Mildew-resistant cherries awaited
Resistant varieties could be particularly interesting for organic growers.
WSU cherry breeder Nnadozie Oraguzie explains the goals of the breeding program during a field day at Prosser.
Published January 15, 2011
Washington State University is evaluating three powdery mildew-resistant cherry selections in grower trials. The industry is eagerly awaiting their release, but cherry breeder Dr. Nnadozie Oraguzie says he needs to collect more data on fruit quality before going forward.
The advanced selections have shown no symptoms of mildew even in unsprayed plots at WSU’s Irrigated Agriculture Research and Extension Center at Prosser.
The selections originated from material developed by former stone fruit breeder Dr. Tom Toyama. Toyama identified a seedling that showed no signs of mildew even in greenhouse conditions, where the disease tends to be rampant, and made a note to continue to watch the seedling when it was planted out in the field at Prosser. In a field study, when trees grafted with budwood from the selection were artificially inoculated with the powdery mildew fungus, there were still no signs of infection.
After Toyama retired in the mid-1980s, soft fruit breeding at Prosser lapsed. In 1998, Jim Olmstead, a WSU graduate who was at Prosser working on his master’s thesis, became interested in the mildew-resistant material. His thesis topic was inheritance of powdery mildew resistance in cherry. In the course of his research, he crossed the resistant material with the susceptible varieties Bing, Van, and Rainier to calculate how the gene was inherited.
“If we understand the inheritance, we know how many seedlings we can expect to be resistant and the level of resistance we might expect to see in the progeny,” he explained.
WSU cherry horticulturist Dr. Greg Lang had trees of the seedlings from those crosses propagated and planted out at Prosser.
Olmstead then went to Michigan State University to pursue a doctorate, and Lang also left Prosser in 2000 for a position at MSU. Lang had second-generation trees propagated from the selections to plant at MSU.
Dr. Matt Whiting, who succeeded Lang as cherry horticulturist at Prosser, revived the breeding program in 2004, working in collaboration with MSU tart cherry breeder Dr. Amy Iezzoni.
In 2006, Olmstead moved back to Prosser as a postdoctoral researcher and continued to look at the mildew-resistant material he had been working with. He arranged for small trials of 10 to 15 trees to be planted in 2008 in the orchards of grower cooperators in Washington: Mark Hanrahan at Buena, Bob Crane at Pateros, Norm Gutzwiler in Wenatchee, Dave Allan in the Yakima Valley, and Don Olmstead at Grandview. The following year, larger trials were planted in orchards owned by Chelan Fruit Cooperative in Manson and Sagemoor Farms in Pasco.
In 2008, Olmstead left Prosser to take a position with Washington State University Extension in Yakima, and Dr. Nnadozie Oraguzie was appointed cherry breeder at Prosser. Olmstead is now the blueberry breeder at the University of Florida.
Oraguzie, with the help of the Washington Tree Fruit Research Commission, is analyzing data on yield and fruit quality from the plots in commercial orchards, before deciding whether to recommend that WSU go forward and release them as commercial varieties.
Growers have expressed frustration about the length of time it is taking to release the varieties. Fred Valentine of Wenatchee said he hoped the mildew-resistant varieties would be released soon because the fruit he’s seen on trees at the Prosser station looked good.
Oraguzie said disease resistance is important to growers, but the cherries also need to provide a good eating experience for consumers. “We’re trying to collect more yield and fruit quality data, so we will be confident that when we release the variety it will have good fruit quality,” he said during the Research Commission’s cherry research review in November. The commission and the Oregon Sweet Cherry Commission help fund the breeding program.
Dave Allan said one of the selections might be a good fit for organic cherry growers who have limited options for controlling mildew. The fruit quality might not be as good as some commercial varieties, but the disease resistance would be useful.
“I don’t think I could recommend the cherry to be planted, but I think I could recommend that growers take a good look at it and see what they can do with it,” he said. “I think it would only be in the organic arena at the present time.”
According to Oraguzie, two of the advanced selections have been released to nurseries to generate virus-free planting material in readiness for when they are released commercially.
“Things are progressing along,” commented Dena Ybarra at Columbia Basin Nursery in Quincy, Washington. “But it’s slower than everyone wants.”