DIALLEL ANALYSIS OF RESISTANCE TO THE SPOTTED STEM-BORER (CHILO-PARTELLUS SWINHOE) IN MAIZE

The spotted stem-borer (Chilo partellus Swinhoe) causes heavy yield losses in maize. Only a few of the exotic maize genotypes have been identified as resistant in evaluations carried out at the ICIPE. The objective of this study was to obtain information on patterns of combining ability of resistance to the spotted stem-borer to maximize their use in resistance breeding programme. A ten-parent diallel analysis was used to evaluate the potential for genetic improvement. Parental genotypes (resistant MP701. MP702, MP704, ICZ1-CM and ICZ2-CM: susceptible Poza Rica 7832, V37, OH43, Inbred G and Inbred A) and their F1s (excluding reciprocals) were grown in the field and artificially infested with Chilo partellus eggs. The combining ability analysis for leaf feeding, deadheart, stem-tunnelling and number of entry/exit holes indicated significance of both general and specific combining ability effects. The GCA/SCA variance ratio confirmed that additive component was the most important factor in the inheritance of resistance to leaf feeding. For deadhearts both additive and non-additive effects were equally important. The parent MP704 was found to be the best general combiner followed by MP702, MP701 and ICZ2-CM. The F1 hybrids involving resistant with resistant and in a few cases resistant with susceptible showed significant specific combining ability effects for resistance. The highly significant correlation coefficients between parents and GCA estimates suggested that initial selection of parents for hybrid combinations may be largely based on insect reaction of parents.