Abstract:

This study evaluated sweetpotato 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
Six hydroxycinnamic acid esters, including
hexadecylcaffeic, hexadecylcoumaric, octadecylcaffeic, 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. puncticollis 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
sweetpotato weevil was significantly affected by hydroxycinnamic acid esters
treatment and Bt-toxin applied on the diet. There was also significant differences in
percentage sweetpotato weevil root infestation among genotypes of the segregating
population. The genotype by environment (GxE) interaction effect was also
significant on the sweetpotato weevil damage on the stem portion of the
sweetpotato vine indicating that weevil stem damage is dependent on the season.
The mean number of sweetpotato weevil feeding holes differed significantly on the
root of the genotypes of the segregating population in the feeding and oviposition
v
emergence of adult weevils. 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 sweetpotato weevil root damage was observed
signifying that resistance to sweetpotato weevils depended on other factors as well.
The results are discussed in terms of how they might be incorporated into integrated
pest management of sweetpotato weevils.