ABSTRACT.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.Keywords: activated charcoal, graphite, orchids, micropropagation.Carvão ativado e grafite para a micropropagação de Cattleya bicolor Lindl. e um duplo híbrido de orquídea 'BLC Pastoral Innocence' RESUMO. Nenhum estudo prévio tem investigado o uso de grafite como substituto do carvão ativado em orquídeas. No presente trabalho, concentrações diferentes de carvão ativado ou de grafite foram adicionadas ao meio KC para escurecer o meio de cultura e estimular a propagação in vitro de Cattleya bicolor e de um duplo híbrido de orquídea ('BLC Pastoral Innocence'). As plântulas foram inoculadas em meio KC sem reguladores de crescimento; os efeitos de concentrações de carvão ativado (0,0; 1,5; 3,0; 4,5; 6,0 and 7,5 g L -1 ) e de grafite (0,0; 1,5; 3,0; 4,5; 6,0 and 7,5 g L -1 ) foram testados separadamente. Foram inoculadas quinze plântulas em cada frasco e os experimentos foram conduzidos sob esquema de planejamento fatorial com dois fatores: meios de cultura e luminosidade; o meio de cultura com onze níveis (diferentes concentrações de grafite ou de carvão ativado) e luminosidade com dois níveis (fotoperíodo de 14h e iluminação contínua). Para cada combinação do nível fatorial foram feitas três repetições. Após seis meses de cultivo, foram registrados os números médios de brotos e raízes induzidos em cada concentração de carvão ativado e de grafite. O maior número de...

ABSTRACT. In the current study, complex (coconut water and ripe-banana pulp) and specific (micronutrients, peptone and activated charcoal) supplements were added to Knudson-C medium (KC) medium to stimulate the in vitro propagation of Hadrolaelia purpurata (=Laelia purpurata) and Encyclia randii orchid species. The highest number of H. purpurata seedlings occurred in KC medium containing 90 g L -1banana pulp maintained with 24-hour illumination. Positive effects of the banana pulp addition in KC medium were reported for the formation of seedlings and leaves from E. randii seeds. The seedling number from seeds of E. randii maintained with continuous illumination was also high in KC medium containing coconut water. Positive effects due to the addition of peptone were reported only in the case of seedling formation from E. randii seeds maintained under continuous illumination. The highest number of H. purpurata seedlings and leaves of E. randii occurred in cultures maintained in continuous illumination. The successful asymbiotic germination of the three-year-old seeds of two Brazilian native species from different regions at reduced costs offers an opportunity for the use of the techniques in commercial nurseries and for ex situ conservation of the native and explored orchid species.