Efficient use of biomass and extract of the microalga Desmodesmus subspicatus (Scenedesmaceae) in asymbiotic seed germination and seedling development of the orchid Cattleya warneri

Abstract

This study evaluated the effect of the addition of biomass and aqueous extract of the green microalga Desmodesmus subspicatus on asymbiotic germination and seedling development in the orchid Cattleya warneri. Seeds were germinated in MS culture medium with the macronutrients reduced by half (MSM/2), supplemented with 0, 0.25, 0.5, 1.0, and 2.0 g L−1 of microalgal biomass or its aqueous extract. Chlorophyllous protocorms were observed at 4 weeks and the addition of biomass or extract (0.25 g L−1) accelerated germination. Twenty-four weeks after sowing high percentages of seedlings (greater than 95%) were observed in all treatments with biomass, as well as with the addition of 0.25 or 0.5 g L−1 of microalgal extract. Shoot elongation and root development were increased in the semi-solid medium supplemented with 2.0 g L−1 of activated charcoal. Plantlets cultivated in a double-phase medium (a thin layer of liquid medium, containing 0.5 to 2 g L−1 of extract on the semi-solid medium) demonstrated the positive effect of zeatin on the formation of new shoots and plants. Plantlets were successfully acclimatized, showing high percentages of survival (over 80%) with foliar sprays of 2.0 g L−1 of biomass or 1.0 g L−1 extract for 4 months. The addition of D. subspicatus biomass or extract accelerated germination, induced shoot formation, and produced well-developed seedlings during acclimatization. A complete and efficient protocol of germination and seedling development of C. warneri was therefore achieved using biomass and aqueous extract of D. subspicatus.