Australian Grape & Wine would like to ensure that vineyard managers considering planting new vineyards, replanting or grafting existing ones understand the risk (or lack thereof). We are concerned about the reaction to isolated reports of crown gall symptoms associated with propagation material. Crown gall symptoms have only been reported in a small percentage of vineyards. Reports have been confined to several regions despite material being despatched all over the country. The same batches of rootlings that have expressed disease symptoms at one site have grown into healthy vines at other sites.
Perhaps unfairly, several nurseries have been implicated as having sold infected material however the cause of disease is not yet 100% clear. Curiously, these nurseries are quite independent from one another (there has been no pathogen pathway linkages established). The main commonality has been the region where symptoms have occurred. Impacted regions have generally been cold in climate and/or subject to frosts. There is a possibility that the bacterium responsible already existed in these soils. AGW has been involved in several working group sessions over the past few months which has revealed that factors other than planting material contribute to risk. It is important that industry is fully aware of the circumstances surrounding these occurrences so they can make an informed assessment before choosing whether to plant.
The science is complex.
Crown gall disease is associated with tumour inducing DNA known as a Ti – plasmid which is carried by certain Agrobacterium and Allorhizobium strains. These bacteria are widespread in soils and water globally and can also exist in plant remnants and planting material where they do not necessarily lead to disease. When present or introduced, the Ti- plasmid transfers its tumour inducing DNA into the plant cell which, upon integration, results in uncontrolled cell division and tumour formation. These bacteria can live harmlessly within plants until they take up the Ti -plasmid, starting the disease process. Due to the complex nature of how this infection arises, there is still much to be learnt regarding agrobacterium related diseases, how to detect and diagnose the causal agent and the interplay between the presence of agrobacterium, other environmental factors and symptom expression. What we do know is that risk factors include site-specific ones such as prior crown gall incidence, vine wounding from waterlogging, frost, or nematodes as well as planting material. Spread of the disease within vineyards can be reduced by implementing best practice vineyard hygiene and removal of heavily infected vines should be considered.
There are a range of risk factors to consider for any new vineyard establishment decision and Australian Grape & Wine recommends growers who have any concerns seek the advice of a viticultural consultant with experience in crown gall and/or discuss concerns with their nursery. AWRI helpdesk is well across the issues and for growers concerned regarding disease symptoms their Helpdesk contact details are here. Important work is underway investigating the bacterium to assist growers and nurseries in their decision making. In the meantime, growers might also consider assessing the experiences in and around their region and always purchase material from a VINA accredited nursery.
Wine Australia have recently published information about Crown Gall on their website.
