Homonymy, synonymy and hybrid misassignments in butternut (Juglans cinerea) and Japanese walnut (Juglans ailantifolia) nut cultivars

Butternut (Juglans cinerea), a tree native to North America and Japanese walnut (J. ailantifolia), native to Japan, form the basis for a small but growing specialty nut crop industry in the eastern United States and Canada. Over the last century, Canadian and American nut tree growers, academic plant breeders and nursery owners have clonally propagated cultivars and freely exchanged scion wood, creating the possibility of misidentification. To detect homonymy, synonymy and hybrid misassignments, we used 12 highly polymorphic microsatellites to genotype most of the butternut and Japanese walnut cultivars grown in the United States and Canada. Bayesian clustering and identity analyses revealed high levels of homonymies (genetically different cultivars with the same name) and synonymies (genetically identical cultivars with different names). Over 41% of the butternut cultivars and 45% of the Japanese walnut cultivars tested had homonymies, and a majority of the cultivars in both species also had synonymies. Further, 43 entries (~15%) identified by the contributors as either J. cinerea or J. ailantifolia were interspecific hybrids. Given our results we recommend that any comparative studies on the cultivars of either species or their hybrids include reference genetic fingerprints as a part of the study.