No previous studies have investigated the use of graphite instead of activated charcoal in orchids. In this work, different concentrations of activated charcoal or graphite were added to KC medium to darken the culture medium and stimulate the in vitro propagation of Cattleya bicolor and of a double hybrid orchid ('BLC Pastoral Innocence'). The seedlings were inoculated on growth regulator-free KC medium; the effects of activated charcoal (0.0, 1.5, 3.0, 4.5, 6.0, and 7.5 g L-1) and graphite (0.0, 1.5, 3.0, 4.5, 6.0, and 7.5 g L-1) concentrations were tested separately. Each flask contained fifteen seedlings, and the experiments had a randomised, two-way factorial design. The two tested variables were culture medium and illumination levels; eleven culture levels (different concentrations of graphite or activate charcoal) and two illumination levels (14-hr photoperiod or continuous illumination) were evaluated. Three replicates of each combination were utilised. After six months of culture, the average numbers of induced buds and roots per seedling were recorded for each concentration of activated charcoal or graphite. Whereas the largest number of buds in C. bicolor seedlings occurred on media containing 6.0 or 7.5 g L-1 graphite, the largest number of roots occurred on media containing 6.0 g L-1 activated charcoal. In the hybrid 'BLC Pastoral Innocence', the largest number of buds and roots was reported in medium with 4.5 g L-1 activated charcoal. When using graphite in place of activated charcoal, we obtained disparate the results in root formation that suggest that graphite is not a recommended substitute for activated charcoal.
activated charcoal; graphite; orchids; micropropagation
