MEGACHROMOSOMES IN TISSUE-CULTURE OF ALLIUM

Chromosome studies have been conducted on the long-term callus culture s of three Allium species: A. porrum (2n = 32), A. tuberosum (2n = 32) and A. fistulosum (2n = 16). In cultures of A. fistulosum several int eresting cytological abnormalities were observed. They included direct elimination of chromatin from nuclei, multiple chromosome fusions and formation of polycentric and megachromosomes. The rate of abnormaliti es increased with the time of culture. Allium fistulosum may provide a n excellent model system to analyse cytogenetic and molecular aspects of callus - induced genomic changes and thus, somaclonal variation.