Ploidy determination of alfalfa germplasm accessions using flow cytometry

Determining the ploidy of germplasm is necessary before initiating breeding or genetic studies. This study was conducted to determine the ploidy of 26 3 accessions of Medicago sativa subsp. falcata Arcengeli and 20 accessions of M. saliva subsp. sativa (L.) L. & L. acquired from the USDA National Pla nt Germplasm System (NPGS). Ploidy was assessed using both now cytometry an d root tip chromosome counts. Approximately 68% of the subsp, falcata acces sions were tetraploid and 32% were diploid. In all cases where ploidy deter minations by root tip chromosome counting and flow cytometry differed, rean alysis of root tips from a new set of plants indicated the first counts wer e incorrect. The distribution of the accessions indicated that few diploids are available through the NPGS from the eastern range of the species distr ibution (Kazahkstan, Mongolia, China, and eastern Russia). Flower color var iants were identified in many subsp. falcata accessions. Three of 20 subsp. sativa accessions,were diploid, indicating they should be reclassified as M. sativa subsp. coerulea Schmalh. Flow cytometry allowed faster and more a ccurate ploidy determination than root tip chromosome counting. Ploidy dete rmination will allow researchers to more accurately identify and request ge rmplasm suited to their project.