Researchers solve blueberry virus mystery

For years, blueberry growers in the Fraser Valley watched helplessly as their plants died of a mysterious disease. Repeatedly, they sent their plants to the Phyto Diagnostics labs in Saanich, B.C., for testing, only for the tests to yield no answers, adding more to the mystery. 

Blueberry plants in the Fraser Valley tend to be susceptible to two diseases: blueberry shock virus and blueberry scorch virus. According to Eric Gerbrandt, research director at the BC Blueberry Council, blueberry shock virus is pollen-transmitted and typically affects plants in the first year. The plants usually recover but remain infected with the virus, which has no effect on human health but can be devastating for growers as it spreads throughout their fields with the pollen. 

“It’s a virus that can’t be controlled because it’s spread by pollen, and so we have to avoid planting varieties that are quick to become infected with the virus, and rather choose plant varieties that are slow to become infected with the blueberry shock virus,” said Gerbrandt. “The second virus is called blueberry scorch virus. It is spread by aphids, and is a more terminal condition for the plants, in that the infected plants begin to show blighting that is very similar to shock virus, blighting of the shoots, the fruit, and the flower clusters, and that reduces yields.” 

As the scorch virus spreads through a field, yields decline, and eventually farmers need to replant the infected fields. 

In recent years, growers have noticed their plants becoming infected with something that had all the hallmarks of the two common viruses, but when they sent their plants to the lab for testing, the tests came back negative.

“Several years ago, we were noticing that a lot of plants that looked like they were infected with a virus were coming back with test results that were negative for both of those viruses,” Gerbrandt told the Current. 

This presented a challenge for growers who did not know whether to leave the plants in the ground, which is what they would typically do in the case of a shock virus infection, or whether to remove the plants, which is the recommended action in the case of a scorch virus infection. 

The Blueberry Council worked with Genome B.C., which provided funding for the project, SFU, and Phyto Diagnostics to uncover the cause of the mysterious disease. 

“In 2019-2020, we started looking at this very closely, and we began with a large sampling effort. We surveyed fields across the Fraser Valley to collect samples from diseased plants and then tested them in a lab. We found that there were lots of samples that came back as negative for both viruses, but that had shown symptoms in the field, which told us that there was likely something going on with either new viruses or new strains of the existing viruses,” Gerbrandt said. 

The research and genetic sequencing showed that new strains of the shock and scorch viruses had evolved. Now, after years of work, the scientists have finally developed new diagnostic tools to identify which strains of the viruses are affecting their plants. 

“We’re currently in the final stages of developing improved diagnostic tools that capture these additional strains, so that when growers send in a sample from a diseased plant, they’re more likely to get conclusive results that tell them if it’s shock or scorch, and then they can direct their management practices accordingly,” Gerbrandt said. 

While the new diagnostic tools will help farmers differentiate between the virus strains, recommendations remain the same for managing the diseases. 

“The detection of new viral strains in the Fraser Valley doesn’t substantially change the recommendations to farmers for scorch management, which is comprised of controlling aphid populations, using a diagnostic ELISA test to differentiate between scorch and shock, and removing scorch-infected plants to reduce the spread of this virus,” Gerbrandt said. “Most farmers are doing their best to manage viral diseases, and the labs that run ELISA tests for farmers have effective tools to support these efforts.”

Even though the guidelines have not changed for managing the diseases, the new diagnostic tools will help farmers catch a disease early and take steps to contain the infection, and may save countless healthy blueberry bushes.