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Ongoing project

Area wide management of vegetable diseases: viruses and bacteria (VG16086)

Key research provider: The Queensland Department of Agriculture and Fisheries

What’s it all about?

Beginning in 2018, this investment is responsible for developing an ‘area wide management’ (AWM) strategy to address high-priority viral and bacterial diseases affecting vegetable crops.

This strategy will include viral diseases transmitted by thrips, aphid and whitefly pests, and phytoplasmas transmitted by leafhoppers, and will involve pest management approaches.

The project will also be keeping track of surveillance of tomato potato psyllid (TPP), through linkages with other industry TPP work.

The second major focus of the project is on managing foliar bacterial diseases.

Work will also involve developing rapid diagnostic test for key bacterial and viral pathogens.

 

Additional primer sets have been developed for specificity assays for Xanthomonas campestris pv campestris. Of the sets that pass the specificity assays they will be taken into sensitivity assays

The genomic analysis of the historical Xanthomonas campestris pv campestris has been completed and data is being collated. In addition, X. campestris pv campestris isolates that were collected have been genome sequenced and assembled.  Data analysis for this is underway.

The cucurbit viral surveillance data has been completed with conclusions underway.

The pathogenicity assay was designed to investigate whether there is a link between the genomic clonal groups and disease severity. The first round of testing in broccoli, cauliflower, and cabbage has been completed. This data is currently being analysed.

A zucchini trial in Bundaberg demonstrated the value of genetic tolerance to potyviruses as a management tool for mosaic disease. A range of insecticide treatments to combat potyvirus were also tested. The insecticides were found to be overly unsuccessful with the best treatment only reducing diseased fruit by 24 per cent. The low efficacy of insecticides to manage potyvirus is not unexpected and having field data to demonstrate this will improve messaging to industry not to use insecticides to manage these non-persistent viruses.

Trial work with bacterial pathogens affecting vegetables continued with a focus on Pectobacterium in zucchini. Trials were conducted in both WA and QLD. These trials showed that soil contaminated by the bacteria either direct through application of a bacterial suspension or via old, infected zucchini plants did not result in disease in newly planted zucchini seedlings.

Further investigation is underway on how the spread of Pectobacterium within a crop occurs with more field trials and monitoring planned.

In June 2021, a workshop on the risks of seeds introducing exotic and endemic diseases was held and attended by growers, agronomists, researchers, and biosecurity officers. The session was found to be beneficial to attendees with follow up workshops and discussions being planned.

Disease surveys in multiple states were conducted to identify viruses and diseases affecting crop regions to inform management strategies moving forward.

The team’s focus since the last project update was on continued surveillance, which was achieved despite COVID-19 restrictions and flooding impacts on trial work in New South Wales.

Seed disinfestation and indexing investigations started, with an update to be provided to the Imported Seeds Regulation Working Group, industry and biosecurity agencies at the June 2021 Hort Connections Conference.

A review of seed as a pathway for endemic pathogens and a specific review of Acidovorax citrulli was prepared. Progress was made toward diagnostic assay development, and the team completed viability and longevity assessments.

Progress continues to be shared via industry newsletters and magazines, with several presentations given at grower workshops. Information was also given as part of a PeriUrban project workshop for vegetable growers.

The project team have produced a number of fact sheets detailing the symptoms, spread and control measures for viruses affecting various vegetable crops:

There are two teams working on this project, one in NSW and one in Queensland, with the aim of investigating the most damaging bacterial and viral diseases of brassicas and cucurbits and delivering this information to industry levy payers to better manage diseases.

The project, still in its first year, has begun by developing a prioritised list of endemic and exotic diseases, which will provide guidance for the future work of the program and other research in this area.

Researchers have also produced a fact sheet on the principles of area wide management and how it applies to bacterial and viral diseases of vegetables. Researchers took the new resource to growers in collaboration with the VegNet representatives in various districts and with Ausveg Biosecurity.

Post-doctoral researchers have been appointed in Queensland and Victoria, boosting the research capacity in this area, and PhD students will come on board soon.

Surveys in multiple districts looked at key disease threats and found:

  • Tospoviruses (thrips-transmitted)
  • Serious outbreaks of foliar bacterial diseases
  • Tomato spotted wilt virus affecting radicchio, adding to the list of known hosts for this disease
  • Capsicum chlorosis virus, a serious concern for capsicum production in the dry tropics.

Activities to find out about survival and spread of diseases have begun. Weeds sampled from multiple districts are now undergoing testing for a range of different viruses, to find out if they could harbour diseases between crops.

For bacterial survival, two pot trials were completed to find out how long Xanthomonas campestris pv. campestris (Xcc) survives in field soil. Researchers found that after 2 – 3 months, soil no longer contained levels of Xcc high enough to cause disease.

Trapping of insect vectors that can carry diseases has begun, with protocols for effective trapping under development.

Research outcomes will be communicated to growers as they become available, through workshops and grower meetings, field days, industry journals, newsletters and fact sheets.

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