This project will investigate the phylogeny, pathogenicity and epidemiology of potato spindle tuber viroid (PSTVd) and related pospiviroids in Australia.

What is the biosecurity problem?

Since 2001 there have been six reported incursions of PSTVd in tomatoes in Australia. In each instance, an intense eradication program has successfully removed the source of inoculum. As a result of these successful eradication programs PSTVd is still considered a quarantine pest of significance in Australia.

It is critically important to Australian horticulture, particularly the potato industry, that Australia remains free of this destructive pathogen. An investigation into the potential entry pathways of PSTVd in tomatoes is therefore required.

Recent research in Europe has suggested that PSTVd infection may be widespread in certain wild solanaceous hosts, and that these infection reservoirs rather than seed transmissions in tomato may be responsible for outbreaks in tomato in different parts of the world. Recent research in Western Australia also suggests that certain wild non-solanaceous hosts may be involved.

The main outputs of this project are to?

• identify the strains of PSTVd and related pospiviroids that are associated with tomatoes in Australia
• assess the pathogenicity of isolates of PSTVd and related pospiviroids found in Australia on tomato and potato
• identify alternative hosts of PSTVd and the role they play in the emergence of PSTVd incursions in tomatoes in Australia
• evaluate the dynamics of PSTVd epidemics in the field, how contact transmission occurs, and the survival of its infectivity on different surfaces and the role of nurseries as potential reservoirs
• determine what types of scientific data are required to support import risk assessments of solanaceous plant products into Australia
• revise containment and eradication strategies for this harmful pests and diseases, and
• train a post graduate student in Plant Virology (viroids) and Plant Biosecurity.

Who will be the end-users of your research?

Office of the Chief Plant Protection Officer, Biosecurity Australia, Plant Health Australia, state and territory department of primary industries, vegetable industries.

This project will examine the diversity and biology of tomato-infecting geminiviruses from Australia and south-east Asia. In addition, novel strategies for the multiplexed, hierarchical detection and diagnosis of plant viruses will be developed for the improvement of plant virus incursion detection and management capacities.

What is the biosecurity problem?

Tomato leaf curl disease, caused by a complex of geminivirus species in the genus Begomovirus, is widely regarded as the most significant constraint to tomato production worldwide. Despite quarantine measures, a recent incursion of Tomato yellow leaf curl virus (TYLCV) was detected in south-east Queensland. TYLCV is now causing significant losses in tomato production in regions surrounding Brisbane and Bundaberg.

Given that the insect vector of TYLCV, the whitefly Bemisia tabaci, is present in Australia, this disease poses a huge risk for establishment and spread.

Improved virus detection and disease management strategies are needed to prevent the establishment and spread of TYLCV in Australia, and also to prevent further incursions of geminiviruses. New diagnostic strategies and technologies, focussed on hierarchical and multiplexed detection, could enable the simultaneous detection of endemic, exotic and newly occurring Geminivirus species that arise through recombination. More efficient diagnostics would greatly enhance disease surveillance and management capabilities.

The main outputs of this project are to:

• train an Australian post-graduate (PhD) student in plant virology and molecular diagnostics
• assess the recent incursion of Tomato yellow leaf curl virus in Australia
• assess the genetic diversity and biological features of geminiviruses from Australia and south-east Asia
• develop and validate diagnostic assays for a range of geminiviruses posing either a domestic or international quarantine threat, and
• evaluate a novel diagnostic platform, OptoPlex^TM nanobeads, for the multiplexed hierarchical detection of plant viruses.

Who will be the end-users of this research?

• State and Territory Department of Primary Industries
• Australian Quarantine and Inspection Service
• Universities
• CSIRO, and
• Commercial diagnostic laboratories.