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Fran Pierce (left) and Mark Hanrahan check Kiona cherries for size. Kiona, a cross of Glacier and Cashmere, is one of the most recent releases from WSU.

Fran Pierce (left) and Mark Hanrahan check Kiona cherries for size. Kiona, a cross of Glacier and Cashmere, is one of the most recent releases from WSU.

Washington State University’s cherry breeder, Dr. Nnadozie Oraguzie, hopes to develop a suite of new varieties that don’t have the shortcomings of today’s leading varieties, such as susceptibility to powdery mildew.

Two disease-resistant selections from WSU’s cherry breeding program at the Irrigated Agriculture Research and Extension Center at Prosser show promise as commercial varieties because they produce high-quality fruit.

Oraguzie said he’s still collecting data on them but hopes to move towards release within a year. These would be the first varieties on the market that combine the traits of disease resistance and good eating quality. There are wild cherries with mildew resistance, but the fruit may be bitter or soften on the tree. The fruit of the two Prosser selections is actually better than of some existing varieties, he said.

“I don’t want to release something that will not be successful commercially. If I’m a consumer and I go to the grocery store, I don’t care if they have powdery mildew resistance—I want to know that the fruit quality is good. Powdery mildew resistance is for the growers.”

Oraguzie is interested in other traits as well as disease resistance. He’d like to develop a variety that is earlier than Chelan with larger fruit size, a midseason variety that is self-fertile and produces larger cherries than Bing, and blush varieties that mature very early or late in the season. He hopes to develop a whole suite of varieties, with new cherries that mature earlier than Chelan and later than Sweetheart, to expand the marketing window. As well as looking for alternatives to existing varieties, Oraguzie is hoping to develop cherries with novel traits. He’s working on freestone cherries with flesh that parts from the pits when you bite into them.

Oraguzie is evaluating seedlings from cherry crosses made each year since WSU’s cherry breeding program was revived in 2004 after a 20-year hiatus. Selections with promising attributes will be propagated and put on a fast track to commercialization. Second-stage selections will be planted in grower orchards, as well as at the Prosser center’s plots, in 2011.

“We want to give growers the opportunity to participate in evaluating these new selections earlier in the development cycle, so we get feedback before we go further with them,” he told visitors at the center’s cherry field day this summer. “This is a fast-track approach, which I think will take what the industry is doing to the next level.”

DNA markers

Oraguzie is part of WSU’s expert team in genetics, genomics, and breeding that is working on improvement of tree fruit crops.

Dr. Cameron Peace, who is based in Pullman, is developing DNA markers to assist in the selection of parents to be used in crosses and the selection of promising offspring.

By conducting DNA tests on potential parent cultivars, Peace can help the breeder select the most promising candidates to generate a new variety that carries a specific trait. In addition, markers can be used to identify fruit traits in the young offspring through DNA analysis of leaves. Since the seedlings don’t need to be grown until they fruit, the selection process is faster and more efficient. Recently, Peace and his colleagues developed a simple test for self-fertility that can be used to readily screen hundreds to thousands of plants.

Peace is also developing DNA tests to predict potential fruit size in young seedlings, in collaboration with Dr. Amy Iezzoni at Michigan State University. Large fruit is a high-priority trait in the breeding program, he said. In addition, he is working to develop genetic markets for flavor, firmness, and harvest date.

Crop load

Meanwhile, WSU genomicist Dr. Amit Dhingra and his colleagues are working to identify the genetic factors that interact with each other to determine the yield in sweet cherry. Both the rootstock and the scion may influence the number of flower buds, yet plant breeders select scions and rootstocks separately, Dhingra noted. The goal of the research is to provide information to help breeders produce rootstock and scion combinations, he said. “That will save several years of time in commercialization for new products.”

Powdery mildew

Dhingra also heads a project looking at conquering powdery mildew to reduce the need to spray cherries with fungicides. Although many plant varieties have been described as resistant, the mildew pathogen has been able to evolve and overcome the resistance over the course of time, he said. However, when resistance is conferred by a gene known as mlo, the pathogen is simply not able to recognize the plant as a host and is not able to overcome the resistance. This gene was identified in barley about 40 years ago and is functional in other crops. Derick Jiwan, a graduate student at WSU, is studying the potential for mlo-based disease resistance in sweet cherries and strawberries. “We hope that this will be another tool in our toolkit to fight powdery mildew,” Dhingra said.