Articles
WALNUT GERMPLASM AT THE NATIONAL CLONAL GERMPLASM REPOSITORY, DAVIS
The Juglans (walnut) collection which is still being developed currently consists of 13 species including J. ailantifolia, J. cathayensis, J. cinerea, J. hirsuta, J. mandshurica, J. microcarpa, J. mollis, J. olanchana, J. regia, J. sinensis, J. major, J. hindsii and J. californica. The latter three species, native to western U.S.A., make up 68% of the genotypes in the collection. J. regia (English or Persian walnut) accounts for only 13% of the plant material now but is expected to increase in the future as materials from native habitats become available.
A complete list of walnut accessions at the repository is available on request.
Trees are evaluated for specific characters according to the Descriptor List as they come into bearing.
The data is compiled and maintained in the Germplasm Resources Inventory Network (GRIN), a national computer network accessible to the public.
The germplasm is available for scientific ‘study and the authors have used it to study the morphology and genetics of walnuts.
For example, a study of genetic variation in vigor, phenology and branching in juvenile California black walnut species showed that seed source was a highly significant source of variation for phenological traits and branching in J. hindsii and but that overall J. californica was more vigorous, more branched, leafed out earlier and dropped leaves later than J. hindsii. Four enzyme loci (AAT, GPI, EST, PGM) have been identified and RFLP (restriction fragment length polymorphism) markers are being developed to study variation within and between species and to characterize species relationships.