Histological Study of Leaf Galls Induced by Phylloxera in Vitis (Vitaceae) Leaves

The galls induced by hemipterans generally show hypertrophy of the phloem; these insects usually feed on the sap in the sieve tube elements, occasioning phloem bundle hypertrophy. However, there are some exceptions; for example, the phylloxerids feed on the gall wall parenchyma. It has remained unknown, however, whether Daktulosphaira vitifoliae (the vine phylloxera) also causes hypertrophy of the phloem bundles. The galls induced by D. vitifoliae in leaves of the rootstock variety Richter-110 (Vitis berlandieri × Vitis rupestris) were examined microscopically. D. vitifoliae was found capable of inducing vascular bundle hypertrophy, as well as the nutritional enrichment of the gall wall parenchyma cells upon which the insect feeds. The hypertrophy of the phloem bundles commonly seen in hemipteran-induced leaf galls also occurs in those induced by D. vitifoliae, even though these do not feed on the phloem contents, but rather on the gall wall parenchyma. The appearance of phloem bundle hypertrophy in hemipteran-induced leaf galls requires the remobilization of photoassimilates that might affect the productivity of the affected plant.