Variation in Plants Regenerated from Tissue Culture of Tetraploid Alfalfa Heterozygous for Several Traits 1

Plants were regenerated from callus and suspension cultures of two tetraploid (2n = 4x = 32) alfalfa ( Medicago sativa L.) genotypes bred to be heterozygous for four heritable traits: i) anthocyanin pigmentation in flowers and other plant parts as conditioned by the basic color factor gene, C 2 , ii) the multifoliolate leaf trait, iii) ability to regenerate from tissue culture, and iv) cytoplasmic male‐sterility conditioned by nuclear fertility‐restorer genes. Regenerated plants were examined for shifts in expression of these traits, as well as for any other shifts in vigor, fertility, morphology or ploidy. In one callus culture cycle, 21% of 116 regenerated plants were classified as variant for one or more characters. At least 11% of regenerates lost one or more chromosomes in this callus culture cycle, with chromosome numbers among deficient plants ranging from 28 to 31. Two apparent shifts to octoploidy occurred. Approximately 60% of variant regenerates exhibited a change in chromosome number. Other variants were not due to a simple change in chromosome number. A white‐flowered variant was the result of an unstable recessive mutation of the functional C 2 allele. The frequency of somaclonal variants regenerated after suspension culture was comparable to that found after callus culture. Reculture of a 28‐chromosome variant did not result in a shift toward euploidy among 113 plants regenerated.