ABSTRACT
Genetic variability has been the raw material and is important because of its unlimited scope. This phenotypic and DNA variations are determined by both genetic and epigenetic factors. Under in vitro system, where Petri dish is considered to be the breeder's field, variation has been noticed spontaneously in cultures in a large number of plant groups and several improved cell lines/crops were isolated by a selection of somatic variants (Hammerschlag et al., 1995; Karp 1995; Duncan 1997; Brar and Jain 1998; Veilleux and Johnson 1998). The utility has been well acknowledged because it often increases the possibility and efficiency of variation (Gavazzi et al., 1987). The in vitro use of mutagens (physical and chemical) has also been used simultaneously (Novak 1991) and some successful variants (Plate 15.2) with new traits are available (Brunner and Keppl 1991; Schmidt 1994). In this chapter, in vitro tissue culture variations and its various aspects have been reviewed. In vitro variation in culture: The variation in tissue culture-derived plants and their bases of occurrence have been broadly divided into 3 sections. Chimeral or pre-existing variations are those where the plant contains more than 1 genotypic constitution. The second group constitutes permanent heritable change of material, which includes both the genetic and epigenetic materials. While the last off-type variant group mimick true variations, where the changes are temporary and/or physiological.
