Confirmation of Species Identification of Medicago NPGS Germplasm Using DNA Bar-Coding and Ploidy Level Estimation Using Genome Size Data.

Accurate identification of germplasm held at National Plant Germplasm System (NPGS) is crucial to its value and management. Species in the agronomically important genus Medicago may be misidentified as they are often recognized on the basis of relatively small differences in fruit morphology that require mature fruit for their correct identification. However, DNA bar-coding using DNA sequences of selected molecular markers can be used to confirm species identifications.

As part of a larger study of the relationships of species Medicago, including crop wild relatives, we have sampled a number of accessions of NPGS germplasm.  Most accessions appear to be accurately identified, but we have found some misidentifications as well as mixed collections.  For example, based on analyses of DNA sequence data of multiple accessions of M. constricta and M. doliata, an accession identified as M. constricta (PI 516644) is actually M. doliata.  Similarly an accession of M. monantha (PI 227050) includes seeds of two species, M. monantha and M. polyceratia.  Based on these and other results we have initiated a study of selected NPGS germplasm of the genus Medicago with the following objectives. 

1)        Confirm identification of selected accessions of secondary and tertiary wild relatives of alfalfa using DNA barcoding and ploidy level.

2)        Obtain relevant information about genetic diversity among these accessions of crop wild relatives of alfalfa. 

3)        Confirm identification of selected USDA accessions of species most closely related to M. truncatula using DNA barcoding.

4)        Provide a rough estimate of the proportion of accessions that might be misidentified within the groups sampled. 

5)        GRIN-Global: data on ploidy level for sampled accessions of Medicago will be added.  DNA sequence data will be deposited in Genbank (http://www.ncbi.nlm.nih.gov/nuccore) and cited in GRIN-Global.