Five previously undetected grapevine viruses found in South Australia

September 24, 2021September 24, 2021

Vinehealth Australia and Australian Grape & Wine advise industry of the detection of five grapevine viruses not previously known to be present in Australia. They were identified using the powerful analysis technique of High Throughput Sequencing (HTS)¹. These viruses have previously been reported overseas but studied in a limited capacity. Findings from these studies and discussions with Australian grapevine virologists suggest the impact of these five viruses on grapevine health, yield and quality, is minimal.

The national Consultative Committee for Emergency Plant Pests (CCEPP) determined that no further emergency response activities were warranted for these viruses. As such, these viruses are now considered part of the suite of viruses already present in Australia that industry manages.

While there is no immediate action for vineyard owners to take as a result of these detections, it is still pertinent to share information on these detections with industry. It also highlights the ongoing importance to manage viruses present in Australia that impact vine productivity.

VIRUSES DETECTED

A South Australian diagnostic laboratory recently reported the detection of five viruses to the Department of Primary Industries and Regions (PIRSA). Given that these viruses had not previously been detected in Australia, a response was triggered by PIRSA in partnership with Vinehealth Australia.

The viruses detected were:

Grapevine geminivirus A (GGVA)
Grapevine Syrah virus 1 (GSyV-1)
Grapevine Cabernet Sauvignon reovirus (GCSV)
Grapevine virus F (GVF)
Grapevine red globe virus (GRGV)

All detections were as a result of virus testing using HTS as part of technical/research investigations, rather than for samples submitted by commercial vineyards or nurseries for virus analysis. These five viruses are not included in standard PCR grapevine virus testing screens currently available to industry.

These five grapevine viruses were detected in mature grapevines of four winegrape varieties across three unrelated South Australian vineyards in different regions. Two of the viruses were detected in vines showing no obvious symptoms, and three were detected in vines described as showing ‘red leaves’ or ‘leafroll’ type symptoms.

WHAT DO WE KNOW ABOUT THESE VIRUSES?

Internationally, these five viruses are all relatively ‘new to science’ and have been studied in a limited capacity to date. Peer-reviewed literature reports a strong tendency for each of these viruses to occur as part of mixed virus infections, rather than alone. The impact of each of the individual viruses on grapevine health, yield and quality is therefore difficult to ascertain but appears to be minimal.

Similarly, for these South Australian samples, each of the five viruses detected were in the presence of between three to five other grapevine viruses already known to exist in Australia. Because of this, we are unable to provide reference photos of grapevines showing symptoms of each of these five viruses.

A comprehensive literature review was completed by Vinehealth Australia on each of the five viruses, a summary of which can be found below.

DETERMINATION AS TO WHETHER THESE VIRUSES ARE EMERGENCY PLANT PESTS

Information on each of the detections together with findings from the literature review and discussions with Australia’s grapevine virologists, was presented to the CCEPP. This was part of the formal notification of newly detected plant pests in accordance with the Emergency Plant Pest Response Deed (EPPRD). Australian Grape and Wine Inc (AGW) is the wine industry’s representative on the CCEPP.

The CCEPP determined that no further emergency response activities were warranted for these viruses. As such, these viruses would be considered part of the suite of viruses already present in Australia that industry manages.

Points that informed this decision would have included:

None of these five viruses are currently listed as Emergency Plant Pests under schedule 13 of the EPPRD.
None of these viruses meet the definition of an Emergency Plant Pest.
It is unlikely that eradication of these viruses would be feasible given the potential incidence of these viruses already in commercial vineyards, given:
- Unrestricted entry of potentially infected material into Australia over time with:
  - Two of the viruses (GGVA and GCSV) never being tested for at the national border.
  - Testing for the other three viruses at the national border only commencing sometime after their reporting overseas, being 2000 for GRGV, 2009 for GSyV-1, and 2012 for GVF.
- No active testing undertaken by industry for the presence of these viruses since they were first reported overseas.
- Lack of knowledge on vectors that could transmit the viruses.
- The viruses were found on numerous unrelated properties, across regions, in multiple winegrape varieties and in vines up to 40 years of age.

WHAT DOES THIS MEAN?

For grapevine material imported into Australia
- Imports found with these viruses will not be excluded from entering Australia.

For vineyard operations and general virus management
- The five viruses are not part of standard PCR virus testing screens available to industry through post-border laboratories (such as Crop Health Services (AgriBio) or AWRI Commercial Services) and as such, can only be tested for upon request. As a result, you cannot readily determine the presence of these viruses in your grapevine material. This, and the general lack of available knowledge on these viruses, means that there are no plans to develop tailored management strategies for these five viruses for industry. In situations where these viruses are detected, however, standard management practices as for other endemic viruses apply. Refer here for a range of virus management materials on Wine Australia’s website.

If you choose to specifically request HTS for virus screening, it is important for you to be aware of the potential to identify viruses not previously detected in Australia, given that it screens the genetic material of your sample against global datasets of known viruses. Any virus identified that has not previously been detected in Australia is required to be reported by the diagnostic laboratory to the State government. This in turn may result in your property being placed under a quarantine order while an investigation is conducted, and limitations placed on your vineyard operations.

ABOUT THE VIRUSES

Grapevine geminivirus A

Single-stranded DNA virus and a member of the genus Maldovirus.
First reported in 2017 in table grape accessions imported into the United States from Korea.
Previously detected in the United States, Korea, China and New Zealand, generally as part of viral complexes in both symptomatic and asymptomatic grapevines covering a large geographic area across many different Vitis species, however perhaps more commonly in table grape varieties.
Only detected in Vitis species to date.
Spread through vegetative propagation and grafting. Vector spread of this virus is unknown.

Grapevine Syrah virus 1

Single-stranded RNA virus and a member of the genus Marafivirus.
First reported in 2009 in Syrah in California.
Reported in many other countries including Chile, Slovakia, Czech Republic, Hungary, South Africa, Turkey, Spain, China and Korea, generally as part of viral complexes in both symptomatic and asymptomatic grapevines covering a large geographic area across many different Vitis species including some common winegrape varieties. Detections have also been found in various grapevine rootstocks.
Only detected in Vitis species to date.
Spread through vegetative propagation and grafting. Detected in leafhoppers from grapevines showing Syrah decline symptoms, however, no other vectors appear to have been identified or reported internationally to date, as associated with this virus.

Grapevine Cabernet Sauvignon reovirus

Double-stranded RNA virus, suspected to be a member of the genus Oryzavirus.
First reported in 2015 in Cabernet Sauvignon in California.
Reported by researchers in the United States, Brazil and China, generally as viral complexes in symptomatic grapevines.
Only detected in Vitis vinifera to date from very limited testing internationally.
Spread through vegetative propagation and grafting. Vector spread of this virus is unknown.

Grapevine virus F

Single-stranded RNA virus and a member of the genus Vitivirus.
First reported in 2012 in Cabernet Sauvignon in the United States.
Reported by researchers in a number of countries including the United States, South Africa, Iran, Greece and Tunisia, in some cases in grapevine material originating from a wide range of varieties and origins worldwide. Where full virus screens were conducted, detections of GVF have generally been noted as mixed virus complexes in grapevines symptomatic of leafroll disease.
Only detected in Vitis species to date.
Spread through vegetative propagation and grafting. Other viruses in the same genus – grapevine virus A (GVA) and grapevine virus B (GVB), have been found to be vectored by mealybugs and scale, although there is no evidence of this to date for GVF.
Viruses of the genus have been associated with the grapevine rugose wood complex, which affects yield and quality and the production of wood for propagation. This complex has been associated with scion/rootstock graft incompatibility and is of major importance to viticulture worldwide. Despite this, there has been no proven cause-effect relationship for graft incompatibility or other symptoms as a result of the presence of GVF, unlike GVA and GVB in particular.

Grapevine red globe virus

Single-stranded RNA virus and a member of the genus Maculavirus.
First reported in 2000 in Red Globe in Southern Italy.
Reported by researchers in a range of countries including Italy, France, China, Brazil, Germany, Spain, Iran and USA, generally as part of mixed virus complexes.
Infections have been concluded as apparently symptomless and potential effects, if any on grapevines, remain unknown.
Only detected in Vitis species to date.
Spread occurs through vegetative propagation and grafting. Vectors, if any, are unknown.

1 HTS is an extremely powerful new research tool, with the ability to detect viruses present in biological fluids if their sequence is already known or close to that of viruses that have already been described.