Morphological and molecular methods to identify butternut (Juglans cinerea) and butternut hybrids: relevance to butternut conservation
Amy Ross-Davis (1), Zhonglian Huang (1), James McKenna (1), Michael Ostry (2) and Keith Woeste (1, 3)
1. Hardwood Tree Improvement and Regeneration Center, Department of Forestry and Natural Resources, Pfendler Hall, Purdue University,
715 West State Street, West Lafayette, IN 47907-2061, USA / 2. USDA Forest Service, Northern Research Station, 1992 Folwell Avenue, St. Paul, MN 55108, USA / 3. Corresponding author () / Received August 2, 2007; accepted October 15, 2007; published online May 1, 2008
Summary
Butternut (Juglans cinerea L.) is a native, cold-tolerant, hard-mast species formerly valued for its nuts and wood, which is now endangered. The most
immediate threat to butternut restoration is the spread of butternut canker disease, caused by the exotic fungus Sirococcus clavigignenti-juglandacearum Nair, Kostichka & Kuntz. Other threats include the hybridization of butternut with the exotic Japanese walnut (Juglans ailantifolia Carr.) and poor regeneration. The hybrids, known as buartnuts, are vegetatively vigorous, highly fecund, more resistant than
butternut to butternut canker disease and difficult to identify. We review the vegetative and reproductive morphological traits
that distinguish butternut from hybrids and identify those that can be used by field biologists to separate the taxa. No single
trait was sufficient to separate butternut from hybrids, but pith color, lenticel size, shape and abundance, and the presence
or absence of a notch in the upper margin of leaf scars, can be used in combination with other traits to identify butternuts
and exclude most hybrids. In at least one butternut population, reduced symptoms of butternut canker disease were significantly
associated with a dark barked phenotype. We also describe two randomly amplified polymorphic DNA (RAPD) markers that differentiate
butternuts from hybrids based on DNA polymorphism. Together, these results should assist in the identification and testing
of non-hybrid butternut for breeding and reintroduction of the species to its former habitats.
