Susceptibility of Vitis vinifera L. cv. Redglobe and Thompson Seedless to Pierce's disease
The susceptibility of two grapevine (Vitis vinifera L.) cultivars, Redglobe and Thompson Seedless, to Xylella fastidiosa Wells et al. infection and Pierce's disease (PD) was evaluated by monitoring the rate of systemic bacterial movement in plants. Rooted cuttings of the two cultivars were pruned to two shoots and one shoot was needle-inoculated with X. fastidiosa to monitor movement of bacteria into the noninoculated shoot. In the first experiment, at 6-, 12-, and 18-week postinoculation, X. fastidiosa was detected in significantly more noninoculated shoots of Redglobe plants than Thompson Seedless plants. In the second experiment, bacteria from source plants of each cultivar were inoculated into each cultivar to test if the source of bacteria affected infection. There were no differences in detection of X. fastidiosa from either source cultivar in either shoot of the two cultivars. However, Redglobe plants had significantly lower survivorship. At 30-wk postinoculation, only 2 to 7% of Redglobe plants were alive compared with 51% of Thompson Seedless plants. Additionally, at 26-wk postinoculation, four of the nine surviving Redglobe plants had new shoot growth and 43 of the 50 surviving Thompson Seedless plants had new shoot growth. At 29-wk postinoculation, ELISA of this new growth detected surviving infections in all Redglobe plants, but in only 82% of Thompson Seedless plants. Overall, Redglobe plants were more susceptible to PD infection and subsequent development of disease leading to plant death than Thompson Seedless plants.