-(Growth of red and green strains of the tropical agarophyte Gracilaria cornea J. Agardh (Gracilariales, Rhodophyta) in laboratory). Gracilaria cornea J. Agardh is an important agarophyte occurring in the western Atlantic Ocean. Green colour individuals of G. cornea were found in a natural population, growing next to red individuals, which were more common. Due to the importance of colour strains in genetic and intraspecific variability studies, this work aimed to characterize the red and green strains evaluating different nutritional and light conditions. Red and green gametophytes were cultivated at 14:10 light: dark cycle, with alternating aeration periods of 30 min. Two different enriched solutions were tested: von Stosch (VSS) at concentrations reduced to 12.5% and 25%; and Provasoli (PES) at concentrations reduced to 25% and 50%, and 100%. Red and green gametophytes were cultivated at the irradiance of 45 µmol photons m -2 s -1 . In another experiment utilizing PES 100%, two sources of light (Osram 40 W daylight fluorescent tubes and Sylvania Designer 3,500 tubes) were tested at irradiances of 90 and 180 µmol photons m -2 s -1. Growth rates (GR) were evaluated for five weeks. Gametophytes developed few branches and reproductive structures were not induced. Differences were not observed between GR of red and green strains in the conditions tested. GR were higher in VSS 12.5% (8.4% day -1 ) than in 25% (7.1% day -1 ), suggesting an adaptation of the species to low nutrient concentrations. GR were higher at 180 (9.0% day -1 ) than at 90 µmol photons m -2 s -1 (6.3% day -1 ). These results suggest that G. cornea should be cultivated in laboratory at high irradiances and low nutrient concentrations. These data will be useful in future genetic and physiological studies of the species.Key words -agarophyte, colour strain, Gracilaria cornea, growth, light RESUMO -(Crescimento de linhagens de coloração verde e vermelha da agarófita tropical Gracilaria cornea J. Agardh (Gracilariales, Rhodophyta) em laboratório). Gracilaria cornea J. Agardh é uma importante agarófita que ocorre no Oeste do Oceano Atlântico. Indivíduos de coloração verde de G. cornea foram encontrados em uma população natural, próximos a indivíduos de coloração vermelha, mais comuns. Devido à importância de linhagens cromáticas em estudos de genética e variabilidade intraespecífica, o objetivo deste trabalho foi caracterizar as linhagens verde e vermelha avaliando diferentes condições de nutrintes e luz. Gametófitos verdes e vermelhos foram cultivados em fotoperíodo de 14 horas (14L:10E), com períodos alternados de aeração de 30 minutos. Duas soluções de água do mar enriquecida foram testadas: von Stosch (VSS) nas concentrações reduzidas a 12,5% e 25%; e Provasoli (PES) nas concentrações reduzidas de 25% e 50%, e 100%. A irradiância foi de 45 µmol fótons m -2 s -1 . Num outro experimento, utilizando-se PES 100%, dois tipos de fontes luminosas (lâmpadas fluorescentes Osram 40 W luz do dia e Sylvania Designer 3.500) foram testadas em duas irra...
