Thidiazuron induces in vitro inflorescence formation in young transformed Dendrobium Sonia explants on a modified Knudson C medium

Abstract

In transgenic orchids, the effect of a transgene on flower color cannot be scored until the plant flowers, which may take three to five years after transformation. Inducing flowers in vitro would allow for much earlier screening. Therefore, we tested whether plant growth regulators (PGRs) added to a modified Knudson C (modified KC) medium could induce flowering in young-transformed Dendrobium Sonia explants. Five-month-old rootless explants of the DsF3H_RNAi line were grown on modified KC medium supplemented with
6-benzyladenine (BA; 1.0, 2.5, and 5.0 mg L^-1), gibberellic acid (GA₃; 0.1, 1.0, and
5.0 mg L^-1), or thidiazuron (TDZ; 0.1, 0.5, and 1.0 mg L^-1) and observed for nine months. Inflorescences were formed only on the TDZ-supplemented medium. The 0.5 mg L^-1 gave the highest induction rate (30%), whereas 1.0 mg L^-1 TDZ did not induce any inflorescences and left the plants stunted. The inflorescences that formed never produced healthy floral buds and withered soon after emerging. The application of BA strongly promoted shoot formation, and GA₃ promoted root regrowth, whereas TDZ-treated plants had short leaves, long internodes, and few or no roots. A low concentration of TDZ in the KC medium is thus sufficient to switch young-transformed Dendrobium Sonia towards flowering, but obtaining fully developed flowers will require further work on medium composition, PGR combinations, temperature, and photoperiod.