Abstract:

This study evaluated sweet potato resistance to sweet potato weevils (Cylas spp.) and investigated the phytochemicals that mediated this defence. New Kawogo, LIR302 and ARA228 were shown to be the most resistant based on stem and root damage. Significant differences were observed on the number of faecal droppings, feeding holes and eggs laid on the root in a choice and no-choice bioassays confirming that New Kawogo, LIR302 and ARA228 affected development and emergence of adult weevils. hexadecyl caffeic, six hydroxycinnamic acid esters, including hexadecyl coumaric, octadecyl caffeic, octadecylcoumaric, heptadecylcaffeic and 5-O-caffeoylquinic acid esters were identified on the root surface and amounts of these differed significantly between resistant and susceptible varieties. The mean number of C. punctilios and C. brunneus feeding holes, faecal droppings and egg laid on the root core were significantly different among the root cores treated with synthetic hydroxycinnamic acid esters. The study also showed that there were significant differences in the root volatiles of resistant and susceptible variety both before and after infestation. The larval survival of sweet potato weevil was significantly affected by hydroxycinnamic acid esters treatment and Bt-toxin applied on the diet. There were also significant differences in percentage sweet potato weevil root infestation among genotypes of the segregating population. The genotype by environment (GxE) interaction effect was also significant on the sweet potato weevil damage on the stem portion of the sweet potato vine indicating that weevil stem damage is dependent on the season. The mean number of sweet potato weevil feeding holes differed significantly on the root of the genotypes of the segregating population in the feeding and oviposition bioassay. There was significant difference in total hydroxycinnamic acid (HCA) esters among the genotypes of the segregating population. The distribution of genotype mean total HCA ester concentration was skewed to the left and only one progeny, NKB257, had higher total HCA ester concentration than New Kawogo, the resistant mother used in the crossing. A weak but significant correlation between total HCA ester concentration and sweet potato weevil root damage was observed signifying that resistance to sweet potato weevils depended on other factors as well. The results are discussed in terms of how they might be incorporated into integrated pest management of sweet potato weevils.