Indução de protocormos a partir de calos cultivados in vitro de Cattleya nobilior Rhcb.f. (Orchidaceae)

Abstract

The specie Cattleya nobilior Rhcb.f (Orchidaceae) is an epiphytic plant, found in gallery forests and dry forest of the Cerrado. The plants of this species have great commercial importance due to the beauty of their flowers. Considering the importance of the production of large scale and homogeneous seedlings, the use of in vitro cultivation techniques and the production of seedlings from somatic cells has been a technique and tool for this purpose. In this sense, this work was developed with the purpose of evaluating the callus differentiation in protocorms in vitro culture. To achieve the proposed goal, callus masses (explants) obtained from the dedifferentiation of somatic tissues (particularly leaves) were cultured in vitro with different growth regulators added to the culture medium. The treatments consisted of a combination of auxin (indole acetic acid - AIA) and cytokinin (thidiazuron - TDZ), in three concentrations (0 = control, 1.0, 2.0 and 3.0 mg L-1 ), totaling four treatments. At 60 days of culture the fresh and dry masses and the different growth stages of the explants were evaluated: Stage I - undifferentiated callus; Stage II - chlorophyll swollen protocorm; Stage III - protocorm with formation of foliar primordia; and Stage IV - protocorm with developed leaf blades. The means obtained in the different treatments demonstrated that the callus differentiation in C. nobilior protocorms did not show significant differences among the treatments tested, indicating the need for a longer cultivation period and/or low efficiency of the types of growth regulators and concentrations tested. In medium supplemented with 3.0 mg L-1 of AIA combined with 3.0 mg L-1 of TDZ, approximately 97% of the callus remained in stage I. On treatment with 1.0 mg L-1 of AIA + 1.0 mg L-1 of TDZ was observed higher number of explants in stage II (2.94%), whereas, the greater differentiation of callus in protocormos in more advanced stages (III and IV ), as well as the largest fresh and dry masses were verified in explants grown in growth regulator-free medium. Considering the observed results, it is concluded that for Cattleya nobilior, callus cultivation in regulator-free medium promotes greater callus differentiation in protocorms, however, to obtain a higher percentage of differentiation, with microplants with developed leaf blades (stage IV), further studies are needed.