Many parts of the whole plant may have an ultimate potential to produce callus in vitro, but it is frequently found that callus cultures are more easily established from some organs than others. Young meristematic tissues are most suitable and meristematic areas in older parts of a plant can also give rise to callus. Monocotyledons react differently and are less likely to form callus than dicotyledons (Pierik, 1987). A difference in the capacity of tissue to give rise to callus is particularly apparent in monocotyledons. For example, in most cereals, callus growth can be obtained only from organs such as zygotic embryos, germinating seeds, seed endosperm, seedling mesocotyl, and very young leaves but so far never from mature leaf tissue (Green and Philips, 1975; Dunstan et al., 1978).
Nirmal Babu (1997) reports that in ginger, callus was successfully induced in vegetative bud, young leaf, ovary, and anther tissues on MS medium supplemented with various levels (0.5 to 5.0 mgl-1) of NAA and 2,4-D for induction and proliferation of callus. Although auxins, in general, induce callus formation, this worker reported that only 2,4-D at concentrations ranging from 0.5 to 5.0 mgl-1 was effective in inducing callus in all explants tried, with the best concentration being 3 mgl-1. NAA induced a slight amount of callus at higher concentrations of 3 to 5 mgl-1 only. The explants differed in their ability to form callus. The best is vegetative bud followed by anther explant. Leaf explant gave the least amount of callus. The amount of callus produced was 2.7 g per tube in leaf and 3.4 g per tube in vegetative bud. Callus tissue was not of one kind. Strains of callus differing in appearance, color, degree of compaction, and morphogenetic potential commonly arise from a single experiment. In ginger, the callus was loose, friable, and pale yellow in color. In the subsequent cultures, the callus contained some hard organized embryogenic "lumps" (meristemoids) within the mass of loose cells (Nirmal Babu, 1997). The callus could be maintained and multiplied by monthly subcultures on the same media.
The earlier reports on callus induction in ginger were those of Pillai and Kumar (1982), Kulkarni et al. (1987), Sakamura and Suga (1989), Choi (1991b), Malamug et al. (1991), Kacker et al. (1993), Ilahi and Jabeen (1992), and Samsudeen (1996).
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