Effect of microalgae Messastrum gracile and Chlorella vulgaris on the in vitro propagation of orchid Cattleya labiata

Abstract

The aim of this study was to evaluate the effect of two green microalgae (Messastrum gracile and Chlorella vulgaris) in comparison with plant growth regulators (6-benzylaminopurine, BAP; thidiazuron, TDZ; zeatin, ZEA) on the in vitro propagation of Cattleya labiata, an endangered orchid, using the thin cell layer (TCL) technique from protocorms. TCL sections were cultivated in MS/2 medium containing M. gracile extract (EM) and biomass (BM); C. vulgaris extract (EC) and biomass (BC); and BAP, TDZ, and ZEA in different concentrations. Subsequently, the explants were grown in MS/2 medium, with 2 g L−1 of activated charcoal, to induce elongation and roots formation. For acclimatization, plants were transplanted in trays using Sphagnum sp. as substrate. TCL explants showed a higher formation of protocorm-like bodies (PLBs) than entire protocorms. Explants cultivated in media supplemented with BM showed a high rate of PLB regeneration (59%) and high mean number of PLBs (4 per explant) and 85% survival after acclimatization of the plants. Supplementation with BAP stimulated similar morphogenic responses to those observed with BM and superior results obtained with ZEA and TDZ. Mass propagation of C. labiata plants was successfully achieved using TCL, and it is recommended to supplement the MS/2 medium with 4 g L−1 of BM or 4 mg L−1 of BAP. Microalgae extracts and biomasses are effective alternatives for in vitro propagation of C. labiata that can replace plant growth regulators, as they favored the formation of PLBs and plants.