An efficient protocol for micropropagation of Melaleuca alternifolia Cheel

Melaleuca alternifolia is cultivated for the production of an essential oil useful in the cosmetic and pharmaceutical industries. Despite the economic importance of this species, there is little knowledge about its in vitro propagation. The aim of this study was to establish an efficient protocol for micropropagation of M. alternifolia. With the goal of in vitro multiplication by axillary shoot proliferation, both solid and liquid MS and WPM media were tested with supplementation with BA at 0, 0.55, 1.11, 2.22, 3.33, and 4.44 mu M. The best result for shoot multiplication was obtained when either 0.55 mu M BA was added into solid MS medium or 1.11 mu M BA was added into liquid MS medium, with 5.6 and 11.8 shoots per explant generated, respectively. On solid or liquid WPM medium supplemented with 0.55 mu M BA, the proliferation rates were 5.5 and 4.7, respectively. Three auxins (NAA, IAA, and IBA) were tested at 0.53 and 2.64 mu M during the rooting stage. Several sucrose concentrations (15, 30, and 45 g L-1) were compared to a sucrose-free medium. Rooting performances on four culture media were then compared: MS, half-strength MS (MS/2), MS + activated charcoal (AC), and MS/2 + AC. The results showed that auxin addition to culture medium is not necessary for in vitro rooting. Rooted microcuttings from different culture media were acclimatized in a greenhouse, and the survival percentage was evaluated. All shoots cultured in an auxin-free MS medium supplemented with sucrose (30 g L-1) produced roots, and all plants survived during acclimatization. Activated charcoal added in rooting medium reduced rooting rates.