Natural distribution of Verticillium wilt on invasive Ailanthus altissima in eastern Austria and its potential for biocontrol

Ailanthus altissima is a highly invasive tree species that has become established in warmer climatic zones of Europe. Verticillium wilt shows promise for biocontrol of this invasive tree species. In this study, we conducted a survey on the natural distribution of Verticillium species on A.altissima in eastern Austria. Results of a survey, across the range of A.altissima in Austria, indicated a widespread distribution of V.dahliae (56 of 77 sampled sites) and a rare occurrence of V.nonalfalfae (two of 77 sites). All sites positive for Verticillium spp. were situated at 130m to 240m above sea level. In addition, pathogenicity and virulence of an Austrian isolate of V.nonalfalfae, which is considered the most effective Verticillium species as biocontrol agent against A.altissima, were tested in field inoculations studies. Results revealed that disease progression on A.altissima is negatively influenced by high temperatures in summer. Therefore, inoculation in spring turned out to be the most effective to combat A.altissima. However, due to the common occurrence of V.dahliae in Austria, this pathogen might be considered as alternative biocontrol agent of A.altissima on sites in warmer climates. For that purpose, further investigations of the host range and non-target effects of selected V.dahliae strains should be carried out.