Oregon orchardists Mitchell Huru of Hood River (left), Peter Winnick of Medford (center), and Bill Reeves of Mosier check a canker on a young Sweetheart tree on Gisela 6 rootstock in a trial at the Mid-Columbia Agricultural Research and Extension Center,
Bacterial canker is the number-one killer of cherry trees in Washington and Oregon, but some varieties and rootstocks seem more affected than others.
Dr. Robert Spotts, plant pathologist with Oregon State University in Hood River, began an experiment last spring to determine which cherry varieties are most vulnerable to the disease, and what rootstock might provide resistance. In a 300-tree plot at the Mid-Columbia Agricultural Research and Extension Center, Spotts planted five different cultivars (Bing, Rainier, Regina, Sweetheart, and Sylvia), using five different rootstocks (Colt, Gisela 6, Krymsk 5, Maxima 14, and Mazzard).
The block was planted in April 2007. In May, the trees were headed and the cuts inoculated with Pseudomonas syringae bacteria from an orchard where 70 percent of the trees had succumbed to bacterial canker.
In June, Spotts examined the trees for cankers and measured them. When results from all varieties were averaged, trees on Gisela 6 rootstocks had the biggest cankers, measuring more than 15 millimeters (2/3 inch). Trees on Maxima 14 had the smallest at 8 millimeters (1/3 inch), on average.
In terms of cultivars, Bing trees had the largest cankers, averaging 18 mm (3/4 inch), and Rainier had the smallest, at 9 mm (just over 1/3 inch).
"We’re seeing significant differences already, and they seem consistent," Spotts said. "The G.6 trees seem to have the biggest cankers, no matter what cultivar we put on it. We have very straightforward results so far."
Next spring, Spotts and his colleagues will examine every tree and measure the cankers again. "Once these trees go through the winter, there probably will be some natural infections occurring," he said.
Then, he plans to wound and inoculate them again, and go back a month later to measure the cankers. This will give him three different sets of data to compare within just over a year.
"We’ll continue doing that," he said at the center’s field day last summer. "Hopefully, the picture we’re seeing will amplify, and we’ll see clear differences."
Spotts described the trees as "sacrificial," noting that by the end of the experiment there might not be any trees left.
"You can’t afford to lose trees," he told growers, "but we can."