The effect of phylloxera biotype and water stress on phylloxera resistance in grape rootstocks

Two experiments were conducted to determine whether water stress affected rootstock resistance to phylloxera, Daktulosphaira vitifoliae, biotype A and phylloxera biotype B.; An Oakville, Napa Valley, California experiment tested fruiting cultivar Vitis vinifera cv. Cabernet Sauvignon with two water stress levels (high stress and low stress), two rootstock cultivars (V. rupestris cv. St. George and V. vinifera X V. rupestris cv. AxR#1) and three phylloxera treatments (control, no interplanted vine and no phylloxera; interplanted vine and no phylloxera; biotype A phylloxerated, interplanted vine). Fruit chemistry, fruit yield and vegetative growth measures were used to determine vine performance. Data were collected for the 1989, 1990 and 1991 seasons. Water stress significantly decreased vine performance but did not alter rootstock resistance to phylloxera. The St. George and AxR#1 vines retained resistance to biotype A even when under water stress. The survival of non-phylloxerated, interplanted vines indicated that the spread of phylloxera biotype A was very slow. A potted vine experiment tested fruiting cultivar Cabernet Sauvignon on rootstock cultivar AxR#1 grown in containers with two water stress treatments (no stress and stress) and three phylloxera treatments (control, no phylloxera; phylloxera biotype A; and phylloxera biotype B). Fruit chemistry, fruit yield and vegetative growth measures were used to determine vine performance. Data were collected for the 1990 and 1991 seasons. Water stress treatments caused a significant decrease in vegetative growth. Vines with phylloxera biotype A and control treatments did not differ from each other. The phylloxera biotype B treatment produced significantly lower pruning weights and significantly less shoot length. Water stress did not affect the phylloxera resistance of the rootstock.; In both experiments, water stress reduced vine growth but had no effect of the phylloxera resistance of either of the rootstocks in the trials.