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Washington State University’s cherry breeding program is evolving. About a dozen selections have been chosen from nearly 100 cherry rootstocks to be planted in advanced trials in the Pacific Northwest.

WSU researchers have been collaborating for nearly a decade with Michigan State University’s Dr. Amy Iezzoni in the cherry breeding project, evaluating rootstocks that were part of MSU’s tart cherry breeding program for their potential for sweet cherry rootstocks. The MSU rootstocks evaluated include crosses of Prunus cerasus, P. avium, P. canescens, and P. fruticosa.

Since 1997, 91 rootstock candidates have been evaluated in Prosser and Michigan, said Dr. Jim Olmstead, former manager of the breeding program. Researchers are looking for the most promising selections based on evaluations of tree health, vegetative growth, precocity, and flowering and fruiting ­characteristics.

Speaking at the Cherry Institute meeting last January, Olmstead said 11 rootstock selections were being propagated for testing in commercial settings.

Selections, given the names of different counties from the two states, range in size from slightly smaller than the dwarfing Gisela 5 to nearly full size (the size of Mazzard). "Some are very reduced in tree size and have potential for high crop loads," he said. "Others have reduced crop loads comparable to G.6 but with higher ­individual fruit sizes."

Tree growth has been evaluated by measuring trunk cross-sectional area, terminal and lateral shoot growth, crop load, and yield. "Everything is measured against G.6 as the standard," Olmstead said.

One selection he highlighted was Garfield, described as being the same size as G.5 but with half the crop load. "Some of our current dwarfing rootstocks have the potential for high crop loads, which can negatively impact fruit size. The breeding program is trying to identify those dwarfing rootstocks that naturally have reduced crop loads, like a G.6, but with higher individual fruit sizes."

He said that the goal is to find a rootstock that naturally results in large cherries, rather than try to make something fit the industry’s orchard systems. The overall vision is to combine genetic, horticultural, and physiological research to solve the key challenges that limit consistent, sustainable, and profitable cherry ­production.

The 11 selections will be planted in five locations with a range of elevations: Prosser, Manson, and Mattawa in ­Washington; Mosier, Oregon; and Clarksville, Michigan. The trials will include several varieties, including Bing, Sweetheart, Regina, and Rainier. Each site will test between 7 and 11 of the selections, with 500 to 600 trees per site, with the exception of the Clarksville site which will only have 70 trees (Rainier on 11 selections).

Trees in the trials are scheduled for planting in 2010, he said, adding that data will be forthcoming within a few years of planting. All of the rootstock selections are being DNA fingerprinted for ident­ification purposes to avoid any identity mix-ups.