Robert Blundell, Molly Arreguin, and Akif Eskalen *
*UC Davis Dept. of Plant Pathology, UC Davis, Davis, CA 95616-18 (aeskalen@ucdavis.edu)

The grapevine trunk diseases (GTDs) complex, including Esca, Eutypa dieback, and Botryosphaeria dieback, poses a major threat to the economic sustainability of grapevine cultivation, diminishing vineyard longevity and productivity worldwide. Pruning wounds represent the primary entry point for fungal pathogens responsible for these diseases and are the focus of preventative disease mitigation strategies. Our goal was to identify and characterize naturally-occurring potential biocontrol agents from different grapevine tissues/sources, including sap, pith, and wood tissue, and evaluate their antagonistic activity against GTD fungal pathogens. We recovered 11 endophytic fungi (Trichoderma spp. and Aureobasidium spp.) and bacteria (Bacillus spp.) and two epiphytes isolated from the surface of seven-day-old, untreated pruning wounds. Recovered isolates showed inhibition up to 70% against two selected common fungal pathogens responsible for GTDs in vitro. Selected isolates with potential as biocontrol agents were then evaluated in planta in the greenhouse and in three field trials (Yolo, Sacramento, and Kern Counties) and their efficacy was compared with that of commercial pruning wound protectants. In greenhouse and field trials, Trichoderma isolates from this study and Trichoderma-based commercial products were effective in protecting wounds, particularly Biotam, which conferred 88 and 100% mean per- cent disease control (MPDC) against E. lata and N. parvum, respectively. Some chemical treatments, (Topsin M + Rally and Luna Sensation) were also effective wound protectants, with at least 75% MPDC against both pathogens in Sacramento and Kern County field trials. Trichoderma-based treatments had >80% recovery from treated canes eight months from application, suggesting that effective wound colonization by biologicals is likely tied to sustained pruning wound protection.

Funding Support: Various commercial chemical/biological companies, American Vineyard Foundation