Plant growth and early in vitro floral differentiation of vanilla (Vanilla planifolia Jacks. ex Andrews)

Abstract

Objective: To induce in vitro flowering of vanilla (Vanilla planifolia) with different plant growth regulators (PGRs) using the double-layer technique.

Design/methodology/approach: A layer of semi-solid Knudson C (KC) medium, added with 40 g L^-1 sucrose, 15% coconut water (CW; v/v) and 7 g L^-1 agar, was placed in 100 mL flasks. A liquid layer of the same composition without agar was placed on top. It was supplemented with different doses (mg L^-1) of PGRs: 6-benzyladenine (BA) (7), thidiazuron (TDZ) (6), paclobutrazol (PBZ) (0.5) and gibberellic acid (AG₃) (2). Plus two controls, C1: no PGRs + no CW; C2: no PGRs + CW. Vanilla shoots of 2 cm in length and with at least one axillary shoot were placed. They were incubated at a temperature of 26±2 °C day and 18 °C darkness, with light intensity of 55 µmol m^-2 s^-1 during 13 weeks. The number of shoots, leaves and roots was evaluated, as well as the length of shoots and fresh weight. Floral differentiation was evaluated at the tenth week by conventional microtechnique.

Results: The number shoots and leaves and shoot length were significantly higher in C2. The number of roots increased with PBZ 0.5 mgL^-1. C1 and C2 promoted higher fresh weight. Floral differentiation was observed with AG₃ 2 and PBZ 0.5 mg L^-1 treatments.

Limitations on study/implications: Further evaluation of other PGR doses and environmental conditions is required to achieve full floral differentiation of vanilla.

Findings/conclusions: CW increased vegetative growth. AG₃ and PBZ showed early floral differentiation in Vanilla planifolia, which is the first report of this phenomenon for the species.