ABSTRACT
One of the more frequently encountered types of somaclonal variation results from changes in chromosome number, that is, aneuploidy, polyploidy or mixoploidy. Therefore, changes in ploidy observed in cultures and regenerated plants might have their origins in the source of tissue explants used. Structural changes in nuclear DNA appear to be a major cause of somaclonal variation. Tissue culture media can change the level of DNA methylation and thus may be one of the important causes of somaclonal variation. Extensive somaclonal variation can result in undesirable changes in the genetic background of regenerated plants that could limit their use as cultivars or as elite parents in breeding programmes. Although there are cases where somaclonal variation has produced plants with useful agricultural traits, as a source of variation somaclonal variation is difficult to exploit because the variation is largely unstable, mostly unpredictable and can be deleterious.
