Information gathered by Australian delegates at the recent 19th International Council for the Study of Viruses and Virus-like Diseases of the Grapevine (ICVG) Conference held in Santiago, Chile, will improve our ability to manage endemic viruses, undertake virus surveillance and improve our capacity to respond to incursions of exotic viruses.
This conference involved over 80 presentations on grapevine virus, viroid and phytoplasma epidemiology, diagnostics and plant host interactions. Presentations on the latest international Grapevine Pinot Gris Virus (GPGV) research proved very timely, given Australia’s recent detection of the virus.
Dr Fiona Constable, Senior Plant Virologist at Agriculture Victoria, attended the conference and shares some initial insights gleaned from presentations and conversations held with individual research colleagues.
- French researchers have determined that there are now four distinct groups of GPGV strains, with symptoms considered to potentially be associated with specific strains. This reasoning was not always clear, however, as often there was diversity of symptoms observed on infected vines.
- In the USA, researchers noted that vines found to be positive for GPGV were also those found to be positive for Grapevine fanleaf virus (GFLV). Their GPGV isolates were noted to cluster with asymptomatic strains from Europe.
- GPGV vine to vine spread – clustering of vines showing Grapevine leaf mottle disease is indicative of vine to vine spread of GPGV and in some vineyards, spread of GPGV increased from 20% to 77% over three years. Other studies showed a lower rate of spread.
- Mite transfer of GPGV can be relatively rapid – mites under experimental conditions, were found to acquire GPGV from both symptomatic and asymptomatic grapevines in as little as four hours.
- Alternative hosts of GPGV – Hungarian researchers reported finding GPGV in Chenopodium species (e.g. Fat Hen), Rubus species (e.g. Raspberries and Blackberries), Rosa species (e.g. Rose), Ascelpias syricaca (Common Milkweed – native to Canada) and Fraxinius species (Ash species). Significant work is still to be completed to fully explore and understand the role that these alternative hosts and potential vectors play, if any, in the epidemiology of GPGV in the viticultural context.
Further insights are being gathered and reported on in the Wine Australia-funded project titled “A comprehensive review of Grapevine Pinot Gris Virus (GPGV), including recommendations for future research, development and extension work in Australia.”
- Delegates were informed that there are now more than 80 viruses known to infect grapevines. However, the association between many newly reported viruses and disease remains uncertain. One recently reported leafroll virus, Grapevine leafroll-associated virus 13 (GLRaV-13) has though been associated with leafroll symptoms in the field.
- Newly described viruses have mostly been discovered through the use of next generation sequencing (NGS), a rapidly developing and powerful technology that has the possibility to detect all known and novel viruses in one test of a single sample. Of note, NGS has recently been used to identify significant genetic diversity among important grapevine viruses such as Grapevine leafroll-associated virus 1 (GLRaV-1) and Grapevine leafroll-associated virus 3 (GLRaV-3), which could impact detection, insect transmission and disease expression. Soon, NGS technologies may be used routinely for plant virus diagnostics to facilitate faster movement of planting material through quarantine and into certification programs. However, challenges in transitioning to NGS technology as a routine diagnostic tool for virus detection were identified. These included quality assurance, harmonizing laboratory and analysis pipelines and cost.
- Some improvements in laboratory-based tools for detection of viruses, including PCR and ELISA, were presented. One example included the use of Camelids (e.g. alpacas) to produce small antibodies for several grapevine infecting viruses including Grapevine Pinot Gris virus. These camelid antibodies have the capacity to significantly improve the sensitivity of ELISA based tests, which are generally simpler and cheaper than PCR.
- Dr Vinay Pagay from The University of Adelaide, presented his Australian research on the use of hyperspectral sensors as an alternative field-based remote sensing detection method of virus associated diseases.
- Phytoplasma research was also presented at the meeting. There are now 18 different phytoplasma species or strains that can infect grapevines, however most are associated with typical grapevine yellows disease. Grapevine phytoplasmas occurring overseas are yet to be reported in Australia. Dr Constable gave a presentation on research that was done to formally classify the Buckland Valley grapevine yellows phytoplasmas that occur in Victoria, Australia. Although the research is yet to be published, a provisional name of Candidatus Phytoplasma victoriense was proposed.
- Delegates visited the San Pedro Vineyard and Valentina grapevine nursery where efforts to mitigate the impact of virus diseases in Chilean viticulture, especially leafroll, were presented. Leafroll disease is prevalent in many Chilean vineyards and the visit highlighted the importance of high-health, virus-tested planting material to improve vineyard productivity and fruit quality.