Issue link: http://read.dmtmag.com/i/459886
18 FEBRUARY 15, 2015 GOOD FRUIT GROWER www.goodfruit.com The discovery is likely to pique the interest of peach, cherry, and plum breeders across the United States, and it quickly led to a new collaboration between Hammerschmidt and Dr. Amy Iezzoni, the tart cherry breeder at Michigan State University. She began immediately to address some questions: First, is a Prunus maackii graft compatible with the tart cherry variety Montmorency, which dominates that industry? If it is, can it be used directly as a rootstock without any further development being needed? Second, can P. maackii be used in her breeding program to move those resistance genes into suitable rootstocks that existing varieties can be grafted onto? Third, might that resistance already be in some of the seedlings she is working with in her breeding program? She has made many crosses with tart cherry and has some hybrids, both rootstocks and scions, ready for screening. Iezzoni found that a breeder from Russia, Gennady Eremin, who bred the Krymsk rootstocks now used in cherries, had used P. maackii in his breeding program. Krymsk 6 is a quarter P. maackii, but it is not Armillaria-resistant, she said. Scientists in Russia assured Iezzoni that P. maackii had been tested and found graft-compatible with tart cherries. Ornamental stone fruit Prunus maackii is an ornamental stone fruit that is used in the landscape nursery trade. Iezzoni has con- tracted with Sierra Gold, a California nursery, to grow out P. maackii as a rootstock and to bud these liners this spring with Montmorency tart cherry and one sweet cherry. She will plant these trees at several loca- tions in Michigan and evaluate Armillaria resistance, productivity, and other horticultural characteristics. Last year, in collaboration with Dr. Nikki Rothwell at the Northwest Michigan Horticulture Research Station, she planted 12 Prunus maackii seedlings on the Old Mission Peninsula north of Traverse City, on a site known to be infected with Armillaria, to begin studies to confirm "field resistance." After one year, the trees were still healthy, but Iezzoni wants to observe them for at least four more years. A key problem with P. maackii may be its lack of precocity. It's productivity as a rootstock for cherries is not known, and Iezzoni plans to evaluate both of these factors as well as graft compatibility. "We're at the very infancy of this, but we will pursue it quite aggressively," she said. As coordinator of the COURTESY AMY IEZZONI A seedling from the cross Montmorency × P. maackii. The seedling germinated in spring 2014 and was planted at MSU's Clarksville Research Center in August 2014.