Controlling Grapevine Trunk Diseases in California

A total of 20 vineyards from 10 counties across California were sampled during summer 2019. Cordon, trunk and root tissue samples were collected from mature vines using non-destructive methods in order to isolate, analyze and study endophytic bacterial communities between healthy looking and diseased vines exhibiting typical trunk disease symptoms. A collection of over 1,344 endophytic bacterial isolates was obtained and screened for their potential antifungal effect against the main GTD-causing pathogens in vitro. A first screening using Neofusicoccum parvum indicated that 24.7% of the collection caused over 40% of mycelial inhibition (333 isolates), and these were further tested against Diplodia seriata, Diaporthe ampelina and Eutypa lata. A subset of 90 bacterial isolates was selected by their biocontrol potential (higher inhibition percentages) against the four pathogens. Phylogenetic analyses showed that 70% correspond to Bacillus velezensis (65 isolates) whereas the remaining correspond to a broad range of Gram positive and Gram-negative bacteria, some of them known to secrete antifungal compounds. Different species are currently being tested in greenhouse experiments to elucidate their capability to colonize grapevines and protect them from trunk disease development. Furthermore, health status and trunk disease incidence were evaluated in vines that were treated with pesticides using vacuum infiltration in three commercial nurseries over the summer of 2019 and planted in the UC Davis Plant Pathology field station in October 2019. Even though the final evaluation of treated vines will be done at the end of 2021, preliminary field observations showed different levels of performance among treatments. Preliminary isolations from plant tissues showed that there were two predominant fungal groups: potentially pathogenic (Fusarium and Botryosphaeriaceae) and beneficial/plant protective (Trichoderma and Clonostachys).