Dormência cíclica e parâmetros térmicos para a germinação de sementes de Eriocaulaceae

Abstract

Eriocaulaceae has pantropical distribution, being many species popularly known as "sempre-vivas". The campos rupestres from Espinhaço Range are considered the center of diversification of the group. In these environments, marked by seasonality, dormancy cycles were described for Syngonanthus verticillatus seeds. In this species, typical summer conditions (high humidity and temperature) are associated with the acquisition of dormancy, whereas dormancy overcoming occurs in the dry season. The main of the first chapter was to determine the minimum time required for the acquisition and overcoming of dormancy on wet and dry substrate, respectively, under two temperature regimes (15 and 25°C), and the effect of treatments of drying and application of gibberellin and fluridone (inhibitor of abscisic acid biosynthesis, ABA) to overcome dormancy. The temperature modulates the rate of dormancy acquisition, this process being faster under the highest temperature (25°C). Seed dormancy alleviation was not observed in any of the treatments except for the application of fluridone, which indicates that de novo ABA synthesis occurs in dormant S. verticillatus seeds during incubation. Besides the physical factors of the environment are related to the control of dormancy, they also regulate the germination of seeds in their natural environment. The sites inhabited by the Eriocaulaceae species are subject to temperature fluctuations and exposed to high luminosity, and these characteristics reflect the germinative patterns of these species. The objective of the second chapter was to evaluate the light and temperature requirements for the germination of five species (Actinocephalus geniculatus, Comanthera bisulcata, Syngonanthus anthemiflorus, Syngonanthus multipes and Syngonanthus niger). Germination tests were carried out at constant temperatures of 15 to 35°C, and the base temperatures (Tb) were calculated for three species. In addition, single (24, 48, 72 and 96 hours) and intermittent (1, 2, 4, 6 and 8 hours for five consecutive days) pulses of white light were applied. Our results showed that all species require long periods of light to germinate. A. geniculatus, S. anthemiflorus and C. bisulcata showed the highest thermal amplitude (15 to 35°C). For S. multipes, the percentage of germination was greater than 50% between temperatures of 17.5 to 30°C and the most restricted thermal range was found for S. niger (20 to 30°C). For the three species selected, the values found for the Tb were compatible with the temperature variations that occur in the campos rupestres.