Methods to manage uncontrolled flow of transgenes via pollen and seeds are increasing in importance as transgenic crops become more commonplace. In many parts of the world, grapevine scions are grafted onto rootstocks, which are adapted to resist adverse soil conditions and pests and/or to promote vigor. Water, minerals and other important nutrients are transferred in bulk from the rootstock to scion via the xylem. Thus, it is possible that bioactive peptides produced by a transgenic rootstock and deposited into its xylem sap would be similarly transferred to a non-transgenic scion. If the peptide conferred a desirable trait to the non-transgenic scion, such as disease resistance, the issue of unwanted gene flow would be solved, since transgenic pollen and seeds would not be produced during flowering and fruit production. Furthermore, the commercialization of transgenic grapevines would be simplified, since relatively few transgenic rootstock varieties would be needed to protect any non-transgenic scion. As an example, transgenic rootstock technology might be used in the control of Pierce's disease (PD), which is caused by the xylem-limited bacteria, Xylella fastidiosa. Antimicrobial peptides produced by a transgenic rootstock may control bacteria in the xylem sap of a non-transgenic scion, thus providing PD resistance. To test this hypothesis, transgenic Vitis vinifera 'Thompson Seedless' expressing the Shiva-1 lytic peptide gene was treated as a rootstock. Non-transgenic V. vinifera 'Cabernet Sauvignon' and 'Thompson Seedless' were grafted onto the rootstock. Controls consisted of grafted and non-grafted transgenic and non-transgenic vines. Presence of the Shiva-1 peptide in xylem sap of the scion was detected by EnzymeLinked Immunoabsorbent Assay (ELISA).