Leptine Glycoalkaloids Reduce Feeding by Colorado Potato Beetle in Diploid Solanum sp. Hybrids

Abstract

Leptine glycoalkaloids in leaves of the weedy diploid potato, Solanum chacoense Bitt., have been shown to reduce feeding by Colorado potato beetle (CPB; Leptinotarsa decemlineata Say). Development of cultivated potatoes with natural resistance to CPB has the potential to reduce costs and environmental impacts of production by reducing pesticide use. Through efforts to move the genes controlling leptine biosynthesis into cultivated potato, a series of hybrids was generated between the high leptine producing S. chacoense and a cultivated type, S. phureja Juz. and Buk. These hybrids were evaluated for solanine (+chaconine), leptinins, leptines, and total steroidal glycoalkaloid content. All hybrids contained leptines, but at different levels (ranging from 117 to 802 mg·g-1 dry weight of leptine aglycon). Some hybrids appeared to convert solanine (+chaconine) to leptinine and leptine efficiently and had no detectable solanine in sampled leaves. To verify the biological significance of these glycoalkaloids, leaf tissue was subjected to feeding assays with second instar CPB. CPB feeding rate ranged from 38 to 87 mm2·d-1 and was most closely correlated with leptine concentration. A minimum leptine level of 300 mg/100 g fresh leaves suppressed feeding by 50%, and levels below this had no effect on CPB feeding.