Influência da qualidade de luz na micropropagação de Eucalyptus dunnii e Eucalyptus grandis × Eeucalyptus urophylla

Abstract

Biotechnological tools, such as tissue culture, especially the micropropagation technique, have enabled large-scale propagation of Eucalyptus species and hybrids with high economic value. However, one of the greatest difficulties of reproducibility of in vitro culture protocols is related to environmental factors. Light, being fundamental for chlorophyll plants, has characteristics such as spectrum quality (wavelength) that can influence in vitro growth and development, a process known as photomorphogenesis. Based on the above, the present work had the objective of evaluating the photomorphogenic effect of six light spectra (red, white, blue, yellow, purple, and green) in the multiplication, elongation and in vitro rooting stages of Eucalyptus dunnii and Eucalyptus grandis × Eucalyptus urophylla (urograndis eucalypt). The wavelengths were provided by filtering the light from fluorescent lamps with double sheets of colored cellophanes. The morphological aspects of shoot length, number of shoots, oxidation of explants, rooting and survival percentage, root length and number, variations in the concentration of photosynthetic pigments and changes in histological organization were evaluated during in vitro culture stages of the foliar tissues. The experiment was conducted in a 2×6 factorial arrangement, in a completely randomized design, with two species and six light spectra being tested. In general terms, the light quality influenced the in vitro photomorphogenesis of the two species studied, where white, red, blue and purple light spectra resulted in the best responses for the analyzed morphological characteristics and the photosynthetic pigments. With the histological analyzes it was possible to verify differences in the organization and thickness of the cells of the foliar tissues among the light qualities tested. The lowest values for stomata size and stomatal density of urograndis eucalypt were observed in green and red-light filters respectively, and in E. dunnii these characteristics were observed in fluorescent white light and green light filter. Thus, the results of this work contribute with relevant information for the in vitro culture of these species and for the understanding of the morphophysiological changes caused by the light quality.