Content area
Full text
ABSTRACT
A cytogenetic investigation was conducted on four historically putatively distinct nondormant alfalfa germplasm sources, African, Chilean, Peruvian, and Indian tetraploid alfalfa [Medicago sativa ssp. sativa (L.) L. & L.; 2n = 4x = 32]. C-banding, image analysis, and cluster analysis was used to test the hypothesis that chromosome structure differed among the four nondormant alfalfa populations. Cytogenetic analyses revealed polymorphisms for heterochromatic DNA in the number and location of constitutive heterochromatic DNA both within and among genotypes. However, this variability did not prevent recognition of homologous chromosomes. Karyotypes of Peruvian and Indian populations were developed. The reference African population was used to compare the karyotypes of Peruvian and Indian populations as well as the previously published Chilean population. In general, the number of heterochromatic DNA bands was similar for the African, Chilean, and Peruvian populations; however, the Indian population had significantly fewer heterochromatic bands than the other three. Cluster analysis based on all eight chromosomes yielded no clear separation of the nondormant alfalfa populations possibly because of the lack of chromosomal rearrangements, similar genetic backgrounds of the initial introductions, intercrossing of the different sources, genetic drift during maintenance, and/or common genetic backgrounds of the original parental germplasm sources.
AFALFA, the most important forage crop grown in the USA, is primarily harvested as hay for animal consumption but is also an important component of pastures. Nondormant alfalfa is particularly important in the southwestern USA where, under irrigation, it can be grown throughout the year producing 52 Mg ha^sup -1^ yr^sup -1^ compared with 22 Mg ha^sup -1^ yr^sup -1^ for alfalfa grown under varied conditions in the midwestern USA. Nondormant alfalfa is characterized as having rapid regrowth after harvesting in the autumn but it is not winter hardy (Barnes et al., 1978; Teuber et al., 1998).
Nine historically distinct sources of alfalfa germplasm, African, Chilean, Flemish, Indian, Ladak, Peruvian, Turkistan, M. falcata, and M. varia, were introduced into different U.S. regions between 1850 and 1947 (Barnes et al., 1977). Nondormant alfalfa was introduced into the new world initially by the Spanish as early as the 16th Century. The Chilean and Peruvian types spread into the southwestern USA with missionaries as early as 1850. The Indian types were introduced into California in 1913 (Barnes...