Transgenic rootstock - mediated protection of grapevine scion by stacked DNA constructs

Xylella fastidiosa (Xf) is the causative agent of Pierce’s Disease (PD). Collectively, a team of researchers (Lindow, Dandekar, Labavitch/Powell and Gilchrist) has identified or constructed and advanced the evaluation of five (Table 1) novel genes (DNA constructs) that, when engineered into grapevines, suppress symptoms of PD by reducing the titer of Xf in the plant, reducing its systemic spread in the plant, or blocking Xf’s ability to trigger PD symptoms. These projects have moved from the proof-of-concept stage in the greenhouse to characterization of PD resistance under field conditions where current data indicate that each of the five transgenes dramatically reduces the disease levels under field conditions. These existing field trials will continue through 2016. Importantly, each of the five DNA constructs, when incorporated into transgenic rootstock, has shown the ability to protect non-transformed scion, with obvious benefit: any of many unmodified varietal scions can be grafted to and be protected by any of a small number of transformed rootstock lines. Under Objective 1, the ability of transgenic rootstock to protect all or most of the scion, even at a distance from the graft union, will be tested. Objective 2 addresses the issue of durability, the capability of genetic resistance to avoid being overcome by evolving virulent versions of the Xf pathogen, a critical factor for a long-lived perennial crop such as grapevine. The approach under Objective 2 is “stacking,” the 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. The proposed changes are the next logical step toward achieving commercialization of transgenic resistance. Stacked transgene rootstock lines will be ready for evaluation in 2015, with results from greenhouse testing by 2016.