Testing for glycoalkaloids

Summary

INTRODUCTION

Glycoalkaloids are a group of toxic compounds found in potatoes. They are present at high concentrations in the leaves and shoots of potato plants and in tubers which have been exposed to light. Fortunately in the normal tubers of current popular varieties the level of glycoalkaloid is quite low (Parnell et al. 1984). It is thought that the function of glycoalkaloids might be related to disease and pest resistance.

Although the level of glycoalkaloids in popular varieties is low, there is a danger that modern breeding techniques may result in elevated levels in newly-bred varieties. The reason for this stems from the practice of introducing disease resistance characters from wild plants or primitive cultivars. For example, a variety of potato bred for resistance to Colorado beetle (Leptinotarsa decemlineata) showed unacceptably high levels of glycoalkaloid in the tubers (Sinden & Webb 1974).

Glycoalkaloid level is expressed as milligrams per 100g fresh tuber. Potatoes with less than 20mg/100g are considered entirely acceptable, potatoes with more than 20mg/100g often have a bitter, metallic taste and potatoes containing 50-100mg have caused severe illness.

Trials have consistently shown significant varietal influence on glycoalkaloid content. In view of this and the toxicity effects it is felt that glycoalkaloid screening is of considerable importance.

METHODOLOGY

At the National Institute of Agricultural Botany all National List candidate varieties of potato are screened for glycoalkaloid content. Samples from each of three sites are analysed in triplicate.