HIGH-EFFICIENCY PLANT-REGENERATION FROM CALLUS INDUCED ON MATURE INDICA RICE CARYOPSES

High frequency callus production was achieved following the culturing of mature caryopses on Murashige and Skoog (MS) medium containing MS v itamins, 10 then 5 mu M 2,4-dichlorophenoxyacetic acid, 59 mM sucrose, 3 g L(-1) casein hydrolysate and 8 g L(-1) agar. Six south-east Asian Indica rice (Oryza sativa L.) cultivars produced embryogenic structur es after 6 weeks of culture at 26 +/- 1 degrees C. Efficiency in embry ogenic response of genotypes differed, Kurkaruppan = FR13A > Khao Dawk Mali 105 = Nam Sagui 19 = RD7 > Pin Gaew 56. Additives such as mannit ol, tryptophan and ABA nor manipulation of light environment improved callus initiation or embryogenic callus formation. The use of a number of different plantlet regeneration media either free of plant growth regulators or containing auxins (indole-3-acetic acid and alpha-naphth aleneacetic acid), cytokinins (kinetin and 6-benzylaminopurine) and an ethylene producing chemical (1 -aminocyclopropane carboxylic acid) sh owed that the plant: growth regulator-free medium or the one supplemen ted with 1-aminocyclopropane carboxylic acid (5 mu M) and kinetin mu 5 mu M) were best for plantlet formation. However, a single recommendat ion could not be made for all cultivars. One further culture modificat ion involving a mild osmotic stress (polyethylene glycol 100 g L(-1)) in R-2 liquid medium enhanced plantlet regeneration in Nam Sagui 19 tw o-fold but Khao Dawk Mali 105 was recalcitrant to this treatment. Plan tlets (700) produced from all treatments subsequently developed into p lants, most of which were morphologically normal, in the greenhouse.