Constitutive heterochromatin DNA polymorphisms in diploid Medicago sativa ssp. falcata

A Giemsa C-banding technique was used to study the amount and location of constitutive heterochromatin in diploid (2n = 2x = 16) Medicago sativa ssp. falcata (L.) Arcangeli. Most accessions had the standard C-banding pattern with centromeric bands on all the chromosomes and a prominent heterochromatic band at the nucleolar organizer regions (NOR) of the satellited (SAT) chromosomes. However, we observed in various accessions that constitutive heterochromatic C-bands can exist at the telomeric ends of all the chromosomes. Interstitial bands occurred on the short arms of all chromosomes except for chromosome 3 and on the long arms of chromosomes 1, 2, 3, and 6, only. Rearranged chromosomes such as isochromosomes have been observed for the short arms of chromosomes 2 and 6. This is the first report on the existence of C-banding polymorphisms and the detection of putative isochromsomes in the chromosomes of diploid ssp. falcata which could have contributed to the variation observed in cultivated alfalfa.