The dedifferentiation and redifferentiation ability of tissues of young rice
panicles in culture was studied with the explants at various ploidy levels.
The purpose of this study was to provide a theoretical basis for increasing
the fequency of callus induction and redifferentiation in the culture of young
rice panicles, and to speed up the propagation of selected materials by
vegetative cloning.
Materials used were diploid, triploid, and tetraploid strains of a rice cultivar, Guangluai 4, and an O. sativa cv. Ewan 3 x O. latifolia F\1\ plant which was an allo-triploid.
The developmental stages of rice panicles were classified into: 1. First bract differentiation; 2. Primary branchlet differentiation; 3. Secondary branchlet and spikelet primordia differentiation; 4. Stamen and pistil differentiation; 5. Pollen mother cell differentiation; 6. Meiosis; and 7. Pollen development. For sterilization, the materials were immersed in 70% alcohol and in 0.1% mercuirc chloride solution for 10 minutes, and were then washed with aseptic water 3 to 5 times. The N6 medium containing 2 mg/l of 2,4-D, 4.5% sucrose and 0.8% agar was used for callus induction, and the MS medium containing 0.5 mg/l of NAA, 2 mg/l KT, 3% sucrose and 0.8% agar was used for differentiation.
The frequency of callus induction and redifferentiation differed greatly according to the developmental stage of panicles. It was highest at the 3rd stage, at which secondary branchlets and spikelet primordia are differentiated. In this respect, there was no significant difference between the ploidy levels. The frequency of callus induction remained high at the 4th stage, and tended to decline at the 5th stage. At the meiotic stage, the ability of regeneration was completely lost. The frequency of albinos in the cultured progenies was 4.7% in 2n, 0.8% in 3n, zero in 4n, and 22.0% in the allotriploid.