Grant SA 7627 . PIERCE ’ S DISEASE CONTROL AND BACTERIAL POPULATION DYNAMICS IN WINEGRAPE VARIETIES GRAFTED TO ROOTSTOCKS EXPRESSING ANTI - APOPTOTIC SEQUENCES

Two DNA sequences (VvPR1 and UT456) were selected by a functional screen to test for ability to suppress the Programmed Cell Death-dependent symptoms of PD. Greenhouse experiments confirmed that these two different anti-PCD DNA sequences prevented PD symptoms in the PD-susceptible cultivar Thompson Seedless and the commercial rootstock Freedom. Furthermore, the bacterial titer in the transgenic plants was reduced four to six orders of magnitude below that reached in untransformed control vines. In contrast, all untransformed control plants died within 3-4 months after inoculation while the transgenic plants were asymptomatic for 12 months. The net effect of these transgenes is to limit bacterial titer but not distribution of bacteria in the asymptomatic plants. From the perspective of the grape-bacterial interaction, it appears that the anti-PCD genes suppress PD symptoms and functionally confine (Xf) to an endophytic ecology in the xylem equivalent to that seen in the related asymptomatic host Vitis californica. Clonal copies of the transgenic and control plants were moved to two field locations under an APHIS permit secured by PIPRA and were inoculated July 21, 2011. Greenhouse data obtained from grafting experiments indicate the protective effect of these genes may be transferred across a graft union to protect a susceptible untransformed scion. Grafted plants expressing VvPR1 and UT456 in the rootstock, but not the scion, have been moved to the field site for inoculation in the spring of 2012.