Genetic Variability Among Eastern Black Walnut Cultivars

Black walnuts (Juglans nigra L.) are valued for their uniquely fruity flavor and are often used as an ingredient in baked goods and ice cream, or are eaten as a snack food. Although black walnuts can be harvested from wild trees, several cultivars have been selected for such characteristics as ease of cracking, size of kernel, and thickness of husks and shells. Other characteristics, such as date of budbreak, time of flowering, length of season and date of harvest, are also important adaptive traits as there is considerable variation within the species. The University of Missouri Horticulture and Agroforestry Research Center (HARC) maintains a repository of more than 65 named cultivars of black walnut valued for their kernels. The identities of each of these cultivars have been confirmed by “fingerprinting”, using a series of ten single sequence repeat microsatellite markers. A subset of cultivars maintained in the repository is used in an applied breeding program focusing on nut improvement. Average date of budbreak, flower type, bloom period, pollination date, nut season length, and harvest date of cultivars were collected from 2002 to 2006 at HARC in central Missouri.  Photographic images of black walnut fruits were also obtained in 2007 as a visual aid for identification of confirmed cultivars and can be accessed on a web site.