Transgenic Rootstock-Mediated Protection of Grapevine Scion by Introduced Single and Dual Stacked DNA Constructs Principal Investigator

INTRODUCTION Collectively, a team of researchers (Lindow, Dandekar, and Gilchrist) identified, constructed and advanced to field evaluation five novel DNA constructs (Table 1) that, when engineered into grapevines, suppress symptoms of Pierce’s Disease (PD) by a) reducing the titer of Xylella fastidiosa (Xf) in the plant, b) reducing systemic spread of the bacteria or c) blocking Xf’s ability t o trigger PD symptoms. Each of the five transgenes, when expressed as single genes, reduced the disease levels under field conditions both as full plant transgenics and in transgenic rootstocks grafted to a nontransformed PD susceptible scion. The continuation of the basic research and the field trials to be described herein results from the field data indicating that several of the five DNA constructs, when incorporated into transgenic rootstock, have shown potential for protection of a non-transformed scion across a graft union. The present field trial consisting of single gene constructs will be discontinued at the end of the 2016 growing season to be replaced w i t h a second field trial designed to evaluate rootstocks bearing paired combinations of the five constructs. If successful, the obvious benefit would be that any unmodified (non-transgenic) varietal wine grape scion could be grafted to and be protected by transformed rootstock lines. This approach involves “stacking,” a combination of distinct protective transgenes in a single rootstock line, which is intended to foster not only durability but also more robust protection of the non-transformed scion against PD. Stacked transgene rootstock lines are now being received for greenhouse whole plant PD evaluation, then grafting and PD evaluation, first under controlled greenhouse conditions and then to produce ramets of the most suppressive transgenic rootstock lines for field evaluation beginning in 2017.