Abstract: Grapevine（Vitis vinifera L.）incurs significant yield and quality losses from powdery mildew（Erysiphe necator Schw.）. Here，we used the CRISPR/Cas9 system to precisely edit the susceptibility gene VviEDR2（Enhanced disease resistance 2）and provide reference for disease resistance breeding. We designed a target site in DUF1336 domain of the VviEDR2 gene for the CRISPR/Cas9 vector，and obtained transgenic plants via Agrobacterium-mediated transformation，using somatic embryos of the Thompson Seedless cultivar. Sequencing revealed that 8 out of 25 transgenic plants carried different type of biallelic mutations in target sites and the editing efficiency is 32%. These mutants exhibited reduced growth compared to wild type，such as smaller leaves，thinner and fasciculate stems. Inoculation assays with an adapted grapevine powdery mildew isolate En NAFU1 showed that hyphal growth is significantly restricted on mutant grapevine leaves with obvious H2O2 accumulation in penetrated epidermal cells at 5 days post inoculation. Conversely，massive hyphae and haustoria，but no obvious accumulation of H2O2，were observed in the leaves of wild type. These results indicated that CRISPR/Cas9 technology could be utilized to knockout susceptibility gene VviEDR2 in grapevine，which could improve powdery mildew resistance.

Key words: grapevine, CRISPR/Cas9, gene editing, VviEDR2, Erysiphe necator