A Core Collection for the United States Annual Medicago Germplasm Collection

The United States National Plant Germplasm System contains 3159 accessions from 36 species of annual Medicago . Although there is increasing interest in the annual medics for use in sustainable agriculture, the U.S. collection is under utilized because of lack of agronomic information. Development of a core collection could facilitate easier access to the germplasm collection and enhance its use. The core collection should consist of a sample of accessions that represents the range of variability within the germplasm collection with minimum redundancies. To select a core collection of annual Medicago species, a subset of 1240 accessions was evaluated during the summer of 1990 for 16 agronomic and morphological traits. Accessions within species were grouped by cluster analysis utilizing an unweighted pair group method with arithmetic averages. Intraspecific phenotypic diversity determined the number of accessions for that species selected for the core collection. One accession per cluster was selected for each species for the core collection. Accessions were chosen within a species to represent the greatest diversity in geographical regions. The selected core collection of 211 accessions was reevaluated during the summer of 1991. The core collection was found to represent the variability of the germplasm collection and to remain stable between the two evaluation years. This study can be used as a model method for selecting a core collection for multispecies germplasm collections.