Microalgas, sistemas de micropropagação e diodos emissores de luz na germinação e desenvolvimento inicial in vitro de Cattleya nobilior Rchb.f.

Abstract

The Orchidaceae family, due to habitat destruction, climate change, and illegal extraction, is vulnerable, with many species threatened with extinction, making the conservation and multiplication of native species, such as Cattleya nobilior, a necessity. Biotechnological tools, such as in vitro culture, emerge as strategies for the efficient propagation of these species. This study developed and optimized in vitro culture protocols for C. nobilior through two distinct but complementary experiments. The first experiment evaluated the effect of different concentrations of the microalga Chlorella sp. (0; 1.5; 3.0; 4.5 g L-1) and two LED irradiance levels (18 and 36 µmol m-2 s-1), in a 4 x 2 factorial design. The second experiment compared three micropropagation systems (heterotrophic, photoautotrophic, and photomixotrophic), under the same two LED irradiance levels (18 and 36 µmol m-2 s-1), in a 3x2 factorial design. Both experiments, conducted in solidified Murashige & Skoog medium under controlled temperature and photoperiod conditions (25 ± 2 °C; 16 h), assessed the survival, germination percentage, and developmental stages of the propagules at 60 and 120 days (Experiment 1) and 45 and 90 days (Experiment 2). Data were subjected to analysis of variance and means compared by Tukey's test (p<0,05), using the SISVAR software. Results from the first experiment indicated that the irradiance of 36 µmol m-2 s-1 was more influential than microalgae supplementation for propagule development, with the highest percentage of P4 stage plantlets (97.60%) observed in the control treatment under this irradiance at 120 days. For the second experiment, the photomixotrophic micropropagation system and 36 µmol m-2 s-1 irradiance were more favorable, promoting 100% germination at 45 days and 43.85% of P4 stage plantlets at 90 days. The optimization of these factors contributed to accelerating reproduction and promoting sustainable practices, aiding in the conservation of the species and reducing illegal harvesting. Thus, the use of irradiance of 36 µmol m-2 s-1 accelerated the development of C. nobilior propagules in both experiments, being suitable for their germination and in vitro cultivation in growth chambers, since it is a species that occurs in the Cerrado strictu sensu.