Cytogenetic Research on Hexaploid Alfalfa, Medicago Sativa

SUMMARYA spontaneously occurring hexaploid plant (2 n = 6x=48) was found among white-flowered tetraploid plants of Medicago sativa.This plant was studied from a morphological and cytological point of view. All the metaphases observed showed 48 chromosomes, six of which with large satellites. Total chromosome length ranged from μ 1.34 to μ 2.25 whereas that of tetraploid ranged from μ 2.08 to μ 2.83. Most diakinesis showed bivalents and 1 or, more frequently, 2 quadrivalents. Two or more univalents were observed in 56.4% of metaphases I and lagging chromosomes, varying in number from 1 to 4, were observed in 60% of anaphases II. Hexaploid pollen stainability (81%) was the same as in the tetraploid plants used as control (80%). The pollen grains were very variable in diameter (μ) and therefore two classes were distinguished: a smaller (diameter μ. 25.5) and a larger one (diameter μ 40.0). Such variability probably means that the hexaploid plant produces many unbalanced gametes which, in association with mei..