Mechanisms of Sorghum resistance to the spotted stalkborer, Chilo partellus (Swinhoe) (Lepidoptera: Pyralidae)

Abstract

The spotted stalkborer Chilo partellus is one of the most notorious pests in Kenya of cereal crops especially maize and sorghum particularly in semi-arid areas. These studies showed that ovipositing maize stalkborers have distinct preferences for certain sorghum cultivars. Cultivar IS 2205 was the least preferred while IS 18363 was the most preferred. Experiments to identify the factors responsible were inconclusive. Evidence pointed to both biochemical and biophysical factors. First instar larval establishment studies were also inconclusive even though it was demonstrated that larval establishment was different among the cultivars used. The only definite evidence for poor establishment in some cultivars was biophysical. Different cultivars were significantly different in their susceptibility to leaf damage. The tendency to form deadhearts was also significantly different. Cultivars were not significantly different in their susceptibility to tunnelling even though they had different amounts of fibre, lignin and sucrose. The single most important factor for the different cultivar susceptibilities was in their different tolerance to C. partellus attack. Tillering, in particular, was demonstrated to play an important role in compensation for damage. The ability to flower and to produce seed in spite to having a high infestation of stalkborers were also very significant. Susceptible cultivars dried up before they had flowered. Others still flowered but could not form seed. Using tolerance as a criterion for resistance showed IS 18520 to be the most resistant. Formation of multiple heads was also shown to be an important factor as a result of stalkborer infestation. Different cultivars had varying effects on the development of C. partellus (antibiosis). However, the antibiotic effect was either insignificant or only just significant statistically. The use of the resistant crop varieties to insect pests is one of the best and environmentally sound methods in pest management