Host defence activation and root colonization of grapevine rootstocks by the biological control fungus Trichoderma atroviride

Several Trichoderma species can act as biocontrol agents and hold the potential to control soilborne diseases through different modes of action. Little is known about the colonization pattern of Trichoderma atroviride in grapevine roots and activation of induced systemic resistance in planta. A laboratory model was developed to assess root colonization and its impact on grapevine defence activation. Rootstock cuttings from 1-year-old dormant canes were inoculated with conidium suspensions of T. atroviride T-77 or T. atroviride USPP T1, and host and inoculum colonisation were assessed after 21 d. The two strains of T. atroviride were re-isolated from the treated plants (from 70% of the roots and 20% of crowns). Colonization rates did not depend on the Trichoderma strain or rootstock cultivar. However, up-regulation of targeted defence genes was dependent on the inoculated Trichoderma strain and rootstock cultivar. Furthermore, in leaves of rootstock cultivars 'US 8-7' and 'Paulsen 1103', genes were up-regulated which encode for PR proteins involved in plant defence or production of stilbenic phytoalexins. Trichoderma atroviride T-77 was transformed with tdTomato fluorescent protein to allow visualization by confocal laser scanning microscopy. These results give new insights into the mechanisms of grapevine-Trichoderma interactions, and allow detection of establishment of potential biocontrol agents within host tissues. Keywords. Vitis spp., Trichoderma spp., defence response.