Effects of Nutrient Supply on Citrus Resistance to Root Herbivory by <I>Diaprepes abbreviatus</I> L. (Coleoptera: Curculionidae)

Abstract

Abstract We treated two citrus cultivars with a complete fertilizer diluted to 25, 100, 200, or 400 ppm N to test whether increasing fertilizer concentration alters root and leaf chemistry and decreases resistance of citrus to root-feeding larvae of Diaprepes abbreviatus L. Roots and leaves of better-nourished ‘sour orange’ (Citrus aurantium L.) had larger amounts of total proteins and increased activities of enzymes associated with resistance than did plants given 25 ppm N. The fertilizer effect was less consistent for ‘Swingle citrumelo’ (C. paradise Macf. × Poncirus trifoliate L.), which has greater resistance to D. abbreviatus. Herbivory increased root protein content and peroxidase but decreased activities of chitinase and β-1,3-glucanase, which are enzymes associated with resistance to microbial pathogens. When significant, the effect of root herbivory on enzyme activities in leaves was opposite the effects on roots. Fertilizer and herbivory rarely interacted, indicating enzyme induction was not a f...