A comparison of somatic chromosomal instability in tissue culture regenerants from Medicago media Pers.

Two cultivars (Heinrichs, Reaver) and two breeding lines (Br1, Le1) from Medicago media were cultured in a media protocol consisting of a high concentration 2,4-D induction step. Regenerants were produced from all four stocks. Representative samples from each regenerant population along with the corresponding control population were cytologically analyzed for chromosomal and pollen abnormalities. While numerical changes in chromosome numbers were found in all regenerant populations, there was considerable variation between the four stock groups. Heteroploidy was observed for both hypo and hyper aneuploid regenerants, but there were no differences in pollen stainability between hypo and hyper aneuploid regenerants and 'euploid' regenerants. Tissue culture regenerants generally produced a lower pollen stainability percent as compared to control populations grown from seeds. Gross and cryptic changes in chromosomes, or hormonal carry over effects or both were considered causes for poor pollen stainability in tissue culture regenerants. Cytological analyses indicate that the cultivar might play an important role in the cytological stability or instability of regenerant populations. Exploitation of this naturally existing situation to produce 'euploid' regenerants for field experiments and to obtain gross cytological stability in somaclones is discussed.