What was it all about?

From 2019 to 2022, this investment developed a survey protocol for the avocado industry to demonstrate freedom from avocado sunblotch viroid and allow healthy orchards to be certified for exports.

Although avocado sunblotch viroid has become exceedingly rare in Australia, it can create a challenge for avocado growers by impeding exports of fresh fruit. Importing countries require quarantine declarations that the fruit originates from orchards that are free of avocado sunblotch viroid, and these declarations need to be evidence-based.

The project has developed rigorous methods to demonstrate pest freedom in an orchard that meets the regulatory requirements of Australia's trading partners.

A software app was developed, which allows selection of the optimal number of trees for testing. Once the trees have been sampled, the leaves need to be processed in the laboratory, and this step can cause delays in the diagnostic process. To speed up processing of the leaves, a novel 'filter paper' sample extraction method was developed, which reduces the processing time for each sample from 2 hours to 15 minutes and dramatically decreases costs.

Avocado sunblotch viroid is pollen-transmitted, which led to the novel idea that pollen stores in beehives could be tested for the presence of the viroid and, in doing so, allow the bees to do the hard work of sampling the trees instead of humans. This novel surveillance method was successfully demonstrated in Australia and South Africa and showed much promise for future disease surveys.

The research team conducted disease surveys on the Atherton Tableland, South-East Queensland and the Riverina region, and avocado sunblotch viroid was only found at one site, supporting the notion that the avocado industry is largely free of this pathogen. The research team comprehensively surveyed the orchard where avocado sunblotch viroid was found, and four infected trees in a tight cluster were found, but with no evidence of further spread.

Over 8,000 trees and nursery plants were tested for avocado sunblotch viroid as part of the Avocado Nursery Voluntary Accreditation Scheme (ANVAS) requirements. The pathogen was never detected, suggesting that this disease management program works very effectively.

Importantly, this investment's work and protocols will have broad applicability across biosecurity threats relevant to the Australian avocado industry, now and in the future.

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Access the software app Optimisation of the sampling design for detection of avocado sunblotch viroid.