Genetic erosions in plant cell cultures, especially in chromosome number
and ploidy level, have now been known for over 25 years. Until the mid
-1970ssuch changes were consideredundesirable and thereforediscarded
because the main emphasis wason clonal propagation and genetic stability
of cultures. However, since the publication on somaclonal variation by
Larkin and Scowcroft (1981) there has been a renewed interest to utilize
these in vitro obtained variations for crop improvement. Studies conduc-
ted during the last decade have shown that callus cultures, especially
on peridical subculturing over an extended period of time, undergo
morpho- logical and genetic changes, i. e. polyploidy, aneuploidy,
chromosome breakage, deletions, translocations, gene amplification,
inversions, muta- tions, etc. In addition, there are changes at the
molecular and biochemical levelsincluding changes in the DNA, enzymes,
proteins, etc. Suchchanges are now intentionally induced, and useful
variants are selected. For instance in agricultural crops such as
potato, tomato, tobacco, maize, rice and sugarcane, plants showing
tolerance to a number of diseases, viruses, herbicides and salinity,
have been isolated in cell cultures. Likewise induction of male
sterility in rice, and wheat showing various levels of fer- tility and
gliadin, have been developed in vitro. These academic excercises open
new avenues for plant breeders and pathologists. Another area of
tremendous commercial importance in the pharmaceuti- cal industry is the
selection of cell lines showing high levels of medicinal and industrial
compounds. Already high shikonin containing somaclones in Lithospermum
are being used commercially.
