High-Efficiency Plant Regeneration From Callus Induced on Mature Indica Rice Caryopses

Abstract

High frequency callus production was achieved following the culturing of mature caryopses on Murashige and Skoog (MS) medium containing MS vitamins, 10 then 5 μM 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 structures after 6 weeks of culture at 26 ± 1°C. Efficiency in embryogenic response of genotypes differed, Kurkaruppan = FR13A > Khao Dawk Mali 105 = Nam Sagui 19 = RD7 > Pin Gaew 56. Additives such as mannitol, 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 α-naphthaleneacetic acid), cytokinins (kinetin and 6-benzylaminopurine) and an ethylene producing chemical (1 -aminocyclopropane carboxylic acid) showed that the plant: growth regulator-free medium or the one supplemented with 1-aminocyclopropane carboxylic acid (5 μM) and kinetin mu 5 μM) were best for plantlet formation. However, a single recommendation could not be made for all cultivars. One further culture modification involving a mild osmotic stress (polyethylene glycol 100 g L^-1) in R-2 liquid medium enhanced plantlet regeneration in Nam Sagui 19 two-fold but Khao Dawk Mali 105 was recalcitrant to this treatment. Plantlets (700) produced from all treatments subsequently developed into plants, most of which were morphologically normal, in the greenhouse.