Organogenesis in cultured petiole explants of Begonia x erythrophylla: The timing and specificity of the inductive stimuli

Caulogenesis and rhizogenesis were studied in cultured petiole explants of Begonia x erythrophylla in order to link the developmental stages of primordia initiation with the physiological requirements of the explant, Petiole sections excised from B. x erythrophylla plants grown in vitro, were highly organogenic, with shoots and roots arising directly from cells of epidermal origin, Epidermal cells associated with glandular hairs appeared to be most responsive to organogenic stimuli, The point of explant determination for each form of organogenesis was ascertained by media transfer experiments, Explants became determined for caulogenesis after 7 d exposure to shoot-inducing medium (SIM), while requiring 3 d on root-inducing medium (RIM) for determination, Explants were strongly canalized for caulogenesis once determined, but 5 d on RIM were required before becoming strongly canalized for rhizogenesis, No organ specific differentiation was observed at the point of determination for explants exposed to either shoot- or root-inducing conditions, Preculture on a basal medium containing no growth regulators resulted in a gradual loss of competence with time, but preculture for up to 2 d on SIM or RIM resulted in a reduction in the time for determination for both forms of organogenesis.