Abstract: Random amplified polymorphic DNA (RAPD) was used as a molecular tool to evaluate genomes of butternut (Juglans cinerea), Japanese walnut (Juglans ailantifolia), black walnut (Juglans nigra), Persian walnut (Juglans regia), Manchurian walnut (Juglans mandshurica), and an interspecific hybrid (J. ailantifolia × J. cinerea) for species-specific markers. Forty decamer RAPD primers generated 668 RAPD amplicons that were used to characterize bulked DNA pools of butternut, Japanese walnut Persian walnut, Manchurian walnut, and buartnut hybrids and to identify genomic regions found only in Japanese walnut or Manchurian walnut. The amplicons ranged in size from 150 to 2068 bp; sixty-five were polymorphic (9.7%) among the six taxa evaluated. Thirty-eight amplicons were unique to Japanese walnut and buartnut hybrids but absent in butternut. The RAPD markers we used were not sufficiently polymorphic to characterize intraspecific variability within Japanese walnut, butternut, or their hybrids. However, they can be used to identify hybrids based on the presence of introgressed genomic fragments inherited from Japanese walnut. They may also be useful for distinguishing whether Japanese walnut or Manchurian walnut was the parent of a hybrid lineage. The results confirmed that some hybrids can be distinguished by their morphology, and genetic similarity based on RAPDs appears to reflect known pedigree information. These RAPD markers may prove useful for conservation of butternut, an endangered North American species. These results also may prove useful for the molecular identification of species and species hybrids within Juglans.

Key words: butternut, endangered species, hybrid detection, Japanese walnut, Juglans.