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 263 accessions of Medicago sativa subsp. falcata Arcengeli and 20 accessions of M. saliva subsp. sativa (L.) L. & L. acquired from the USDA National Plant Germplasm System (NPGS). Ploidy was assessed using both now cytometry and root tip chromosome counts. Approximately 68% of the subsp, falcata accessions were tetraploid and 32% were diploid. In all cases where ploidy determinations by root tip chromosome counting and flow cytometry differed, reanalysis of root tips from a new set of plants indicated the first counts were incorrect. The distribution of the accessions indicated that few diploids are available through the NPGS from the eastern range of the species distribution (Kazahkstan, Mongolia, China, and eastern Russia). Flower color variants 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 accurate ploidy determination than root tip chromosome counting. Ploidy determination will allow researchers to more accurately identify and request germplasm suited to their project.