Photosynthetic and glycoalkaloid responses of potato (Solanum tuberosum L.) to Colorado potato beetle (Leptinotarsa decemlineata Say) defoliation

Abstract

Photosynthetic and glycoalkaloid responses of potatoes (Solanum tuberosum L.) to varying levels of Colorado potato beetle (Leptinotarsa decemlineata Say) and manual defoliation were measured on 'Cal Red' and 'Russet Burbank' plants. No alteration in photosynthesis was observed on the remaining tissue of an injured leaf for Cal Red and Russet Burbank leaves defoliated by larval Colorado potato beetles nor for Russet Burbank leaves defoliated by adult Colorado potato beetles. No significant differences were observed between actual Colorado potato beetle and manual defoliation for both varieties. In both of the whole-plant defoliation studies, defoliation level consistently did not result in increased or decreased gas exchange parameters of individual leaves compared to undefoliated controls. There was no evidence of delayed leaf senescence in defoliated treatments. Plants defoliated by Colorado potato beetles had a significantly greater production of glycoalkaloids than in control and in manually defoliated plants for both skin and inner tissue.

There was also a 32.6% and a 36.8% glycoalkaloid increase in skin and inner tissue of tubers from plants defoliated at high levels by Colorado potato beetles in comparison to control plants. Although a significant difference in glycoalkaloid concentration was not observed among the treatments in subsequent experiments, the skin and inner tissue of tubers from plants defoliated at high levels by Colorado potato beetles increased by 18.9% and 12.7% in comparison to tubers from control plants. For the experiments where glycoalkaloid concentrations were measured, there was a significantly greater concentration of glycoalkaloids in the skin versus the inner tissue of potatoes, in addition, for the initial glycoalkaloid experiment, the concentration of tuber extract required to reduce Chinese hamster ovary cellular proliferation by 50% was 10 times less for the skin versus the inner tissue. The dietary risk assessments revealed that the glycoalkaloid concentrations within the inner tissue of tubers from control plants, manually defoliated plants, and high Colorado potato beetle defoliated plants exceeded the toxic endpoint for all human subgroups at less than the 99.9th percentile of exposure.