Screening of South African sugarcane cultivars for resistance to the stalk borer, Eldana saccharina Walker (Lepidoptera: Pyralidae)

Resistant sugarcane cultivars are an important control measure for the stalk borer, Eldana saccharina Walker, in South African sugarcane, Saccharum spp. hybrids. Selection for resistance is based on field assessments and potted sugarcane screening trials of test cultivars. This paper describes the screening methodology and examines its efficacy for evaluating susceptibility to E. saccharina. Aims were to improve discrimination of borer susceptibility and to develop a quantitative, statistically meaningful method of rating cultivars. Test cultivars were planted in a replicated lattice design and artificially infested with E. saccharina. Four variables, namely length of stalk bored, number of internodes bored, numbers of surviving larvae+pupae, mass of larvae+pupae, that quantified borer damage and performance, were used to calculate a susceptibility/resistance rating for all cultivars on a 'one to nine' unit scale, where two units was equivalent to a 95 % confidence interval and the mid-point of the scale represented the control mean. Ratings were standardized and independent of those of other test cultivars within the same trial. Differences in susceptibility were significant in all trials and well discriminated in the majority. Improved discrimination produced a greater spread of cultivar ratings across the rating scale, facilitating the identification of resistant cultivars. The screening method and variables measured take into account the known resistant mechanisms to E. saccharina and provide a means of estimating the likely impact of cultivars on area-wide pest management in terms of larval survival and moth production.