Harnessing native genetic variation for resistance to field and storage insects pests in tropical maize

Abstract

The stem borer ( Chilo partellus Swinhoe) causes 12%–17% yield losses in the field, while additional 15%–30% grain losses are caused by the maize weevil ( Sitophilus zeamais Motschulsky) in storage across sub-Saharan Africa. Despite advances in host plant resistance, maize hybrids with combined resistance to both insects remain unknown. The objective of this study was to combine resistance to stem borer and maize weevil in elite maize germplasm through breeding. Forty maize inbred lines were divided into groups of five lines based on insect resistance levels. Eight sets of 25 hybrids each were generated using a 5 x 5 North Carolina II mating design within each set. The resulting 190 F 1 hybrids with sufficient seeds were evaluated for grain yield and stem borer damage across four environments in Kenya. Resistance to Chilo partellus was assessed under field conditions, while post-harvest grain was screened for Sitophilus zeamais resistance under controlled laboratory conditions. The results showed significant differences ( p ≤ 0.05) among hybrids for grain yield and insect resistance parameters such as leaf damage, grain weight loss and undamaged kernels. General combining ability effects associated with both male and female parents were highly significant ( p ≤ 0.01) for all traits indicating involvement of additive gene effects. Specific combining ability (SCA) effects were significant for grain yield under protected and insect infested conditions, and undamaged kernels indicating the role of non-additive gene effects for these traits. However, the SCA effects were not significant for leaf damage and grain weight loss suggesting that non-additive gene effects did not play a major role for these traits. These findings imply that heterosis can be exploited to improve hybrids for grain yield under both insect infested and protected conditions. Approximately 8% of the hybrids exhibited resistance to stem borer, while several showed reduced grain weight losses due to maize weevil damage. Grain yield advantage (standard heterosis) ranged from 26% to 41% over commercial check hybrids, indicating that breeding for combined resistance has potential for improving both yield and insect resistance. Four hybrids (17 x 40, 19 x 40, 3 x 25, 2 x 23) combined dual resistance with superior grain yield demonstrating feasibility of developing resilient maize varieties.