Influência do déficit hídrico na germinação de sementes e no desenvolvimento inicial de três espécies de Pleurothallidinae (Orchidaceae)

Abstract

The subtribe Pleurothallidinae has about 4,100 species in 36 genera, and occurs only in the Americas. Acianthera teres (Lindl.) Borba is rupicolous, exposed to light and high temperatures. Octomeria gracilis Lood. ex Lindl. and Octomeria crassifolia Lindl. are epiphytes in forests, but the first grows in moist and the latter in drier areas. The availability of water influences the metabolism at different stages of plant growth. The objective of this study was to evaluate the influence of water deficit induced by the addition of polyethylene glycol 6000 (PEG) to the culture medium, in the germination and initial development of A. teres, O. crassifolia and O. gracilis. Seeds were sown on MS/2 medium under four treatments: control (without PEG), and with 50 g L -1, 100 g L -1 and 200 g L -1 of PEG, inducing water potentials of -0.53, -0.70, -0.86 and -1.60 MPa, respectively. Observations were carried out at 45, 120 and 180 days. In A. teres the lower the water potential of the medium, the lower the germination rate, and the greater the delay in seedling development. In O. crassifolia, the lower the water potential of the medium, the higher the rate of germination, but the development almost equaled between treatments in 180 days. Octomeria gracilis has some tolerance to reduced water potential up to 120 days and grows faster with water potentials of -0.53 and -0.70 MPa.