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Ongoing project

Avocado sunblotch viroid survey (AV18007)

Key research provider: The University of Queensland

What’s it all about?

This investment is surveying for avocado sunblotch viroid in growing regions across Australia, to provide evidence to support declarations of regional or national freedom from the pathogen.

A declaration of ‘pest freedom’ – whether at a farm, region or national level – will facilitate export to countries that have their own domestic industry and may be concerned about the introduction of avocado sunblotch viroid, such as New Zealand. Understanding any current distribution of the viroid will also allow a better assessment of the risk of importing avocados to Australia from countries where the pathogen is common.

Importantly, the work and protocols this investment is establishing – such as its use of databases, its surveillance approaches and its analytical techniques – will have broad applicability across a number of biosecurity threats relevant to the Australian avocado industry, now and into the future.

Survey results for the Atherton Tableland and the Tristate areas have been collated, showing that ASBVd is both exceedingly rare in Australia and on track for eradication.

The high health status of ANVAS nurseries has been confirmed via the testing of more than 5,000 trees in two years.

A survey protocol has been developed for avocado orchards to demonstrate freedom from ASBVd, and to allow for healthy orchards to be certified for exports.

Now in the project’s second year, the number of diagnostic tests undertaken for avocado sunblotch viroid (ASBVd) is approaching 5000, all of which have provided negative test results. This provides great confidence that the pathogen is being effectively controlled in Australia.

With an Australian avocado tree population in the millions, novel methods are needed to demonstrate pest-freedom at the country level. Discussions commenced with the Department of Agriculture, Water and the Environment to develop a protocol that demonstrates a farm is a pest-free production site.

The team also investigated the potential for detecting the presence of ASBVd in an orchard by testing bee and pollen samples from hives.

Honeybees provide important pollination services but are also surrogates for biosecurity surveillance officers, as a little piece of the tree (pollen) is collected every time they visit a flower, which is then taken back to the hive. ASBVd is present in pollen grains, therefore its presence can theoretically be determined by testing the hive.

The team examined this hypothesis at locations in south east Queensland and South Africa where ASBVd-infected trees were known to occur. In both cases, ASBVd was detected in the hive samples. This provides great potential for using bee surveillance as a method to assess the presence / absence of ASBVd as part of national surveys.

Substantial progress has been made in the first year of the project, with the completion of sample tests from major nurseries along the eastern seaboard of Australia for avocado sunblotch viroid (ASBVd).

The major intervention point to control ASBVd is at the nursery stage, as the viroid is transmitted at very high rates through seed and can be multiplied if infected budwood is used for propagation or grafting tools become contaminated with sap from an infected tree.

A new avocado plant health scheme operated under the Nursery Industry Accreditation Scheme Australia has commenced, requiring that plants be tested for ASBVd.

The team have completed diagnostic testing on 2,496 plants representing 10 different cultivars from six major nurseries, with all plants demonstrated to be healthy. This result provides great confidence that the avocado industry is well on the journey to achieving freedom from ASBVd.

Good progress has also been made to develop a statistical approach for the retrospective certification of avocado orchards as being free of ASBVd. Specialised modelling work has created a simple-to-use computer program that estimates the levels of confidence that ASBVd will be detected, given nominated incidences of infection and rates of sampling.

The project team continue to engage with industry to share findings as they become available.

Related levy funds

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