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Published January 15, 2011

Mildew resistance continues to be a focus of Washington State University’s cherry breeding program. Breeder Dr. Nnadozie Oraguzie has identified another new powdery mildew-resistant selection from a cross made in 1998.

WSU scientists are seeking new sources of disease resistance and working to identify genes and genetic mechanisms underlying the resistance. A process has been developed to accurately screen seedlings for mildew resistance, and 8,000 seedlings were screened in the greenhouse in 2010.

In the long term, Oraguzie would like to develop new cultivars with multiple sources of resistance to mildew, not just a single gene.

Reporting to the Washington Tree Fruit Research Commission, which helps fund the program along with the Oregon Sweet Cherry Commission, Oraguzie said changes have been made to improve the efficiency of the breeding program. Jan Burgess, who works for the National Clean Plant Network at Prosser, has been advising on seedling development. Germination of cherry seeds is typically poor, but of the 7,000 seeds collected from crosses made in 2009, 5,000 were viable. The germination rate was over 60 percent, compared with only 5 percent in 2004, and twice what a breeding program would normally expect.

The program has also developed ways to produce seedlings that grow over three feet tall and are ready for field planting in less than a year. In 2010, Oraguzie planted more than 2,500 trees in three plantings.

Marker-assisted seedling selection was used for the first time to cull inferior seedlings based on fruit size and self-fertility. Last year, more than 60 percent of the seedlings were culled in the greenhouse.