Conservação in vitro por crescimento lento de mangabeira do Cerrado (Hancornia speciosa Gomes)

Abstract

The mangaba is an important fruit tree for the Northeast and Central West regions, because it ensures sustenance and provides food for thousands of extractive families. However its natural areas are located in some of the country’s regions of the greatest anthropization and, currently, the species is threatened with extinction, what justifies the achievement of studies that can result in strategies for its conservation. The objective of this work was to accomplish the in vitro conservation of mangaba by the slow growth technique. The work was conducted at the Biotechnology Laboratory of the University of Uberlândia. For the in vitro establishment, mangaba seeds were disinfested with 70% alcohol and 2.5% sodium hypochlorite for 1 and 30 minutes, respectively, and rinsed with distilled and autoclaved water. Afterwards, they were inoculated in glass jars, sealed with plastic lids, containing 40 mL of MS medium supplemented with 2 g L"1 of activated charcoal, 7 g L"1 of agar and pH of 5.7, which were kept at a temperature of 25°C and photoperiod of 16 hours of light provided by 20 W white fluorescent light bulbs. For the in vitro conservation were made three experiments in which the nodal segments were extracted from plants germinated in vitro and inoculated in MS medium with 7 g L"1 of agar, differing in the following way: the first one tested the effect of osmotic agents and doses (15, 20 and 25 g L"1 of mannitol and 10, 20 and 40 g L"1 of sorbitol) plus one control; the second one, four concentrations of sucrose (0, 10, 20 and 30 g L"1) and two of abscisic acid (0 and 0.5 mg L"1); and the third one, four culture media (100% MS, 50% MS, 100% WPM and 50% WPM) and two temperatures (25 and 20°C). Beyond that, the first two experiments were repeated with the addition of 2 g L"1 of activated charcoal to the conservation medium to compare with the results obtained in its absence. At 45 and 90 days of conservation the survival rate and the number of green leaves of the explants were observed. For growth recovery, the explants were transferred to MS medium containing 7 g L"1 of agar, 1 mg L"1 of BAP, 1 mg L"1 of NAA e 2 g L"1 of activated charcoal. At 60 days were verified the survival rate, number of green leaves, number of nodes, shoot length and fresh mass of nodal segments of mangaba. The results showed that the use of 2 g L"1 of activated charcoal improves the survival and development of the explants. There was a reduction in growth, but low survival rates, when was used: the mannitol in the presence of charcoal; 0.5 mg L"1 of ABA, in the absence of this supplement; and low concentrations of sucrose, regardless of the use of activated charcoal. Explants conserved in 50% WPM medium and temperature of 20°C exhibit low metabolism and a good response to growth recovery stage.