Thidiazuron-Induced Organogenesis and Somatic Embryogenesis in Sugar Beet (Beta vulgaris L.)

Improved in vitro tissue culture systems are needed to facilitate the application of recombinant DNA technology to the improvement of sugar beet germplasm. The effects of$N^6-benzyladenine (BA)$and thidiazuron (TDZ) pretreatment on adventitious shoot and somatic embryogenesis regeneration were evaluated in a range of sugar beet breeding lines and commercial varieties. Petiole explants showed higher frequencies of direct adventitious shoot formation and produced more shoots per explant than leaf lamina explants. TDZ was more effective than BA for the promotion of shoot formation. The optimal TDZ concentrations were$2.3-4.6 \mu M$for the induction of adventitious shoot regeneration. Direct somatic embryogenesis from intact seedlings could be induced by either BA or TDZ. TDZ-induced somatic embryogenesis occurred on the lower surface of cotyledons at concentrations of$0.5-2 \mu M$and was less genotype-dependent than with BA. A high frequency of callus induction could be obtained from seedlings and leaf explants, but only a few of the calluses derived from leaf explants could regenerate to plants via indirect somatic embryogenesis. These results demonstrated that TDZ could prove to be a more effective cytokinin for in vitro culture of sugar beet than BA. Rapid and efficient regeneration of plants using TDZ may provide a route for the production of transgenic sugar beet following Agrobacterium-mediated transformation.