Fontes de nitrogênio no crescimento in vitro de plântulas de Cattleya loddigesii Lindl. (Orchidaceae)

Abstract

This work aimed to evaluate the effect of different concentrations of calcium and ammonium nitrate on the in vitro development of orchids. Cattleya loddigesiiorchid plantlets, 1.0 cm in size produced by self pollinization and also by in vitro germinated seeds, were inoculated in flasks containing 60 mL of WPM culture medium, modified with different concentrations of calcium nitrate (0, 278, 556, 834 and 1112 mg L-1) and ammonium nitrate (0, 200, 400, 600 and 800 mg L-1). The culture medium was supplemented with 20 g L-1 of sucrose, 150 g L-1 of ‘nanica’ banana pulp, activated charcoal 2 g L-1, solidified with agar 6 g L-1, and pH adjusted to 5.7 ± 0.1 before being autoclaved at 121ºC, 1.5 atm pressure during 20 minutes. After inoculations, the flasks were transferred to a growth room with controlled temperature around 25 ± 2ºC, 16h photoperiod regime, with a light intensity of 35 μmol m-2 s-1. After 90 days, it was observed that the best results in terms of number of leaves was achieved with 400 mg L-1 of ammonium nitrate, and the highest number of sprouts was obtained with 450 mg L-1 of ammonium nitrate, but the major number of roots was verified in the treatment with 600 mg L-1 of ammonium nitrate and 278 mg L-1 of calcium nitrate. In resume, it is recommended to use the WPM medium in its original composition, without calcium nitrate to micropropagate C. loddigesii orchid plantlets.