Establishment of a picloram-induced somatic embryogenesis system in Vitis vinifera cv. chardonnay and genetic transformation of a stilbene synthase gene from wild-growing Vitis species

To facilitate genetic improvement, an efficient system of embryogenic culture induction, maintenance and transformation in Vitis vinifera cv. Chardonnay was developed using picloram. Whole flowers produced the most embryogenic calluses on induction media containing Murashige and Skoog's (MS) basal salts and 3.0 mg L-1 picloram with different concentrations of 2,4-dichlorophenoxyacetic acid and 6-benzyladenine. Proembryonic masses (PEM) cultured on maintenance and proliferation media (MPM) containing MS basal salts and picloram had the highest proliferation efficiency within 2 months. Additionally, the best PEM formation was found with MPM containing MS basal salts and 2.0 mg L-1 picloram. Then this PEM cultured on MPM were transferred to embryo germination medium containing MS basal salts, 0.2 mg L-1 kinetin and 0.1 mg L-1 2-naphthoxyacetic acid, the optimal medium for normal plantlets regeneration. A single copy of the stilbene synthase gene VpSTSgDNA2 from Chinese wild Vitis pseudoreticulata was transferred into regenerated Chardonnay via Agrobacterium tumefaciens-mediated transformation and confirmed by Southern blot analysis. The positive transgenic grapevine lines exhibited higher levels of stilbene and H2O2 than wild-type vines and could slightly reduced the growth of powdery mildew.