Clarifying the ploidy of some accessions in the USDA alfalfa germplasm collection

Authors: MUHAMMET ŞAKİROĞLU, EDWARD CHARLES BRUMMER

Abstract: Cultivated alfalfa was selected from a complex taxonomic group called the Medicago sativa-falcata complex. The complex includes a number of diploid (2n = 2x = 16) and tetraploid (2n = 4x = 32) taxa. Prior information of ploidy is vital for the effective utilisation of genetic resources in alfalfa breeding programs. From the US National Plant Germplasm System, we obtained the seeds of 256 wild accessions thought to be from the 3 diploid subspecies included in the M. sativa-falcata complex, in order to determine their ploidy level using flow cytometry: M. sativa subsp. caerulea, M. sativa subsp. falcata, and M. sativa subsp. hemicycla. A majority of the accessions classified as subsp. hemicycla were found to be either tetraploid (27 out of 32) or a mixture of diploid and tetraploid (2 out of 32), suggesting that they ought to be reclassified as subsp. varia. Only 3 accessions consisted of purely diploid genotypes. Out of 71 accessions classified as subsp. caerulea, 7 were found to be tetraploid and 8 accessions were admixed. Of the 153 accessions of subsp. falcata, 67 were diploid, 82 were tetraploid, and 4 accessions showed within-accession ploidy-level variation. We recommend reclassifying the tetraploid accessions to reflect the ploidy levels detected in this study.

Keywords: Alfalfa germplasm, ploidy, M. Sativa-falcata complex

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