CALLUS INDUCTION AND PLANT-REGENERATION OF US RICE GENOTYPES AS AFFECTED BY MEDIUM CONSTITUENTS

This study was conducted to establish and optimize a regeneration syst em for adapted U.S. rice genotypes including three commercial rice cul tivars (LaGrue, Katy, and Alan) and two Arkansas breeding lines. Facto rs evaluated in the study were genotype, sugar type, and phytohormone concentration. The system consisted of two phases, callus induction an d plant regeneration. In the callus induction phase, mature caryopses were cultured on MS medium containing either 1% sucrose combined with 3% sorbitol or 4% sucrose alone, and 0.5 to 4 mg . L(-1) (2.26 to 18.1 0 mu M) 2,4-D with or without 0.5 mg . L(-1) (2.32 mu M) kinetin. In t he plant regeneration phase, callus was transferred to 2,4-D-free MS m edium containing 0 or 2 mg . L(-1) (9.29 mu M) kinetin combined with 0 or 0.1 mg . L(-1) (0.54 mu M) NAA. Callus induction commenced within a week, independent of the treatments. Callus growth and plant regener ation, however, were significantly influenced by interactions among ex perimental factors. Generally, the greatest callus growth and plant re generation were obtained with 0.5 mg . L(-1) (2.26 mu M) 2,4-D and dec reased with increasing 2,4-D concentrations. Kinetin enhanced callus g rowth only when combined with 0.5 mg . L(-1) (2.26 mu M) 2,4-D, and 4% sucrose. Inducing callus on kinetin-containing medium generally enhan ced regeneration capacity in the presence of sucrose but not with a su crose/sorbitol combination. Media containing sucrose alone generally s upported more callus proliferation, but the sucrose/sorbitol combinati on improved regeneration of some cultivars. NAA and kinetin had little effect on regeneration.