Field Trials of Biocontrol for Grapevine Trunk Disease

Three bacterial isolates selected from previous AVF grants (2019-2332 and 2021-2573) were utilized as biological control agents (BCAs) against fungal pathogens responsible for Grapevine Trunk Diseases (GTDs) in field conditions. The BCAs used in this study were obtained from woody tissues and the rhizosphere of grapevines grown in California; therefore, it is assumed that they have adaptations to their host and the environmental conditions of vineyards in California. The biocontrol agents were fermented for the production of secondary metabolites in liquid media and applied adopting four approaches: (i) sprayed onto pruning wounds in mature grapes; (ii) infiltrated in dormant propagation material in nurseries; (iii) injected in the trunk and cordon of mature grapevines; and (iv) poured as a soil drench treatment in the vineyard. Results of first year trials are herein presented and discussed. Among the three bacterial isolates, a positive effect was observed in treatments with Bacillus velezensis and Pseudomonas chlororaphis. These bacteria are known biocontrol agents in other plant hosts and results suggest a better performance against slow-growing GTD pathogens such as Eutypa lata and Phaeoacremonium minimum. These trials will be repeated in 2023 in order to determine the consistency of the effect of the beneficial bacteria and the influence of the season.