Expression of Anti-Microbial Genes in Transgenic Grapevines for Enhanced Disease Resistance

Grapevines are susceptible to numerous diseases harming both plants and profits. Transgenic grapevines that resist disease could provide improved disease control as well as economic benefits from the reduction in spray applications. Our overall goal has been to research and develop methods to create transgenic selections of elite cultivars with improved resistance to diseases. The transgenic strategy is especially appropriate for clonally-propagated crops, such as grapevines, where the grape industry is rooted in traditional European grapes with very high disease susceptibility. Eight different antimicrobial peptides (AMPs), which are small proteins known to be inhibitory to a range of bacteria and fungi, were tested to determine which might best provide resistance to bunch rot (Botrytis) and crown gall (Agrobacterium vitis). Two of these peptides, cecropin B and MSI-99, were most promising for controlling growth of A. vitis. A test was run to determine the effect of a combination of these two peptides on A. vitis growth, and their activity was additive. Cecropin B and Shiva 1 were tested against Botrytis cinerea, and were found to be no more effective than either PGL or ESF-39, which had been tested last year. The same eight AMPs were also tested for their effects on germination of powdery mildew conidia. These assays were technically difficult to carry out, but it was clear that none of the tested peptides were highly inhibitory to conidia germination. Some AMPs (e.g. ESF-39 and MSI-99) decreased conidia germination by approx. 50%at 10 µM and higher concentrations. Based on the results from peptide screening, new gene constructs for use in transformation were developed. Two constructs included MSI-99 and cecropin B downstream of a constitutive promoter, while the other two constructs placed these same genes downstream of wound- or pathogen-inducible promoters. Transformation of ‘Chardonnay’ is underway in order to test the potential of these constructs for the improvement of disease resistance.