Genetic Resources: USDA National Clonal Germplasm Repository
Germplasm is an old term that refers to a seed, bud, sprout or other living tissue, including pollen, used to grow a new plant. The term is rooted in Latin and Greek, which obfuscates its meaning. A more clear modern term is genetic resources, which suggests that the nature of germplasm collections are to maintain genetic diversity. Germplasm collections can be private or public collections, such as an enthusiastic hobbyist, a breeder’s collection of elite material, or a federal repository.
USDA-ARS National Clonal Germplasm Repository
The germplasm used for this research is from the collection at the USDA-ARS National Clonal Germplasm Repository (NCGR) in Davis, California (NCGR in Davis). This collection houses several hundred accessions of both wild and domesticated walnut species from across Asia and North America (Juglans collection). Several collecting trips within the past decade have added new material to the Juglans collection, but most of these additions were J. regia, the domesticated species utilized for scion breeding. However, a collection by USDA-ARS scientist L.J. Grauke expanded the collection of two North American species, J. major and J. microcarpa. The latter has become a focus of research after several rounds of crown gall screening.
Utilization of the NCGR Juglans collection has included screening open pollinated seedlings for disease resistance, and creating interspecific crosses for genetic studies and as potential future rootstock varieties. The goal is to evaluate and utilize the collection for resistance to pests, diseases, and environmental stress.
Figs. 1 & 2. J. major, J. mandshurica, J. microcarpa, J. cathayensis, J. hindsii, J. ailantifolia.
Fig. 3 & 4. 10% of J. major DJUG 68.18 seedlings exhibit a red, small-plant phenotype.