Written by Per McCord, May 2021
The WSU sweet cherry breeding program (CBP) has continued to improve and expand since Dr. McCord was hired in April 2018. Laboratory and greenhouse spaces have been upgraded, and a 30 × 96-foot hoop house was recently added this spring to allow for crosses to be made under cover with potted trees.
The CBP has a four-stage pipeline. Field data, historical reports, and DNA information are used to select parents for crossing (hybridization). Crossing is done by hand, or with the use of solitary bees (mason bees) in netted cages. Some fruits are also collected from ‘open’-pollinated mother trees in the orchard. For early-ripening and interspecific crosses (crosses with other stone fruit species), a specialized technique known as embryo rescue is used to obtain viable seedlings. Seedlings are initially grown in the greenhouse during the winter and early spring. Leaf tissue is sampled for DNA extraction, and the seedlings are screened with DNA markers for important traits such as self-fertility and powdery mildew resistance. Selected seedlings are transplanted to the field in late spring as Phase 1. As the trees begin bearing, they are evaluated for several important criteria, including ripening time (early ripening is a major priority for the program), fruit size, firmness, and flavor. After several years of evaluation, superior seedlings are grafted onto a rootstock and planted in replicated Phase 2 trials. Additional data is collected in Phase 2, including cracking resistance, stem pull force, and storability. Current Phase 2 locations are in Prosser, Pasco, and Hood River. After several more years, the best Phase 2 selections are advanced to larger Phase 3 trials, all on grower farms. Evaluation criteria will be similar to Phase 2, but with the addition of running fruit over a commercial packing line. Selections that perform well in Phase 3 are released as new varieties. Currently, three selections (‘R3’, ‘R19’, and ‘R29’) are in Phase 3, with plantings in The Dalles, Mattawa, and Zillah. Since these trials were planted in 2020 and 2021, it will be several years before we have enough data to consider a release.
As part of restarted breeding pipeline, six new selections were planted in Phase 2 trials this year, with two new Phase 2 selections coming in 2022. After the newest Phase 1 trial is planted this month, there will be approximately 4,000 additional seedlings in the program, with the first expected to begin fruiting in 2022.