By Dr. Kendra McClure, Perennia Molecular Biologist
As we prepare for the upcoming field season, it is a good time to summarize the Plant Health Lab’s virus screening work for the 2020 field season. For the past three years, Perennia staff have been visiting newly-planted vineyard blocks across the province and testing them for the presence of three grapevine viruses of economic concern: Grapevine leafroll-associated virus 1 (GLRaV-1), Grapevine leafroll-associated virus 3 (GLRaV-3), and Grapevine red blotch virus (GRBV) (Figure 1). Work in other grape growing regions on Vitis vinfera varieties suggests that such viruses may negatively affect both production and wine quality, but research on their impact in our growing region has just begun.
Figure 1. Symptoms of Grapevine Leafroll-Associated Virus in white (A) and red (B) berried varieties. Symptoms of Grapevine Red Blotch Virus in red (C) and white (D) berried varieties (OMAFRA).
The funding for this work was provided by the NSDA and focused on blocks that were planted under the Vineyard Development & Expansion Program. Testing was done using a molecular biology approach called polymerase chain reaction (PCR) or reverse-transcription PCR (RT-PCR), by Perennia’s Plant Health Lab. Each summer Perennia staffed contacted participating growers, and then traveled to their farms to conduct systematic sampling of new blocks. Our work to date has shown that all three viruses are present in new blocks, but to varying degrees. In 2020, 20 vineyard blocks were sampled across 5 counties, despite COVID-19 work restrictions. Of the three viruses tested, GLRaV-3 was the most prevalent, followed by GRBV and GLRaV-1 (Figure 2).
Figure 2. Virus infection rates for 2020 samples.
Growers whose vineyards blocks were tested received their results via e-mail in winter 2021. It would appear that newly planted material in Nova Scotia is harbouring virus, suggesting that infected material is being propagated locally, or being purchased infected, and then brought into Nova Scotia. These are Perennia’s current management recommendations:
- Once a
grapevine is infected with a virus, it will have it for life. Do not move
infected vines to other sites, and do not use infected vines for grafting.
- Monitor vines that are infected for overall health and performance (i.e., yield, Brix levels, and berry quality).
- Viruses can also be transmitted by insect vectors, therefore monitoring and management, if required, can help control spread. Scale insects and mealy bugs are known vectors of Grapevine leafroll viruses and have been confirmed in Nova Scotia. Research on insect vectors in Nova Scotia is just starting, but these insects have been implicated in the spread of viruses in other regions
- Little research has been conducted on the impact of grapevine viruses in locally grown varieties in our area to date. Researchers from Agriculture and Agri-Food Canada in Kentville are currently researching the short and long-term impacts of grapevine viruses on hybrids and V. vinifera grown in Nova Scotia.
The 2021 field season will be our last season sampling blocks planted under the expansion program at no cost to the grower. If we have yet to visit your farm, and you participated in the expansion program, please contact Kendra McClure (kmcclure@perennia.ca) to arrange a visit this summer. As always, we also offer this testing service for any local grower for a fee. Please check the Plant Health Lab’s website for up-to-date sampling and costing information (https://www.perennia.ca/agriculture/plant-health-lab/). Wishing you all a fruitful growing season!