Evaluation of Selection Methods for Resistance to a Specialist Insect Pest of Squash (Cucurbita pepo)

Abstract

Plant varieties resistant to insect pests are a critical component of integrated pest management, but challenges associated with plant breeding for insect resistance, such as a long breeding cycle duration and low trait heritability, slow progress in the field. In this study, we tested two novel selection schemes to improve genetic gain for resistance to the major pest, the striped cucumber beetle (Acalymma vittatum), in squash (Cucurbita pepo, e.g., zucchini). First, we tested an indirect selection scheme using a proxy insect with correlated resistance phenotypes, Trichoplusia ni, in place of the seasonally available A. vittatum. We found that while resistance to herbivory by T. ni was heritable, there was no reciprocal benefit for resistance to A. vittatum. Second, we tested genomic selection, a method that allows for selection without phenotyping every generation, for both resistance to A. vittatum directly and resistance to the proxy T. ni. Although there was moderate genomic predictive ability, we did not observe realized gains from selection in field trials. Overall, strategies that minimize investment in direct phenotyping, leverage efficiencies from phenotyping correlated traits, and shorten breeding cycle duration are needed to develop insect resistant varieties, and this study provides examples and empirical data of two such approaches deployed in an applied breeding program.