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Ongoing project

Improving diagnostics and biosecurity for graft-transmissible diseases in citrus (CT17007)

Key research provider: NSW Department of Primary Industries

What’s it all about?

This project is responsible for supporting the NSW DPI Citrus Pathology Program in strengthening biosecurity against graft-transmissible diseases, in collaboration with other bodies including Auscitrus. The team’s activities include:

  • Working towards improved detection and diagnostics of graft-transmissible pathogens of citrus, including through assessing, developing and validating lab diagnostic procedures
  • Understanding the risk posed by newly discovered or reported graft-transmissible diseases
  • Responding to industry requests for diagnostic support.

The work follows on from earlier Hort Innovation Citrus Fund investment Protecting Australian citrus germplasm through improved diagnostic tools project (CT14009) and ties into other investments including Improving biosecurity preparedness of the Australian citrus industry (CT17001).

The project has also produced a short journal article relating to various citrus viroids which can be accessed here.

During the last six months, work was undertaken to increase the preparedness of the Australian industry and government against the threat posed by graft-transmissible diseases. The testing of survey samples from around Australia for the exotic diseases, huanglongbing (HLB) and citrus variegated chlorosis (CVC), supports the early warning system and provides evidence of absence data.

The samples were also tested for endemic diseases which expanded our pathogen collection with new accessions, enabled the robustness of test methods to be checked and increased understanding of the distribution of endemic viruses and viroids.

The ability to test citrus plant material for graft-transmissible pathogen threats was enhanced by the validation or development of new detection methods.

National diagnostic capability for significant biosecurity threats was expanded to other state diagnostic laboratories.

During the last reporting period, work was undertaken to increase Australia’s preparedness against the threat posed by graft-transmissible diseases.

  • Tests of survey samples from around Australia for exotic diseases huanglongbing (HLB) and citrus variegated chlorosis (CVC) supported the team’s early warning system and provided evidence of absence data. The samples were also tested for endemic diseases which expanded the pathogen collection with new additions, checked the robustness of test methods, and increased understanding of the distribution of endemic viruses and viroids.
  • The ability to test citrus plant material for the newly discovered citrus viroid VII (CVd-VII) was enhanced with the development and validation of a more sensitive and efficient laboratory detection method.
  • A new detection method developed by the team for citrus exocortis viroid (CEVd) was also validated and isolates of hop stunt viroid (HSVd) were cloned prior to validation of a published diagnostic test for cachexia disease. Both methods can be used in a mobile laboratory.
  • Virus testing efficiency was improved with the development of an assay that can test for citrus leaf blotch virus (CLBV), citrus psorosis virus (CPsV) and citrus tatterleaf virus (CTLV) simultaneously.
  • New sequencing technologies were used to characterise viral variants, expanding pathogen diversity understanding and assist with the development of new diagnostic tests. Focus was on citrus tristeza virus (CTV) given the complexity of its viral variants and strains and the lack of understanding of the diversity and impact of CTV on citrus trees in Australia.

Since the team’s last update, preparedness of the Australian industry against the threat posed by graft-transmissible diseases was strengthened.

Survey samples (sourced nationally) were tested for the exotic diseases huanglongbing (HLB) and citrus variegated chlorosis (CVC). The results supported the early warning system and provided evidence of absence data.

The samples were also tested for endemic diseases, resulting in the addition of new accessions to the pathogen collection, with test methods checked and an increased understanding of the distribution of endemic viruses and viroids.

The ability to test citrus plant material for the newly discovered citrus viroid VII (CVd-VII) was enhanced through the development and validation of a more sensitive laboratory detection method. An in-field diagnostic for the pathogenic citrus exocortis viroid (CEVd) was also developed and validated.

Virus testing efficiency was improved via the adoption of an assay that can test for two viruses simultaneously, with work continuing to develop more multiplex assays.

New sequencing technologies were used to characterise viral variants, expanding the team’s understanding of pathogen diversity and assisting the development of new diagnostic tests.

Commencing in early 2019, activities are well underway in strengthening biosecurity against graft-transmissible diseases in citrus. To date, the project team have:

  • Reviewed and updated the list of Australian citrus pathogens held in the NSW DPI collection to include additional pathogens not previously registered
  • Conducted a successful trial to evaluate a new rapid method of testing citrus viroids and viruses, finding that it is considerably cheaper to perform and would be useful in situations where resources are limited
  • Worked on the development of a field-based test for detecting a wide range of citrus viroid strains, with greater knowledge of the diversity of Australian viroid and viral strains achieved with the help of international experts
  • Established pot trials for ongoing research to determine the host range and potential impact of the newly discovered citrus viroid VII (CVd-VII)
  • Collected budwood from wilting trees at an orchard in Dareton NSW, which was submitted for diagnostic testing for citrus virus A (CiVA) and citrus concave gum associated virus (CCGAsV)
  • Sampled nursery trees at the Department of Agriculture and Fisheries Queensland’s Bundaberg Research Station and field trees from far North Queensland to send to South Africa for citrus tristeza virus (CTV) strain characterisation.
  • Assisted an international collaborator by validating a newly developed diagnostic tool for the early detection of huanglongbing (HLB), with further details to be provided when results are finalised
  • Successfully detected citrus stubborn disease using a new method provided by the University of California, Riverside, with other tests to now be trialled
  • Continued to process samples for the Plant Health Diagnostic Services and respond to industry enquiries.

Related levy funds
Details

This project is a strategic levy investment in the Hort Innovation Citrus Fund