Durable Powdery Mildew Disease Resistance in Vitis Vinifera: Proof-of-Function and Discovery of Genetic Variation

For the past sixty years, mlo resistance to barley powdery mildew has remained durable and is now incorporated into over 50{aed9a53339cdfc54d53cc0c4af03c96668ab007d9c364a7466e3349a91bf0a23} of the European barley acreage. Related mlo genes in Arabidopsis, peach, pea, and tomato have recently been discovered and also confer resistance to powdery mildew via the same penetration resistance mechanism. Previously, we identified four strong candidates for mlo resistance in grapevine. To determine whether this gene could confer durable resistance in grapevine, we are pursuing a transgenic gene silencing approach. In 2009, we designed, cloned and confirmed 17 new artificial microRNA (amiRNA) silencing constructs. In 2010, we initiated a collaboration with Dr. Bruce Reisch to develop stably transformed Chardonnay grapevines. Plans are to silence four VvMlo candidate resistance genes individually, in pairs, and all at once in a thorough effort to confirm resistance gene function. In addition, we implemented a similar strategy to silence two candidates for a second resistance gene from Arabidopsis, Pmr6, individually and in pairs. Typical results for biolistic transformation experiments yielded hundreds of transiently-transformed Chardonnay cells per Petri dish. To-date we have regenerated a total of 58 transgenic plants that are ready for functional characterization and have over 600 total embryos after selection that may germinate for transfer to plant growth medium. While the transgenic assays described above could efficiently result in the development of transgenic V. vinifera cultivars with powdery mildew resistance, the information obtained could also be harnessed to identify V. vinifera breeding germplasm with previously undetected resistance alleles.