Host range evaluation of Verticillium nonalfalfae isolate Vert56 used for biological control of Ailanthus altissima : grapevine cultivars exhibit resistance

The biological control of the highly invasive Tree of Heaven (Ailanthus altissima) with the vascular wilt fungus Verticillium nonalfalfae isolate Vert56 has proven to be highly effective, with no known adverse effects on non-target tree species so far. Based on isolate Vert56, a commercial product was developed and is currently marketed under emergency authorisations for specific indications. Due to the increasing invasion of vineyards by A. altissima, demand for the application of isolate Vert56 in viticulture has risen. As common grapevine Vitis vinifera subsp. vinifera is considered susceptible to some Verticillium species, a field inoculation trial was conducted to test the susceptibility of the twelve frequently grown grapevine cultivars to V. nonalfalfae isolate Vert56. The vines were inoculated twice and assessed over three consecutive growing seasons, starting on the date of the first inoculation. In addition, re-isolation and molecular genetic detection of V. nonalfalfae were attempted. Ailanthus growing on site was inoculated in parallel and displayed high disease intensity, as it has been shown in previous studies. In contrast, no symptoms of Verticillium wilt were observed on any plant of the tested grapevine cultivars; in fact, all treated plants developed similarly to those of the control groups. The pathogen was detected only in a single grapevine plant shortly after inoculation. Based on these results, we conclude that grapevine is resistant to V. nonalfalfae isolate Vert56 and that application of this biological control method in viticulture is safe and suitable, in order to combat highly invasive A. altissima.