48. Callus induction and plant regeneration from induced dwarf mutants of Indica rice

The successful application of plant tissue culture techniques for crop improvement requires suitable plant regeneration methods. In rice, there are many reports on successful plant regeneration from calli derived from different explants (Nishi et al. 1973; Yamada et al. 1967a, b; Furuhashi and Yatazawa 1964), including inflorescences (Kavikishore and Reddy, 1985). However, the use of tissue culture in rice improvement is limited, since the regeneration can be obtained only in limited number of genotypes. This communication summarizes our results on the efficiency of plantlet regeneration of four induced extreme dwarf mutants viz., Thed\5-8\, Thed\6-6\, Thed\7-3\ and Thed\15\, and their control, Tellahamsa (Semi dwarf) and the effect of dwarfing gene(s) on plantlet generation.

Linsmaier and Skoog's (LS) media supplemented with 2 mg/1 2,4-D (2,4- dichlorophenoxy acetic acid) was used for callus initiation from mature embryos. For plantlet regeneration, sixty day old subcultured calli were used, on twenty seven media combinations, which were grouped into three categories, viz., experimental media-1, LS basal media supplemented with varying concentrations of sucrose and sorbitol, alone or in combination with hormones; experimental media III; LS basal media with varying concentrations of sucrose and mannitol alone or in combination with hormones.

The regeneration ability of all the mutants was high on most of the media compared to their control, where only two out of 27 combinations showed high caulogenic response with 6-11 shoots. Among the mutants, Thed\6-6\ exhibited high regeneration ability with a total of 200 regenerated plantlets followed by Thed\5-8\ (1713 plantlets), Thed\15\ (1467 plantlets) and Thed\7-3\ (899 plantlets) whereas 299 plantlets were regenerated from TH control.

In this study, the mutants and the control differed considerably in their response of caulogenesis on media-I, II and III. In TH control, sorbitol/manitol added media did not promote caulogenic response. On the other hand, in mutants sorbitol supplemented media promoted organogensis significantly but the mannitol supplemented media failed to elicit the response suggesting the differntial requirements of sorbitol/mannitol in control and induced mutants, which influences the osmoticum in the organogenetic tissue. This may also be due to different dwarfing genes and their differential response to sorbitol/mannitol during differentiation.

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Kavikishor, P.B. and G.M. Reddy, 1986. Regeneration from long term cultures and selection of useful mutants in rice. In: Gene structure and function in higher plants (ed). G.M. Reddy and E.H. Coe, Jr. Oxford & IBH Publ. New Delhi, India, p. 253-255.

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Yamada, Y., T. Nishi, T. Yasuda and E. Takahashi, 1967a. The sterile culture of rice cells Oryza sativa L. and its application. In: Advances in germ free research and gnotobiology (eds) Miyakawa, M., Luckey T.D., Cleashand, CRC Press, p. 337-386.

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