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Micro-propagation techniques contribute to the multiplication of several bromeliad species. However, micropropagated plantlets often present low survival rate due to anatomical and physiological disorders induced by in vitro conditions. This study aimed to evaluate the sucrose and gas exchange impact on in vitro propagated Billbergia zebrina plants and to check if there is any residual effect of the in vitro conditions on micropropagated plants after acclimatization. Previously in vitro-established B. zebrina plants were transferred to culture media containing 0.0, 15.0, 30.0, 45.0 or 60.0 g L -1 sucrose. Two different culture container sealing systems were tested: lids with a filter (permitting an excellent gas exchange) and a filter covered with PVC (blocking fluent gas exchange). At 45 days in vitro growth, B. zebrina plantlets were transplanted onto plastic pots containing peat and cultivated for 80 days in greenhouse. At 45 days in vitro and 80 days of acclimatization in the greenhouse, the plants were evaluated. High sucrose levels in the in vitro media resulted in reduced growth. Plantlets exposed to aerated containers presented better rooting, being the sugar-free medium the best in vitro condition (photoautotrophic condition). Limited air exchange resulted in plantlets with anatomical and physiological disorders at the end of the in vitro period. The highest growth rate in the greenhouse was observed in plants previously propagated in unlimited gas exchange system and sugar-free medium. The use of photoautotrophic conditions induces B. zebrina plantlets without anatomical and physiological disorders and it interfere positively on ex vitro growth.

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Sucrose, the most commonly used carbon source in conventional in vitro culture, and limited air exchange in the culture containers are factors that affect the growth of in vitro-cultured plants. They may induce physiological disorders and decrease the survival rate of plants after transfer to ex vitro conditions. The aim of the present study was to analyze the effects of gas exchange and sucrose concentration on Billbergia zebrina plantlets during in vitro propagation. In vitro-established B. zebrina plantlets were transferred to culture media containing 0, 15, 30, 45, or 60 g L-1 sucrose. Two different culture-container sealing systems were compared: lids with a filter (permitting gas exchange) and lids with no filter (blocking fluent gas exchange). Carbohydrate and chlorophyll (Chl a+b) concentrations were analyzed in plantlets at 45-days of culture. The addition of sucrose to the medium reduced the Chl a+b concentration in the plantlets. On the other hand, additional sucrose had a positive effect on the carbohydrate stock formation of the plantlets. The results showed that a photoautotrophic system (air exchange and a sugar-free medium) improves the in vitro propagation of B. zebrina without creating physiological disorders.

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