Leafminer Resistance in Spinach

Abstract

Leafminer (Liriomyza spp.) is a major insect pest of many important agricultural crops, including spinach (Spinacia oleracea). Genetic variability in leafminer resistance has not been studied for spinach. The purposes of the present experiments were to evaluate differences in leafminer damage among spinach genotypes, to compare results obtained from insect cage and field experiments, and to study the association among different resistant traits. We screened 345 accessions of the U.S. spinach collection for leafminer resistance in an outdoor insect cage and putative resistant genotypes were further tested in the cage and in the field over 2 years. Although no genotype was immune to leafminers, significant genotypic differences were found for leafminer stings per unit leaf area, mines per plant, and mines per 100 g plant weight. PI 274065 had the lowest sting density, whereas PI 174385 showed the fewest mines per unit plant weight among genotypes in the field. Rank order of stings per square centimeter leaf area did not significantly change for the genotypes in the cage and field tests, and the sting results from different tests were also highly correlated, suggesting that a cage test could be used to screen germplasm for fewer leafminer stings, and sting density is a reliable trait for the selection of leafminer feeding nonpreference. Stings per unit leaf area were not correlated with mines per plant or per 100 g plant weight, which suggests that feeding nonpreference does not necessarily mean oviposition–nonpreference for a spinach genotype and these two traits can be improved independently. Stings per square centimeter leaf and mines per 100 g plant weight had little correlation with plant weight in cage and field tests, suggesting that leafminer sting and mine densities are not associated with plant biomass, and it is possible to improve and combine the leafminer resistance and yield traits in a spinach cultivar. From these findings, the genetic improvement of spinach for leafminer resistance seems feasible.