Superação da dormência de sementes e cultivo in vitro de bracatinga (Mimosa scabrella Benth.)

Abstract

Mimosa scabrella Benth. is a tree from Brazil, growing from Minas Gerais to Rio Grande do Sul. Its wood is used for energy like firewood and coal. The round wood is also very sought for props in civil architecture. Furthermore, since it is an aggressive pioneering species, its plantation is recommended for protection and recovering of weak and erosive soil. The Brazilian plantations of Mimosa scabrella Benth. present reduced productivity, which can be improved by the introduction of trees with larger diameter. The increase of the diameter can be obtained by the manipulation of the levels of vegetable hormones in the cells during the micropropagation. Aiming at contributing for this purpose, the overall goal of this work was to study the Mimosa scabrella Benth. in vitro regeneration considering isolated explants from germinated seeds. The surpassing of the seeds' quiescence was tested by mechanical scarification, immersion in water at environment temperature during 24 h, immersion in hot water (80ºC) during 5 minutes. The disinfestation consisted of the immersion of sodium hypochlorite to 2% during 5, 10 or 15 minutes and inoculation of the seeds in ½ MS or MS agent (Murashige & Skoog). Nodal segments cultivated in MS agent added of benzylaminopurine - BAP (0; 2,5; 5; 7,5 and 10 μM) and of alpha-aceticnaphtalene acid - ANA (0 and 2,2 μM), in the absence or in the presence of estreptomicine, were evaluated according to their multiplication in vitro. The mechanical scarification was the quiescence surpassing method which provided the largest germination percentage. The disinfestation with sodium hypochlorite at 2% during 10 minutes resulted in more than 60% of germinated seeds. The biggest in vitro germination of Mimosa scabrella Benth. s seeds was observed at ¼ MS dilution. In the absence of BAP, there was more formation of buds (1,39) and of leaves (1,62) per explant. There was not any contamination by bacteria in the absence of BAP, independently of the presence of estreptomicine. Calli were not formed in the absence of estreptomicine and of BAP. With the increase of BAP concentrations at the medium of culture, there was a reduction in the fenolic oxidation. For the in vitro multiplication of nodal segments of Mimosa scabrella Benth., it is not necessary to add either ANA or BAP.