Early subcellular responses of susceptible and resistant Vitis taxa to feeding by grape phylloxera Daktulosphaira vitifoliae

Species, varieties, and hybrids of Vitis are differently susceptible to feeding by the aphid Daktulosphaira vitifoliae (Fitch) (Hemiptera: Phylloxeridae). The differinglevels of susceptibility were examined in Vitis riparia x V. rupestris cv. C-3309, V. vinifera x V. labrusca cv. Weisse Amerikaner, and V. vinifera cv. PortugieserWeissherbst by characterizing early subcellular changes to aphid feeding. We examined the fifth and sixth layers of mesophyll parenchyma between 3 and 48 h after introducing neonate nymphs of D. vitifoliae on to those leaves. In the susceptible variety C-3309, activated and metaplasied cells appeared in 3'6 h of feeding by D. vitifoliae and developed into nutritive tissue in the next 24'48 h. On the contrary, cells of the resistant variety Portugieser Weissherbst accumulated phenolic materials indicating a hypersensitive response; those of Weisse Amerikaner showed a mixed response of developing a nutritive tissue and a concurrent accumulation of phenolic materials especially in cells away from the nutritive tissue, indicating that this hybrid could tolerate D. vitifoliae. Galls developed on the leaves of C-3309 in 21 days, whereas no gall development occurred on the leaves of Portugieser Weissherbst and Weisse Amerikaner. D. vitifoliae nymphs introduced on the leaves of Portugieser Weissherbst died in 3'4 days, whereas on the leaves of Weisse Amerikaner, nymphs lived up to 21 days. Thus early subcellular changes in leaf tissues determined the feeding activity ofnymphs on leaves and the susceptibility of plants to insect feeding.