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Ongoing project

Improving on-farm surveillance strategies for tospoviruses and thrips to enhance the biosecurity of the nursery industry (NY19007)

Key research provider: The Victorian Department of Jobs, Precincts and Regions and University of Queensland

What’s it all about?

This investment is developing accurate surveillance tools and strategies for the detection of tospoviruses and thrips, to enable rapid responses and reduce impacts in nursery production.

Once these tools have been delivered to industry, this investment will also facilitate the adoption of best management practices by assessing how project outcomes and practices can be incorporated into existing nursery industry management and biosecurity systems such as Biosecure HACCP.

Specifically, this project will:

  • Improve understanding of the prevalence and changing populations of all tospoviruses species and thrips vectors in nursery production region
  • Assess the genetic variability and seasonal population dynamics of tospoviruses and thrips in nursery production systems, including the impact and interaction of neighbouring landscapes
  • Develop smart surveillance diagnostic tools
  • Develop, in consultation with industry members, a workable surveillance strategy for detection of exotic tospoviruses in the nursery industry.

This information will be used to support nursery industry biosecurity more broadly, by informing surveillance strategies and management practices.

Project progress continues with...

  • Preliminary in-field testing identified 18 plants, (including Gerbera, Osteospermum and tomato) from different sources infected with tomato spotted wilt orthotospovirus (TSWV) and five plants, (including sowthistle and Lisianthus), from different sources infected with impatiens necrotic spot orthotospovirus (INSV). Comparison of INSV isolates from lettuce in NSW and INSV isolates in lisianthius and sow thistle from VIC indicates that the NSW isolates are distinct from VIC isolates, suggesting two separate introductions to Australia.
  • Further testing found TSWV in 14 different plant species and INSV in three different plant species. Planning for the development of technology for detecting orthotospoviruses is underway.
  • Monitoring for orthotospoviruses in Victoria is ongoing with samples collected and tested at five different locations and across seasons in Victoria from a range of plant species, including commercial ornamental plants and weeds. Both TSWV and INSV was found in the samples with slightly higher number of TSWV recorded. Plans are underway to sequence and compare the full genome of TSWV and INSV isolates from different locations and host plants to reduce variability.
  • An evaluation is underway to ensure the RT-PCR assays for testing Orthotospovirus species remain accurate and ensure no false negative or false positive results occur.
  • More mechanical inoculation trials and transmission trials using thrips were performed with the purpose of infecting more plant species with INSV, however no successful transmission was recorded with the INSV inoculations. This work will continue as it will be important to assess the efficiency of INSV transmission by different vector species.
  • The surveillance of thrips is progressing well with results showing that the non-destructive DNA extraction method used as part of this tool is inefficient for some thrips species, compared to destructive DNA extraction methods. Modifications to the method to ensure thrips remain intact for verification of presence by morphology are being evaluated.

Substantial progress has been made investigating the diversity of tospoviruses in Australia and developing molecular methods for thrips identification.

A potentially new tospovirus, called Pterostylis blotch virus (PtBV), was discovered more than 20 years ago but there has been insufficient evidence to assess whether it was an introduced or indigenous virus, and whether it poses a threat to Australian agriculture, including the Greenlife Industry. PtBV has now been fully characterised and there is compelling evidence that it likely originated in Australia and has had an ancient association with its native orchid host plants.

Research also began to investigate ornamental plant hosts of tospoviruses in Southeast Queensland. An accidental discovery from this research was the presence of the hibiscus strain of citrus leprosis virus C2 (CLV-C2H) in a hoya plant. This was its first ever detection in Australia, demonstrating that ornamental plant species have the potential to act as movement pathways for economically important plant pathogens, as CLV-C2H can cause a serious disease in citrus crops.

Onsite surveillance for thrips and orthotospoviruses was undertaken, with leaf samples collected every two to three months from major plants in the nursery motherstock in the glasshouse, trap plants located outside the nursery, and from various weed species. These samples will be tested for the presence of orthotospoviruses later this year. In addition, leaf samples from plants infected with tomato spotted wilt virus (TSWV) and impatiens necrotic spot virus (INSV) were collected from different cut flower nurseries in Victoria. The genomes of the Orthotospovirus isolates collected from various plants and sites will be compared to improve understanding of diversity, to aid infield diagnostic assay development.

As thrips are the vectors of orthotospoviruses, it is important to check the thrips species in different nurseries and seasons. Thrips were collected from different cut flower nurseries in Victoria, in which TSWV and INSV were detected. The thrips were identified morphologically and will be confirmed molecularly. Full analysis is underway and will be reported when complete.

The project team has partnered with the largest wholesale plant nursery in Queensland to find ways to enhance its pest surveillance program. They will deliver training in taxonomic skills to the nursery to improve their identification of the major thrips species, firstly using traditional morphological methods but later using simple molecular tests. Once experimental protocols are refined, the protocols will be extended more widely within the greenlife industry. 

Thrips are important nursery pests because they cause direct feeding damage to plants but also transmit tospoviruses. Consequently, a monitoring program for tospoviruses has begun, and several perennial ornamental plants identified as reservoirs of infection, namely spider lily, bridal bouquet and hoya.

The project team were surprised to discover both a tospovirus and citrus leprosis virus C2 (CLV-C2) in a hoya plant.  This represents the first report of CLV-C2 in Australia, and the presence of a potentially damaging pathogen for the citrus industry. This result demonstrates how economically important pathogens can be spread within nursery plants. Finally, a new tospovirus has been discovered in a native ground orchid, bringing the total number of species of tospovirus in Australia to five. This discovery needs to be considered in the design of a monitoring system for tospoviruses.

Related levy funds
Details

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