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Next year, Nnadozie Oraguzie will begin field testing a new generation of mildew-resistant sweet cherry selections as he works to combine disease resistance with high fruit quality traits.

Next year, Nnadozie Oraguzie will begin field testing a new generation of mildew-resistant sweet cherry selections as he works to combine disease resistance with high fruit quality traits.

Courtesy of Washington State University

While there is keen grower interest in development of cherry varieties resistant to powdery mildew, the resulting fruit must have consumer appeal, says Washington State ­University’s cherry breeder Dr. Nnadozie Oraguzie.

Oraguzie has been collecting field and fruit quality data for several years on three sweet cherry selections (known as AA, DD, and GG) that are resistant to powdery mildew. The selections originated from material developed by former WSU stone fruit breeder Dr. Tom Toyama who retired in the mid-1980s.

Although the selections look good in terms of mildew resistance, showing no signs of disease even in unsprayed plots at WSU’s Irrigated Agriculture Research and Extension Center, Oraguzie has taken a slow approach to commercialization, concerned that fruit quality of the selections was lacking.

“From a grower standpoint, the selections are good because they have powdery mildew resistance, but the consumer buying cherries doesn’t know that,” Oraguzie said. “The fruit still has to taste good. The consumer wants a good eating experience and marketers want repeat cherry purchases.”

Following review of the fruit quality data of the mildew-resistant selections last summer, an advisory committee of industry representatives recommended that Oraguzie not move forward with the selections, he said during an interview with the Good Fruit Grower. Fruit from the resistant selections were evaluated based on fruit quality threshold values developed by industry, and they did not meet all of the thresholds, Oraguzie said.

The threshold values were developed to help quantify fruit quality attributes and aid in objective evaluations of new selections that are part of WSU’s cherry breeding program. Oraguzie said that fruit of potential new ­varieties must meet the following thresholds:

  • Weight—10 grams or more
  • Firmness—minimum of 250 gms/mm force
  • Soluble solids—20 percent (20° Brix) or more
  • Titratable acidity—0.5 percent or more

New trials

But the quest for new varieties resistant to powdery mildew will continue. Oraguzie recently made more crosses with the mildew-resistant selections, using cherry varieties with strong consumer appeal, like Sweetheart, as one of the parents. He will begin planting those hybrid selections in advanced trials next spring.

“The siblings of the AA, DD, and GG powdery mildew selections do have the disease resistance traits, but because Sweetheart is a parent, we think we’ll have better fruit quality than we had before,” he said, adding that the parents of the powdery mildew-resistant selections didn’t have the highest of eating qualities.

Commercial releases of mildew-resistant cherries are still the goal, he said. “It might just take longer than we thought.”

A mildew-resistant cherry would benefit organic cherry production because organic growers have limited options for controlling mildew.

The Washington Tree Fruit Research Commission and the Oregon Sweet Cherry Commission are helping to fund the cherry breeding program at WSU.