Non-target effects of Verticillium nonalfalfae isolate Vert56 used for biological control of Ailanthus altissima on agricultural crops known to be generally susceptible to Verticillium spp.

Abstract

Tree of Heaven (Ailanthus altissima), a tree species native to China, was introduced into Europe as an ornamental plant about 250 years ago. It is known for its invasive spread with negative impacts on natural ecosystems as well as human infrastructure. Its control is inevitable in some areas, e.g. transportation corridors, for safety reasons. Furthermore, management actions are mandatory according to EU legislation, but common strategies are time-consuming, costly, only moderately effective and, in case of herbicide treatments, controversially discussed due to environmental issues. Isolate Vert56 of the vascular wilt fungus Verticillium nonalfalfae has been proven in previous studies to be highly adapted and highly virulent to Ailanthus, while inoculation of potentially susceptible tree species with this isolate showed no evidence of negative non-target effects.This study focused on non-target effects of isolate Vert56 on agricultural crops known to be generally susceptible to Verticillium spp. In a greenhouse experiment, seedlings of seven different species (including Ailanthus as a positive control) were artificially inoculated via root dipping or, in the case of seedlings of two potato varieties, by direct addition of the inoculum into the pot.All plants were subsequently assessed for symptoms during the following two months. After assessment, plants were harvested to determine dry biomass. Likewise, tissue samples were used for re-isolation of the pathogen. Besides morphological identification, 25% of the obtained fungal cultures were analyzed with species-specific primers. The pathogen was consistently detected in all species. In addition to Ailanthus, three species (Cucumis sativus, Petunia × hybrid, Spinacia oleracea) developed severe wilting symptoms and showed a decrease in biomass compared to control plants. One species, Solanum lycopersicum, displayed a decrease in biomass although only slight wilting symptoms were observed within a short period after inoculation. Humulus lupulus, Medicago sativa and Solanum tuberosum were not negatively affected by V.nonalfalfae isolate Vert56. These results indicate that safety precautions must be taken, or at least considered, when growing susceptible plants in the vicinity of Vert56-treated Ailanthus, but they also show that this biological control agent is suitable for the treatment of Ailanthus on/next to agricultural land.