Abstract
The chromosomal variations occurring during the subculture of Haworthia setata (2n=14) calluses that had originated from a single callus induced from a flower bud, repeatedly subdivided in the first four culture generations, and successively subcultured for six more generations were examined. The frequency of diploid cells remained constant during subculture (ca. 50%), but that of the tetraploids gradually increased. Both hyperdiploid and hypo- or hypertetraploid cells remained as minor fractions. But, the frequency of hypodiploid cells was changeable. Though chromosome number differed significantly among some culture generations, its variation did not increase with advanced culture generations. A new variant karyotype, 7L+1M+6S, was first observed in the third culture generation, and came to constitute the modal class in three of the four primary clones, replacing the normal diploid karyotype (8L+6S). A selecting force to maintain the euploids, including the 7L+1M+6S type, was operating during callus growth. Structural changes of chromosomes found in the Haworthia callus were similar to those reported in other materials, i.e., deletions, translocations, dicentric and acentric fragments. All of the chromosomes were broken in the interstitial region, and not in the centromeric region.
