Production of high-Quality Ornithogalum thyrsoides cut flowers in one year from in vitro propagated plantlets influenced by plant growth regulators

Abstract

The objective of this study was to investigate the optimum concentration of plant growth regulators for explants cultured in vitro to produce inflorescences of Ornithogalum thyrsoides ‘Chesapeake Starlight’ forcing directly from in vitro propagules in one year. Two sizes of explants (2 × 2 and 2 × 4 mm) were cultured on a Murashige and Skoog (MS) medium supplemented with 0, 1.35, 2.7, or 5.4 μM 2-(1-Naphthyl)acetic acid (NAA) and with 0, 3.3, 6.6, or 13.2 μM N-(phenylmethyl)-7H-purin-6-amine (BA); and with 0, 0.675, 1.35, or 2.7 μM NAA and with 0, 2.2, 4.4, or 8.8 μM BA at 21 °C. Explants propagated in a Petri dish were directly transplanted to 6.3 cm pots as a clump without separating plantlets from the explant (propagule), then transplanted to a tray, and forced at 16.5/16 °C (day/night). The number of days to flowering from the first and second scape (FS and SS, respectively) from the first, second, or third plantlets (FP, SP, and TP, respectively) formed from the clump of one explant was counted from the date of transplanting to pots, and scape length and diameter were recorded. Criteria for high-quality cut flowers were (1) flowering around 200–215 days in FS/FP and 230–245 days in SS/FP with a flowering rate of 90–100% in FS/FP and 70–80% in SS/FP, (2) a scape length greater than 50 cm in FS/FP and greater than 55 cm in SS/FP, and (3) a scape diameter above 8 mm. Based on these criteria, the optimum concentrations of NAA and BA were determined. High quality O. thyrsoides cut flowers flowering after 195–201 days, a flowering rate of 78–100% in FS/FP, and three or four scapes of SS/FP and FS/SP can be successfully produced from 2 × 2 mm or 2 × 4 mm explants cultured in MS medium supplemented with 1.35–2.7 μM NAA and 4.4–6.6 μM BA. This demonstrates that quality cut flowers can be produced in less than one year without separating plantlets grown in vitro as one clump which saves labor. Developing two scapes from each of two first plantlets may suggest competition for reserves of metabolites/endogenous plant hormones.