CALLOGENESIS AND RHIZOGENESIS IN MAHOGANY (Swietenia macrophylla King) EXPLANTS CULTURED in vitro

Abstract

The indiscriminate exploitation of tropical trees in a search for economically valuable species leads to the risk of extinction of several species. This is the case of mahogany (Swietenia macrophylla King) in Brazil. The establishment of a method of direct or indirect bud regeneration could help to produce a great number of plantlets and could constitute an alternative to sexual propagation. The latter is limited by the fact that mahogany seeds lose their germinative power soon after harvest. In this work, two kinds of explants were used: leaf and root fragments from in vitro cultured plants. After disinfection, the explants were cultured in petri dishes containing modified Murashige and Skoog (1962) culture medium, with three-quarters of salt concentration, vitamins, 30 g.L^-1 sucrose and 7 g.L^-1 agar. The combinations of growth substances were: naphthaleneacetic acid (ANA 0.11 mM and 0.54 mM) and one type of cytokinin, kinetin (CIN 1.2 mM, 2.3 mM, 4.7 mM and 9.3 mM), 6-benzylaminopurine (BA 2.2 mM, 4.4 mM and 8.8 mM) or 2-isopentenyladenine (2-iP 2.5 mM). The variables were the concentration and combinations of the growth regulators and the explant origin.The cultures were evaluated every 30 days, the number of explants forming calluses or roots was recorded and the callus consistency was observed. Calluses were formed in both kinds of explants. In leaf explants, 90% of explants formed callus when culture medium contained 4.4 mM BA with 0.54 mM ANA and 8.9 mM BA with 0.11 or 0.54 mM ANA. For root explants, the combination that gave the highest number of calluses was 2.2 mM BA and 0.54 mM ANA and 55% of them formed callus. Adventitious roots were regenerated from leaf calluses or directly from leaf lamina cultured in media containing CIN and ANA. However, adventitious buds were not obtained with the growth regulator combinations tested in these experiments.