Agar does not affect in vitro rhizogenesis and ex vitro acclimatization of Handroanthus chrysotrichus

Abstract

The golden trumpet tree Handroanthus chrysotrichus (Bignoniaceae) is an important species, owing to its economic, ecological, medicinal, and ornamental value. However, its production is hindered due to lack of seed availability and viability improved methods of vegetative propagation are needed. Therefore, we evaluated the effect of agar on in vitro rhizogenesis of H. chrysotrichus shoots and the subsequent ex vitro acclimatization of the plants obtained. In the in vitro rhizogenesis assay, we cultured the micropropagated shoots on half-strength nutritive Woody Plant Medium (½WPM) supplemented with 30 g.L-1 sucrose, 50 mg.L-1 myoinositol, 30 cm³ of vermiculite, and one of the three agar concentrations (0, 3.5, or 7 g.L-1), and after 30 d, we assessed the shoots for root production and leaf number. Thereafter, the plants were subjected to a 49-d ex vitro acclimatization period, which consisted of two stages in a growth room and one stage in a greenhouse; we assessed plant survival, leaf number and increases in stem height at the end of each stage. We found that the addition of agar to the growth medium was not necessary to induce adventitious rooting, especially with respect to secondary roots, and that plants grown on medium without agar had the highest number of leaves after acclimatization. Therefore, agar actually hindered both in vitro rhizogenesis and ex vitro acclimatization. The ex vitro acclimatization result in high survival and resumption of growth and development of H. chrysotrichus micropropagated plants, and this step is not affected by agar on in vitro rhizogenesis.