel length showed a positive correlation with the number of larvae per plant and negative association with plant height. On the basis of larvae recovered from the tunnelled plants, Chilo partellus was the predominant stem-borer species, followed by Sesamia calamistis, Eldana saccharina and Busseola fusca