Helping farmers avoid sour grapes: researchers develop test for hidden viruses in Ontario’s vineyards
By Michael Lim
26 September 2018
Devastating plant viruses may be putting Ontario grape farmers at risk of a serious case of “sour grapes”, but thanks to work by a team led by Prof. Baozhong Meng in the Department of Molecular and Cellular Biology, there is now a way to check for viral infections in vineyards that could help farmers get the jump on identifying which viruses are present, and where.
The wine industry may be relatively young in Canada, but that hasn’t stopped Ontario vineyards from having a big impact on the international stage. Ontario wines boast a prestigious reputation, and in 2017 the industry generated an estimated economic impact of $4.4 billion. Unfortunately, grapevines are susceptible to more viruses than any other cultivated crop, and they can create serious problems for grape producers and wineries. In 2013, many Ontario vineyards experienced large outbreaks of infection, leading to fewer, lower quality grapes and severe economic losses. In some cases, entire vineyards had to be abandoned. And just like some human viruses that cause chronic infections, damage to grapevines by viral infections may be a slow process that takes years for the growers to recognize.
Viruses are tiny, microscopic creatures that live inside the cells of other organisms; they are invisible to the naked eye, and even to some microscopes. So how can farmers detect and defend against a largely invisible enemy? For Meng, a molecular technique known as polymerase chain reaction (PCR) analysis offered the perfect tool to detect low levels of the virus that may be “hiding” in plant tissue.
Combining research techniques with practical applications is something that has always appealed to Meng, who first begun studying grape viruses in his graduate studies at Cornell University.
“I believe that integrating fundamental and applied questions is the true meaning of research,” said Meng. “Hopefully, in the end, this type of research can make a difference.”
Although viruses aren’t considered “living” organisms in the traditional sense, they still possess genetic information (i.e. RNA) that can be targeted and identified. Viral RNA targets can be used to generate DNA sequences through a process called “reverse transcription”, which can then be analyzed via PCR. PCR analysis is a technique that is akin to a rapid, tiny photocopier; it exponentially amplifies samples of DNA, allowing even the tiniest amount of a target sequence (for example, from a virus) to be readily detected. These target sequences act like barcodes, identifying specific viruses. Meng and his research team developed a modified form of PCR to identify the presence of RNA from different viruses in wine grapes. Then came the real question: what viruses are in Ontario’s vineyards, and how widespread are they?
To find out, post-doctoral fellow Huogen Xiao and Meng took ~650 leaf samples from over 30 vineyards in Ontario, representing three grape production regions. While the Niagara Peninsula made up the lion’s share of samples (87%), the Lake Erie North Shore and Prince Edward County were also chosen as they are emerging areas of grape and wine production. After performing PCR analysis, Xiao and Meng matched their sequences with 17 major viruses known to afflict wine grapes. Their findings were astonishing: 14 of the 17 viruses were detected across their samples, with ~96% of samples infected with at least one of the viruses. In fact, many samples were found to contain multiple viruses, with ~40% having at least 3 viruses.
Rather than running off and destroying vineyards, Meng offers some practical advice to farmers. He says it would be prudent to perform an assessment of vineyards to determine the extent of the viral spread (using PCR analysis for grapevines of uncertain health status), and take the necessary action to remove infected plants when infection rates are low. But Meng also admits that this is a band-aid solution at best. To achieve long-term vineyard health across not only Ontario but throughout Canada, a clean-stock program needs to be implemented that would provide grape producers with certified virus-free plants to grow. Used in several countries worldwide, this approach means growing virus-free grapevine stocks (via sanitary selection) and planting material in clean environments, with routine checks to ensure virus levels are kept low.
“Unfortunately there is no magic solution,” said Meng. “While the use of certified clean plant stocks have been used effectively in many countries, many of the major grapevine viruses are transmitted by insect vectors. Unless virus-free grapevines are used to entirely replace existing vineyards in a region, viral diseases will eventually re-emerge due to transmission by insect vectors from infected vineyards. The reality is that more fundamental research is needed to recognize and target these viruses; otherwise no alternative strategy other than clean stocks can be developed.”
In the meantime, Meng is hopeful that all levels of government agencies and the grape/wine industry will realize the importance of the clean-stock program, and is continuing to work on identifying viral infections in other grapes, such as those used to create juices or used in fruit consumption.
Other contributors to the study include the other members of the Meng research team (Mehdi Shabanian, Clayton Moore, and Caihong (Sunny) Li; Dr. Wendy McFadden-Smith (Ontario Ministry of Agriculture, Food, and Rural Affairs; OMAFRA), and participating grape growers and wineries. Funding for this research came from the University of Guelph - OMAFRA Partnerships Program (Emergency Management) and the Ontario Grape and Wine Research Inc.
Read the full study in the Virology Journal.
Read about other CBS Research Highlights.