Tales of a Phytopath: Grapevine Leafroll-Associated Virus (GLRaV) – Comparing Cane Samples vs. Trunk “Core” Samples
Grapevine leafroll disease (GLD) and Grapevine red blotch disease (GRBD) are two of the most serious viral diseases affecting vineyards, posing a significant challenge to the grape and wine industry in California and other major grape-growing regions. Since there is no cure for either disease, vineyard managers must rely on cultural practices for effective disease management. A combination of vector control, elimination of alternate hosts, and strategic removal of infected vines can help mitigate the spread of these viruses. However, the foundation of any successful management strategy is ensuring that new plantings are free of infection—”Start clean and stay clean.”
Sourcing pathogen-tested planting material or budwood is essential for vineyard development and regrafting efforts, but equally important is the process of sample collection for pathogen testing. The accuracy of lab results is directly influenced by the quality and representativeness of the samples submitted.
A Case Study: Sampling at a Central Valley Vineyard
In October 2024, we conducted testing at a vineyard in California’s Central Valley that was set to be regrafted with a new variety. As part of routine screening, cane samples were collected and tested for several grapevine viruses. Most of these samples tested positive for Grapevine leafroll-associated virus 3 (GLRaV-3), with some also showing coinfection with Grapevine virus A (GVA).
Following these results, the vineyard team requested a second round of testing, this time using trunk “core” samples from the rootstock portion of the vines. The idea behind this request stemmed from a common belief in the industry that sampling from different areas of the vine might yield different results.
Understanding Virus Movement Within the Vine
Upon testing, all core samples also tested positive for the same viruses. These findings aligned with what we anticipated and had discussed with the vineyard team beforehand. Phloem-limited viruses like GLRaV and GVA move systemically within the vine’s vascular system, meaning that properly collected cane samples already provide an accurate representation of the vine’s infection status.
While core sampling may seem like a way to obtain additional confirmation, it comes with its own set of considerations. The process is labor-intensive and, if not performed carefully, can lead to cross-contamination between samples. More importantly, removing core samples leaves an open wound in the trunk, creating an entry point for secondary infections, such as canker-causing fungi from the Botryosphaeriaceae family. If core sampling is necessary, proper precautions should be taken to minimize risk—this includes preventing cross-contamination during sampling and sealing wounds with an appropriate antifungal treatment to protect the vine.
Best Practices for Grapevine Sampling
The results of this case study highlight an important takeaway for vineyard managers and industry professionals: selecting the right sampling method is just as crucial as the testing itself. In most cases, cane samples provide a reliable means of detecting systemic viruses, making them a preferred choice for routine testing. However, if alternative sampling methods are considered, it is essential to weigh the potential risks and ensure best practices are followed to protect vine health.
For those looking to optimize their sampling approach, we encourage you to explore our grapevine sampling guidelines and testing services. Our team is always available to discuss the best strategies for your specific vineyard needs and to help ensure that testing is both effective and efficient.
If you have any questions or would like to learn more about our grapevine pathogen testing services, feel free to reach out. We’re here to support the industry in making informed decisions for long-term vineyard health and sustainability.
