Research identifies protein behind costly grape leaf disease

Browning effect of Pierce’s disease on grape leaf.
Browning effect of Pierce’s disease on grape leaf. UC Davis

Scientists at UC Davis have identified a key protein at the root of a disease likely ravaging California’s grapevines and costing the state’s wine and grape industry more than $100 million yearly.

Pierce’s disease is caused by a bacteria known to hurt crops including almonds and grapes. It’s transmitted from vine to vine by a small winged insect called the sharpshooter, which lives near rivers and streams. The disease causes the yellowing or browning of grape leaves and results in leaves dropping from vines.

The disease has been a problem for grape growers since the late 1880s and decimated vineyards in the Los Angeles Basin in the 1930s and 1940s. Recently, the disease forced the replanting of 775 acres of vines in California’s North Coast and affected 25 percent of the Temecula Valley’s 3,000 vineyard acres. In the latter event, the result was an estimated $13 million in damage, according to The Wine Institute, an industry group.

It’s not well understood why the bacteria is so persistent in grape leaves, said Abhaya Dandekar, a plant geneticist at UC Davis and a co-author of the research. But the research represents a small step forward in understanding the problem.

“We stumbled on this by looking at what the bacteria is secreting,” he said. The work was published in the online journal Scientific Reports and was funded by the California Department of Food and Agriculture and the wine industry.

The research suggests that a protein secreted by the bacteria spread by the sharpshooter – and not the bacteria itself – is at the root of the spread of the disease and its persistence.

The only way to currently control the disease is by killing the sharpshooter. The research findings are expected to lead to new diagnostics and potential treatments for the disease without targeting the insect – and may help diminish the use of pesticides on grapevines, Dandekar said.

More research is needed to learn how the protein affects grape leaves, he said.

“We have no way of controlling the bacteria itself,” he said. “If you can control the bacteria, then it does not matter whether you have the insect.”

Edward Ortiz: 916-321-1071, @edwardortiz