Effect of potassium nitrate on gramine content and resistance of barley against the aphid Schizaphis graminum

Abstract

Barley seedlings grown at different levels of KNO3 were infested with aphids. The infestation levels reached were inversely proportional to KNO3 supply. The population growth rate of the greenbug Schizaphis graminum decreased in seedlings watered with nutrient solutions containing 30 mM or more nitrate. Nitrate accumulated more in the first leaf than in the second of these seedlings as a function of nitrate fertilization. The concentration of the indole alkaloid gramine, an insect resistance factor in barley, increased in the second leaf (youngest), and decreased in the first one (oldest) with increasing NO3− in the nutrient solution. The feeding behaviour of aphids was negatively affected by KNO3 in artificial diets and in the plants. It is suggested that nitrate fertilization may affect aphid performance on barley seedlings because it causes changes in gramine concentration in the leaves.