Researchers Making Progress on Scorch Resistance in Breeding Project

A multifaceted, multi-region research effort designed to develop varieties resistant to blueberry viruses is showing promise, according to the research director of the British Columbia Blueberry Council.

“There is a light at the end of the tunnel in terms of integrating at least one source of aphid resistance into breeding populations,” said Eric Gerbrandt in a presentation at the Oregon Blueberry Conference in Salem February 6. “But it is going to take more collection of germplasm, more genetic resources that all need to be evaluated. And it all costs money.

“But we believe that developing molecular tools, making genetic markers for these traits will speed up that process and make it more efficient,” he said.

Gerbrandt opened his presentation by noting that while multiple viruses are present in commercial blueberry fields, most are not important to growers. The two most important viruses, Scorch and Shock, can be problematic, however. A first step to properly managing for them, he said, is identifying their presence and differentiating between them, which can be difficult because they have similar symptoms.

“The reason this is important is because there are different implications for yield, depending on whether it is Scorch, which is a Carlavirus, or Shock, which is an Ilarvirus,” he said.

Gerbrandt noted that Scorch is transmitted by aphids and Shock by pollen. Scorch is a terminal disease that causes progressive yield decline in a field as more and more plants become infected. Whereas with Shock, plants typically begin to recover after the first year of infection. “Usually, a year or two later, you can’t tell that the plant had Shock, even though it is still present in the plant,” he said.

Scorch is more common in British Columbia than Shock. Whereas in Oregon, Shock is more common.

“You have much more Shock than we do, and you also have much better pollination than we do,” he said. “So, maybe that’s the reason for it.”

He added that while Scorch may be less prevalent than Shock in Oregon, it remains a threat and growers should watch for it and respond when finding it.

Management recommendations are different for the two virus diseases, he said. For Scorch, the recommendation is to control aphids and then use diagnostic tests to identify infected plants and remove them from the field. The only thing a grower can do to prevent Shock is not plant varieties that are quick to get the disease, he said.

In the coordinated multi-region, multifaceted research effort, researchers have identified short-term, medium-term and long-term objectives. Within the short-term objectives, researchers are looking to identify any new Shock or Scorch strains and access symptomology of new cultivars and genetic resources. Within the medium-term objectives, researchers are looking to develop new aphid-vector management practices and define virus, vector and plant interactions. Within the long-term objectives, researchers hope to breed cultivars with resistance or tolerance to viruses and/or vectors.

While differences in tolerance to Scorch is well documented, in that some cultivars have different reactions to it, researchers have yet to identify resistant varieties. But, he said, progress is being made on that front.

“In work done from 2019 to 2021, researchers actually found some potential aphid resistance in our breeding program,” he said. “So, the prospects for long-term solutions for Scorch look good right now.”