Abstract Cyathea corcovadensis and Cyathea phalerata are tree ferns native to Brazil, endangered in the state of Rio Grande do Sul. Spore germination and gametophyte development in media with different nutrient formulations and activated charcoal were evaluated, aiming to develop a process for obtaining plants of the two species. Spores were sown in four semi-solid culture media: Meyer, Dyer, MS with 50% and MS with 25% of the original macronutrient concentration. For each medium, 10 replicates were carried out (flasks with 5 mg of spores/30 mL of medium), with and without 1% activated charcoal, respectively. Spore germination and gametophytic development (laminar and cordate stages) were quantified at 30, 60 and 90 days of culture. Cyathea corcovadensis and C. phalerata germinated and developed gametophytes in all media. For both species, the highest percentages of germination and cordate gametophytes (more advanced development stage) were recorded in Meyer medium without activated charcoal, which has higher concentrations of macronutrients and no micronutrients compared to the other evaluated media. We recommend cultivating the plants in Meyer medium for greater gametophytic development and subsequent sporophyte obtention, as a biotechnological tool for C. corcovadensis and C. phalerata conservation and for environmental restoration and enrichment using these tree ferns.

Resumo Cyathea corcovadensis e Cyathea phalerata são samambaias arborescentes nativas do Brasil, ameaçadas de extinção no estado do Rio Grande do Sul. A germinação de esporos e o desenvolvimento de gametófitos em meios com diferentes formulações de nutrientes e carvão ativado foram avaliados, visando ao desenvolvimento de um processo para obtenção de plantas das duas espécies. Esporos foram semeados em quatro meios de cultura semi-sólidos: Meyer, Dyer, MS com 50% e MS com 25% da concentração original dos macronutrientes. Para cada meio, foram realizadas 10 repetições (frascos com 5 mg de esporos/30 mL de meio), respectivamente com e sem 1% de carvão ativado. A germinação dos esporos e o desenvolvimento gametofítico (estádios laminar e cordiforme) foram quantificados aos 30, 60 e 90 dias de cultivo. Cyathea corcovadensis e C. phalerata germinaram e desenvolveram gametófitos em todos os meios. Para ambas as espécies, as maiores porcentagens de germinação e de gametófitos cordiformes (estádio de desenvolvimento mais avançado) foram registradas no meio Meyer sem carvão ativado, que se caracteriza por maiores concentrações de macronutrientes e ausência de micronutrientes em comparação com os demais meios avaliados. Recomendamos cultivar as plantas em meio Meyer para maior desenvolvimento gametofítico e subsequente obtenção de esporófitos, como uma ferramenta biotecnológica para a conservação de C. corcovadensis e C. phalerata e restauração e enriquecimento ambiental usando estas samambaias arborescentes.

ABSTRACT In order to successfully establish themselves in their natural environment, ferns need habitats with abiotic conditions that are suitable for spore germination and gametophyte development. The objective of this study was to assess the influence of abiotic factors on the initial development of Cyathea phalerata cultivated in vitro. Spore germination and gametophyte development were assessed under varying conditions of surface sterilization, pH, temperature and photoperiod. Exogenous contamination was eliminated by sterilizing spores with 2.5 % NaClO for 15 min and sowing them into a culture medium supplemented with nystatin. Spores germinated at all pHs tested. Gametophytic development was faster in acidic pHs. Cultures at 25 °C exhibited the highest percentages of germination and laminar gametophytes. The species produced its highest percentages of gametophytes in cultures with photoperiods between 6 and 18 h. The optimal abiotic conditions found here for in vitro development of C. phalerata are similar to those found in its natural habitat. The southern limit of this species to north of the 30th parallel in Rio Grande do Sul, Brazil, may be because further south spores do not encounter the ideal combined conditions of temperature, pH and photoperiod determined in the laboratory.