Physiological Effects of Galls Induced by Phylloxera notabilis (Homoptera: Phylloxeridae) on Pecan Foliage

Abstract

Effect of the Phylloxera notabilis Pergande gall was assessed on leaf chlorophyll, leaf nutrient status, and leaf gas exchange of nursery pecan, Carya illinoensis (Wangenh.) C. Koch, ‘Stuart’. Gall tissue was significantly different from ungalled tissue in every nutrient investigated. Galls contained 60% N, 50% Ca, and 50% Al, but 260% K, 150% P, and 200% Na of leaf tissue from uninfested (control) leaflets. Analysis of concentric rings of tissue revealed that chlorophyll and all macronutrients except P were altered in leaf tissue 0–1.5 cm away from a gall compared with control leaflets. Net CO2 assimilation rate of infested tissue was reduced by an average of 27%, which was equivalent to almost 4-fold the percentage of gall area occurring in the field of measurement. Significant reductions in leaf conductance and transpiration also occurred over leaf tissue containing a gall. Cumulative gall cross-sectional area was negatively correlated with net CO2 assimilation rate. Thus, not only did the P. notabilis gall divert resources away from normal metabolic function, but it also interfered with the nutrient status and photosynthetic capacity of adjacent leaf tissue.