36. Plant regeneration from calli for in vitro selection in rice

Laboratoire de Cytogenetique, Universite Catholique de Louvain, Place Croix du Sud 4, 1348 Louvain-la-Neuve, Belgium

It has been suggested that in vitro culture could become an efficient tool for rice breeding. Callus induction and plant regeneration have been achieved from microspores and various somatic tissues. According to Oono (1978, 1982), a very high frequency of modifications are induced in vitro cultures and some of them are very useful. In vitro selection at the cellular level have resulted in plants tolerant to salt (Croughhan et al. 1981), aluminium (Swaminathan 1982) or with an increased amino acid content (Schaeffer 1981).

The purpose of our research, which is supported by an EEC contract, is the in vitro selection of spontaneous or induced mutants for characters important in some African rice growing countries, such as resistance to bacterial toxins, and tolerance to salinity or low temperature.

The experimental materials used were mature embryos, and root and leaf fragments, but plant regeneration was obtained from embryo calli only. Among the culture media we have tested, the best results were obtained with LS (Linsmaier and Skoog 1965). LS medium with 2,4-D (0.5mg/l), 6- benzylaminopurine (1 mg/l) and naphthaleneacetic acid (1 mg/l) gave more than 90% callus induction. After one or two subcultures, different cell lines were established which differed in their growth rates and their morphogenetic potential.

Half-strength LS medium was used for inducing organogenesis from the calli. At the present, the proportion of the calli regenerating at least one viable plantlet is between 45 and 55%. The role of several growth regulators and other substances such as benzylaminopurine, NAA, 2,4-D, TIBA, coconut water, adenine sulphate is now being tested. Coconut water improves the regeneration, but most non-regnerating calli become necrotic after 10 to 20 days in the absence of auxins. At low concentration, 2,4-D reduces the incidence of necrosis, but it has a negative influence on the differentiation.

Plant regeneration is generally obtained through somatic embryogenesis. A large number of small embryoids are formed; often more than a hundred from one callus. Many of them do not develop as their germination is poor and irregular. Nevertheless, some calli gave rise to more than 10 plantlets. New culture media and treatments are being tested in order to improve the number of recovered viable plants.

Croughan, T.P., S.J. Stavarek and D.W. Rains, 1981. In vitro development of salt resistant plants. Env. Exp. Bot. 21: 317-324.

Linsmaier, E.M. and F. Skoog, 1965. Organic growth factor requirements for tobacco tissue culture. Physiol. Plant. 18: 100-127.

Ocono, K., 1978. High frequency mutations in rice plants regenerated from seed callus. 4th Int. Congr. Plant Tissue and Cell Culture, Calgary, p. 52.

Ocono, K., 1982. Characteristics of mutation in cultured rice tissues. Proc. 5th Int. Congr. Plant Tissue and Cell Culture, p. 409-410.

Schaeffer, G.W., 1981. Mutation and cell selections: increased protein from regenerated rice tissue cultures. Env. Exp. Bot. 21: 333-345.

Swaminathan, M.S., 1982. Biotechnology research and Third World agriculture. Science 218: 967-974.