Propagação in vitro de Cattleya Lindl. (Orchidaceae) nativas do cerrado brasileiro em função da luz

Abstract

In vitro cultivation is a valuable biotechnological tool in obtaining plants both for commercial cultivation and for research aimed at the preservation of species. Among them stand out Cattleya nobilior Rchb.f., and Cattleya walkeriana Gardner that belong to the Orchidaceae family. These plants are native to Brazil and are classified as near endangered and vulnerable, respectively. Thus, protocols for the in vitro technique vary depending on the species to be produced, thus making it necessary to adapt the procedure to each one of them. The objective of this work was to determine a methodology for the tetrazolium test, germination and the initial in vitro development of propagules of two orchids of the genus Cattleya native to the Brazilian Cerrado. Three independent experiments were carried out in the In vitro Cultivation Laboratory of the Faculty of Agricultural Sciences, Federal University of Grande Dourados-UFGD. For the first experiment, the objective was to identify an adequate methodology to identify the viability of Cattleya seeds by the tetrazolium test, through three pre-conditioning: without imbibition (control); sucrose (10%) or distilled water and, after 24 hours, submitted to a tetrazolium solution, with three types of conditioning: oven (40 °C), water bath (40 °C) or room temperature. After this 24-hour period, the percentage of viable seeds (%SV) was calculated and at 45 days after sowing, the germination percentage (%G) at the characterization level was calculated. The second experiment aimed to evaluate the in vitro germination and initial development of orchids of the genus Cattleya Lindl. natives of the Brazilian Cerrado as a function of the light spectrum. After sowing, cultures were placed under the following light spectra - L1: 100% white LED (6,500K); L2: 100% red LED; L3: 100% blue LED; L4: 50% blue + 50% red LED; L5: LED 50% white + 25% blue + 25% red; L6: LED 75% blue + 25% red; L7: LED 75% red + 25% blue and L8: white fluorescent lamp (6,500K). At 45 and 90 days after sowing, the germination percentage (%G) and the initial establishment of the propagules were evaluated. Regarding the third experiment, the objective was to evaluate the in vitro germination and initial development of orchids of the genus Cattleya Lindl. natives of the Brazilian Cerrado due to natural and artificial light sources. After inoculation, the vials were placed under the following light sources - L1: 3,000K yellow LED (128 µmol m-2 s -1 ); L2: 6,500K white LED (108 µmol m-2 s -1 ); L3: 6,500K white fluorescent lamp (23 µmol m-2 s -1 ) and L4: natural light - 35 µmol m-2 s -1 . After 45 and 90 days after sowing, the germination percentage (%G) and the initial establishment of the propagules were evaluated. For experiment I, the species C. nobilior and C. walkeriana, native to the Cerrado, the conditioning at room temperature had a greater effect on the visualization of seeds, suggesting that the tetrazolium test should be performed at this conditioning temperature. For experiment II, light spectra such as L5 and L2 can be indicated as substitutes for L8, used in growth rooms. Regarding experiment III, an artificial light source such as L1 can be indicated as a substitute for L3, used in growth rooms in in vitro culture laboratories.