Exploring the interactions between bacterial endophytes and trunk disease pathogens of grapevine

In recent years, the use of endophytes in the management of plant disease has gained popularity as an alternative to chemical application, driven in part by concerns for human and environmental safety with the use of fungicides. Some endophytic bacteria of grapevines including Pseudomonas species may play a role in the disease suppression of GTDs in the vineyard. The diversity of bacterial endophytes associated with grapevine wood was analysed using next-generation Illumina sequencing using the 16S rDNA (341F/806R) region. For Harden and Hunter Valley, two important grape-growing regions in NSW, the endophytic bacterial community within vineyards known to be infected with grapevine trunk disease (GTD) were assessed, with DNA samples extracted from asymptomatic and symptomatic grapevine tissue. Pseudomonas predominated the bacterial community in the asymptomatic grapevine tissue examined from both locations, comprising 56-74% of the total population. In contrast, the Pseudomonas population in GTD symptomatic tissues were significantly lower representing 29% and 2% of the bacterial microbiota in Harden and Hunter Valley, respectively. Targeted isolation of fluorescent Pseudomonas was done and 10 out of 47 strains exhibited antagonism against 9 Botryosphaeria dieback (BD) and 3 Eutypa dieback (ED) pathogens in dual culture assay. Using single node dormant canes, the efficacy of the 10 most promising biocontrol agents (BCAs) in suppressing GTD infection in grapevine tissues was tested. BCA 17, BCA 14, and BCA 13 showed highest reduction in number of canes infected in which Neofusicoccum luteum was reisolated in only 0-11% of the canes after 14 days. Control canes had 100% infection. BCA 17 was also found to effectively reduce GTD infection by 80% relative to the control in potted grapevines. Rifampicin-resistant strain of Pseudomonas was generated to assess the establishment of the potential BCA in grapevine tissues and the bacterium was found to persist in the host tissues for up to 6 months. The presence and abundance of Pseudomonas in grapevine tissues indicate its ability to colonise the host tissue as an endophyte and to perhaps supress GTD infections.