Influence of light and temperature on seed germination of Cereus pernambucensis Lemaire (Cactaceae)

Abstract

TAKAKI, M. Influence of light and temperature on seed germination of Cereus pernambucensis Lemaire (Cactaceae). Biota Neotrop. 10(2): http://www.biotaneotropica. org.br/v10n2/en/abstract?article+bn00710022010. Abstract:The objective of the present study was to evaluate the effects of light and temperature on germination of Cereus pernambucensis seeds, a species of columnar cactus native to Brazil and naturally incident in the restinga. Cereus pernambucensis seeds were incubated under different temperatures, from 5 to 45 °C, with 5 °C intervals, and under alternating temperatures of 15-20 °C, 15-30 °C, 20-25 °C, 20-30 °C, 20-35 °C, 25-30 °C, 25-35 °C, and 30-35 °C, both under Resumo: Este estudo teve como objetivos avaliar os efeitos da luz e da temperatura na germinação de sementes de Cereus pernambucensis, espécie de cacto colunar, nativa do Brasil que ocorre naturalmente na restinga. As sementes foram incubadas sob diferentes isotermas, entre 5 e 45 °C, com intervalos de 5 °C, e sob termoperíodos de 15-20 °C, 15-30 °C, 20-25 °C, 20-30 °C, 20-35 °C, 25-30 °C, 25-35 °C, 30-35 °C, ambos na presença e ausência de luz contínua. As sementes também foram submetidas a um gradiente de fotoequilíbrio do fitocromo a 25 °C. A temperatura ótima para a germinação desta espécie está entre 25 e 30 °C. A alternância de temperatura não alterou a porcentagem de sementes germinadas, porém observaram-se alterações na velocidade e índice de sincronização. As sementes incubadas no escuro não germinaram em qualquer das condições testadas, indicando que a espécie, quando em condições de cultivo, é fotoblástica positiva. As sementes apresentam tolerância a diversas condições de sombreamento, germinando em condições de fluência muito baixa. Palavras-chave: cacto colunar, Cereus pernambucensis, restinga. Mancinelli (1994).For germination experiments, 50 mm diameter Petri dishes lined with two sheets of filter paper were used throughout. Each treatment contained four replicates of thirty seeds. Eight treatments of different temperatures at 5 °C intervals from 5 to 45 °C were used to evaluate the effect of different isotherms under white light or dark on germination. The effect of the 12 hours thermal period on germination was tested with the following pairs of alternating temperatures: 15-20 °C, 15-30 °C, 20-25 °C, 20-30 °C, 20-35 °C, 25-30 °C, 25-35 °C and 30-35 °C under light and dark. Temperatures and thermal periods that did not allow germination twenty days after the beginning of the experiments were excluded from statistical analyses. The white light was obtained from two fluorescent daylight type 15W light bulbs (32.85 µmol.m -1 /s). Petri dishes were inserted inside a colorless gerbox container for the experiments in light and a black gerbox container for those in the dark. The seeds under dark condition were monitored with a green safety light (Amaral-Baroli & Takaki 2001).Seeds that presented a primary root with at least 1mm were considered as germinated. Experiments were monitored daily with counting and removal of germi...

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