A Wine Australia-supported PhD project at the National Wine and Grape Industry Centre has uncovered a strain of bacterium from the Pseudomonas group that is showing promise as a biological control agent of grapevine trunk diseases (GTDs).
Glasshouse studies have found it not only has the ability to reduce GTD infection in grapevines, but occurs naturally in healthy vines and persists within the plant tissues without detrimental effect.
‘The identification of a native bacterial endophyte[1] from grapevine as an antagonist towards GTDs is exciting because it demonstrates the potential for the development of alternative solutions to fungicides to combat one of the major constraints to grape production in Australia’, said Dr Jennifer Niem, who conducted the PhD research at Charles Sturt University during study leave from her position of Researcher with the University of the Philippines Los Banos.
Dr Niem’s research focused on the fungal infections that cause GTDs, which can affect all major grapevine varieties grown in Australia and lead to dieback, yield loss and even death of the vine.
A number of strains of the Pseudomonas bacteria were collected from grapevines in NSW and were tested in a laboratory setting for their ability to inhibit the fungi that cause two of the most important GTDs found in Australia: eutypa dieback and botryosphaeria dieback.
The most effective bacterial strains were further tested in the glasshouse for their ability to suppress GTD infection in grapevines. One in particular – a bacterial endophyte closely related to Pseudomonas poae – was very successful, reducing the rate of infection by 80 per cent.
‘Biochemical, microbiological, and molecular tests demonstrated that this particular strain had a range of mechanisms, including the production of an array of antimicrobial compounds, that worked synergistically to suppress GTD’, said Dr Niem.
The next stage of the research investigated whether the successful bacterium could be introduced to nursery plant materials and potted vines.
‘The outcomes indicate that the bacterial strain has potential application both as a nursery and post-planting treatment.'
‘As a nursery treatment, it may prevent grapevine cuttings from becoming infected with GTD pathogens prior to planting and this may alleviate the risk of nursery planting materials serving as a source of inoculum.
‘As a post-planting treatment, the strain may be applied on pruning wounds to protect the vines from infection or on wood dowels that can be inserted into grapevine trunk, similar to the application of Trichoderma-based products.’
Dr Niem said further work was required to assess applicability in the vineyard setting, and under the variable environmental conditions in which vineyards are established.
‘Several factors will need to be optimised before the strain can be formulated as a commercial biological control product’, she said.
Dr Niem’s research – co-funded by Charles Sturt University – contributes to a broad program of activities funded by Wine Australia that are helping Australia’s grapegrowers to get onto the front foot in the management of GTDs.
[1] Bacterial endophyte are naturally occurring microorganisms that inhabit plant tissues. They can be beneficial, neutral or pathogenic to their host plant.