Indução de florescimento in vitro de Cattleya walkeriana

Abstract

Cattleya L. orchids are highly appreciated for their variety of colors, shapes, and sizes of their flowers, but they have a long juvenile period. Using mechanisms that accelerate the flowering process is desirable for the market, but knowledge of the phenomena involved in this process is incipient. In this sense, the aim of this study was to investigate the physiological and biochemical behavior of Cattleya walkeriana G. in response to environmental factors (experiment i), light quality (experiment ii), and gibberellin inhibitor (experiment iii), in inducing in vitro flowering. Plants originating from in vitro seeding were subjected to the following experimental conditions: (i) after 6 months of cultivation, they were transferred to different conditions of temperature (26°C, 24°C, 20.5°C, and 17°C), photoperiod (10, 12, 14, and 16 h), and water availability (simulated with different agar doses: 0, 2.75, 5.50, 8.25, and 11 g L-1), and evaluated after 3 months; (ii) after 12 months of in vitro cultivation, they were transferred to different colors of light (red, blue, purple (simulated by 2 reds : 1 blue), and white), provided by light-emitting diodes (LEDs), and evaluated after 6 months; and (iii) after 6 months of cultivation, they were transferred to media with different concentrations of paclobutrazol (PBZ) at concentrations of 0, 0.025, 0.05, 0.075, and 0.1 mg L-1, and evaluated after 3 months. In all three experiments, growth parameters, photosynthetic apparatus, antioxidant metabolism, and carbohydrate metabolism were analyzed. Regarding the environmental factors studied, it was observed that an average temperature of 26ºC, a photoperiod of 12 to 14 hours of light, and 0 mg L-1 of agar promote more expressive growth for the species. White lighting provided greater vegetative growth and greater accumulation of H2O2, understood as a growth signal in this condition, while purple lighting provided greater formation of chlorophylls a, b, and total, and carotenoids, as well as equivalent accumulation of total soluble sugars. However, red, blue, purple, and white LED lighting can be used without damage to the species. PBZ reduced the number of leaves and roots of the species, as well as root length. Additionally, it promoted the increase of shoot, carbon accumulation, and elevation of concentrations of superoxide dismutase, total soluble sugars, reducing sugars, and proteins. The concentration of 0.1 mg L-1 of PBZ can be used for in vitro maintenance of the species. Finally, the species was not responsive to the studied factors for in vitro flowering.