METABOLIC CHANGES IN BARLEY SEEDLINGS AT DIFFERENT APHID INFESTATION LEVELS

Different infestation levels with the greenbug (Schizaphis graminum Ro ndani) were correlated with physiological parameters and several metab olite concentrations in young barley plants (Hordeum vulgare cv Aramir ). Leaf water potential, chlorophyll content, carbon dioxide assimilat ion and total soluble carbohydrates decreased significantly with more than 18 aphids per plant. Conversely, proline concentration increased with more than 18 aphids. With 100 individuals per plant, sugar concen trations decreased five times with respect to the non-infested control . Similar changes were observed in plants subjected to drought stress. These results suggest that several metabolic changes that occur in ba rley infested by a large number of aphids may be due in part to the lo wer leaf water potential caused by the insect.