Mechanisms and genetic diversity for host plant resistance to spotted stem borer, Chilo partellus in sorghum, Sorghum bicolor

Levels of resistance to spotted stem borer, Chilo partellus, in the germplasm are low to moderate and therefore we evaluated 25 sorghum genotypes for resistance to stem borer to identify lines with diverse mechanisms of resistance to this insect. Leaf glossiness was significantly and negatively associated with low deadheart formation. Dwarf genotypes with fewer nodes showed more deadheart formation. Antixenosis and/or antibiosis for leaf feeding, and reduced deadheart formation, tunnelling, and number of exit holes resulted in lower losses owing to C. partellus damage. Axillary tillers compensated for loss in grain yield owing to borer infestation as a result of deadheart formation, but their synchrony for maturity with the main plant is quite important. Path coefficient analysis revealed that direct effects of stem tunnelling on loss in grain yield were greater than leaf feeding and deadhearts. However, leaf feeding via stem tunnelling showed maximum indirect effects on loss in grain yield. Estimates for broad-sense heritability and genetic advance suggested that it is possible to improve for grain yield under stem borer infestation. Heritability estimates for grain yield were usually higher than for stem borer damage parameters. Multi-trait cluster analysis placed the test genotypes into four and five clusters in rainy and post-rainy seasons, respectively. The genotypes placed in different groups, and showing resistance to leaf feeding, deadheart formation, stem tunnelling, and/or compensation in grain yield can be used for sorghum improvement