Investigations on in vitro multiplication and rooting in Camellia japonica L.

To determine optimum conditions for in vitro propagation of Camellia japonica L., apical and axillary buds of 19 Japanese genotypes, and apical shoots of 4 commercial cultivars (‘California’, ‘General Coletti’, ‘Doctor Burnside’ and ‘Charles Cobb’) were respectively placed on half-strength Murashige and Skoog (MS½) and Anderson’s Rhodondendron (AR) multiplication substrates. The first experiment evaluated the effects of 6-benzyladenine (BA, 5 mg L-1), or BA (1 mg L-1) + gibberellic acid (GA3, 1 mg L-1), associated with darkness or 16/8 h photoperiod, at 25°C. In the second trial, after multiplication on AR medium supplemented with BA (1 mg L-1), the explants were placed on AR rooting medium with or without indole-3-butyric acid (IBA, 0.5 and 1 mg L-1), included or not in nanosponge (β-CD-NS 1:4), a novel potential nano-carrier. A further experiment was carried out maintaining the shoots on substrate enriched with IBA, included or not in β-CD-NS 1:4, for 11 days to induce the differentiation of root primordia, then transferred to AR basal medium for subsequent development. In the first study, the most interesting results were obtained in darkness conditions. Axillary buds showed the highest shooting rate (100%) on both substrates, and apical buds the lowest (60%) on BA (5 mg L-1) in 16-h photoperiod. Axillary buds budded earlier (within 2 weeks), but the mortality rate was up to 94.8%, in comparison with the 54% observed in apical buds. Moreover, BA-GA3 (1 mg L-1) substrate induced callus formation in axillary buds that turned dark-brown within 20 days. Browning and necrosis were also denoted in all the other explants, therefore rooting capacity could not be tested. Concerning the second and third experiments, the highest multiplication rates were found in ‘General Coletti’ and ‘Doctor Burnside’ (39 and 34%, respectively), while in ‘California’ and ‘Charles Cobb’ were nearly halved (18 and 19%, respectively). Results highlight a very slow in vitro multiplication and serious difficulties in rooting of camellia.