± Standard deviation; C: Control
± Standard deviation; C: Control a higher rate of establishment compared to plantlets regenerated through callus, which gave lower rate of establishment (see Tables 4.4 and 4.5). At the nursery stage, most of the plants were morphologically similar (see Figure 4.1k and l) except a few having leaves with white chlorotic patches and wavy margins.
Tissue-cultured plants of ginger could be hardened and acclimatized to the field conditions with relative ease due to the genetic nature of the zingiberaceous crops that are conventionally propagated through vegetative means. Earlier studies in ginger and other zingiberaceous crops like turmeric, cardamom, and Kaempferia support this view (Hosoki and Sagawa, 1977; Nadgauda et al., 1980; Bhagyalakshmi and Singh, 1988; Vincent et al., 1992).
Tissue-cultured plants were maintained in polythene bags for the first season and then transferred to earthern pots. Rhizomes of tissue-cultured plantlets were too small (0.7 to 3.3 g) to harvest after the first season (see Figure 4.2b) and if harvested, the rhizomes may dry up if care is not taken. The micropropagated plantlets behaved like seedlings of similar zingiberaceous crops. The size of the rhizome increased over the years and developed into normal size comparable to that of mother plants only in third year. This indicates that tissue-cultured plantlets cannot be directly used for commercial cultivation and need to be maintained for at least two to three crop seasons in the nursery before commercial planting (Nirmal Babu, 1997; Nirmal Babu et al., 1997, 1998, 2000).
The success of any in vitro culture technique depends either on the ability to clone the genotypes for production of uniform planting material or the ability to bring about variations that can be exploited in crop-improvement programs (see Figure 4.2a—h). The genetic uniformity of plants multiplied by tissue culture depends on a number of factors, with the two most important being the method of multiplication and the genotype.
Accumulated information now shows that plants propagated by precocious shoots show no more spontaneous mutation than those propagated by conventional means. Plants regenerated from callus or cell suspension cultures may show a varying proportion of structural or physiological abnormalities depending upon the species, origin, and the age of culture (Yeoman, 1986). Other factors such as growth regulators (D'Amato, 1978; Zakhlenyuk and Kunakh, 1987), composition of the culture medium (Bayliss, 1977; Feng and Quyang, 1988), culture conditions (Cerutti, 1985; Jackson and Dale, 1988), and culture method (Wilson et al., 1976) influence somaclonal variation. The reasons for variations in micropropagated plants can also be due to the variation that existed in the source plant (preexisting variation), epigenetic or physiological effects, and genetic changes (Swartz, 1991; George, 1996). Extensive studies conducted during the last decade have shown that the cell and callus cultures, especially on periodical subculture, undergo various morphological and genetic changes: polyploidy, aneuploidy, chromosome breakage, deletions, translocations, gene amplifications, inversions, and mutations (Nagl, 1972; Meins, 1983; D'Amato, 1985). In addition, there are changes at the molecular and biochemical levels, including changes in the DNA, rearrangement of genes, somatic crossing over, altered nucleotide methylation, perturbation of DNA replication by altered nucleotide pools, and slicing or activation of genes by mutations in associated noncoding regions and transposons (Scowcroft, 1984) and enzymes (Cullis, 1983; Day and Ellis, 1984; Ball and Seilleur, 1986; Brettel et al., 1986). Thus, in vitro technology is a powerful tool for the induction of much-needed genetic variability in ginger.
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