Somaclonal Variation — Origin, Induction, Cryopreservation, and Implications in Plant Breeding

Abstract

It has been known for over 25 years now that plant cell and tissue cultures undergo genetic erosions and show changes of various types, especially in chromosome numbers and ploidy level (Partanen 1963; D’Amato 1965; Murashige and Nakano 1966). However, till the mid 1970’s such changes were considered undesirable and were therefore discarded because the main emphasis was on clonal propagation and genetic stability of the cell cultures. Extensive studies conducted during the last decade have shown that the cell cultures, especially on periodical subculturing, undergo various morphological and genetic changes, i.e., polyploidy, aneuploidy, chromosome breakage, deletions, translocations, gene amplification, inversions, mutations, etc. (see Nagl 1972; Meins 1983; D’Amato 1985). In addition, there are changes at the molecular and biochemical levels (Day and Ellis 1984; Landsman and Uhrig 1985; Ball and Seilleur 1986) including changes in the DNA (Berlyn 1982; Cullis 1983), enzymes (Brettell et al. 1986b), gliadin (Cooper et al. 1986), etc. Since the publication of Larkin and Scowcroft (1981) there has been an upsurge of interest, and the attitude toward these changes has shifted to using the somaclonal variations for plant improvement; they are intentionally induced and much sought after.