CYTOGENETIC STUDY ON A TETRAPLOID PLANT AT THE DIPLOID CHROMOSOME LEVEL

Abstract

It was ascertained that the species from which Grimm alfalfa presumably originated, viz.; Medicago sativa and M. falcata, may freely exchange genetic material without evidence of a sterility barrier. Consequently a polyhaploid obtained of Grimm may be considered as comparable to natural diploids.The polyhaploid showed some impaired morphological and physiological characters and pronounced meiotic abnormalities. The single genome (x = 8) of the polyhaploid was found to be almost non-functional. Inheritance of purple color indicated a potential autotetraploid mode of transmission of characters.The polyhaploid was raised back to the tetraploid chromosome level by chromosome doubling and compared to its original and to Grimm. The somatically chromosome-doubled counterpart was found to be a close replica of the original polyhaploid. An assumption that an accumulation of detrimental recessive genes may remain latent at the tetraploid level, and may be expressed upon later reduction to half of the genic variability as in the polyhaploid and its somatically chromosome-doubled derivative, is advanced to explain the observed phenomena.Phylogenetic, breeding, and culture-historical aspects of the results are discussed.