A core collection of 1706 annual Medicago accessions was developed from the analysis of evaluation and passport data of 16,306 Medicago accessions representing 34 species and 37 sub-species (Ellwood et al 1999). The core collection was developed by maximizing the diversity, measured as mean Euclidean distance, from within groups of accessions defined by species, subspecies and geographic origin. Grouping was performed sequentially, such that species groups were formed first, subspecies groups were then found within each species, and geographical origin within each species-subspecies group was then taken into account.

Evaluations for 27 medic descriptors (IBPGR 1991) were carried out for the 16,306 accessions from 1968 to 1994. Diversity within each accession was measured as the mean Euclidean distance of each accession to all other accessions. The core collection was developed by selecting 0.5% of the accessions with low Euclidean distance (representing typical accessions), and 3.0% of the accessions with high Euclidean distance (representing accessions with more unusual characters) from each group, resulted in a core collection of 1705 accessions (10.4% of the total collection containing a complete dataset).

The ranges and standard deviation of observed measurements of 27 characters in the APG and core collection are shown in Table 2. Full observation data is available on Genesys and at https://apg.pir.sa.gov.au/gringlobal/descriptors

As the core collection is very large, we encourage users to consider refining the core for their requirements and order accessions from each species group, by geography (or climate), or from the mini-core developed for M. truncatula (Ellwood et al 2006).

References:

International Board for Plant Genetic Resources. 1991. Descriptors for Annual Medicago. Rome, Italy.
Skinner, D.Z., Bauchan, G.R., Auricht, G., Hughes, S. (1999a) In “Core collections for today and tomorrow”, Eds. Johnson, R.C. and T. Hodgkin. International Plant Genetic Resources Institute, Rome, Italy.
Skinner, D.Z., Bauchan, G.R., Auricht, G., Hughes, S. (1999b) A Method for the Efficient Management and Utilization of Large Germplasm Collections. Crop Science, 39, 4 1237-1242.
Ellwood, S.R., D’Souza, N.K., Kamphuis, L.G. Burgess, T.I. Nair, R.M., Oliver, R.P. (2006) SSR analysis of the Medicago truncatula SARDI core collection reveals substantial diversity and unusual genotype dispersal throughout the Mediterranean basin, Theoretical and Applied Genetics, 112, 5, 977-983.