Plant Regeneration in vitro by Organogenesis on Callus Induced from Mature Embryos of Three Rice Varieties (Oryza sativa L. ssp. indica)

Callus induction and regeneration in vitro of three rice varieties (Oryza sativa L. ssp indica), Bg 94-1, Moraberekon and Bg 300 were examined. Phenotypic variations of regenerated and parent plants were compared and the method of plant regeneration was confirmed by histology. Callusing was induced by culturing the mature embryos of the three rice varieties in a liquid medium of distilled water containing 13.2 mg/L 2, 4-D and 2% sucrose for 7 days. Calli were proliferated for three weeks on solidified MS medium containing NAA and BAP at 1 mg/L each and 2% sucrose. Regeneration of calli was induced by culture solidified MS medium containing 100 mg/L tryptophan and 3% sucrose. The proliferation and regeneration media were solidified using 3 g/L gelrite. Regeneration was further stimulated by callus dehydration using silica gel and culture for 3 days on the latter medium solidified by 1% agarose. Callus induction frequencies of Bg 94-1, Moraberekon and Bg 300 were 61%, 67.5% and 55% respectively. The shoot bud induction frequencies of these varieties were 6.5%, 7.5% and 7.5% respectively. Regeneration frequencies of Bg 94-1 and Moraberekon were 100% and 43% respectively. Bg 300 calli did not regenerate. The comparison of regenerated and parent plants at a phenotypic level on maximum tiller number, maximum height and seed weight, indicated that the regenerated plants of Bg 94-1 were similar to parent plants, while Moraberekon showed variations, compared to parent plants. Histological studies revealed that regeneration occurred via indirect organogenesis from calli initiated from the rice scutellum. INTRODUCTION Progress in plant genetics and biotechnology is highly dependent on the use of in vitro techniques; hence the establishment of effective in vitro plant regeneration systems enabling a rapid production of fertile, genetically stable plants is important to biotechnologists. High frequency callus induction and efficient plant regeneration are prerequisites for the use of biotechnological approaches for rice improvement such as genetic transformation and improvement through somaclonal variation. 1 Plant Reproductive Biology, Institute of Fundamental Studies, Kandy, Sri Lanka. 2 Department of Agricultural Biology, Faculty of Agriculture, University of Peradeniya, Sri Lanka.