Germinação de sementes de pau-ferro submetidas a diferentes condições de armazenamento, escarificação química, temperatura e luz

Abstract

Caesalpinia leiostachya (Benth.) Ducke (Caesalpinaceae) is a tree species native to Brazil, whose seed dormancy is imposed by a waterproof coat. In this study two experiments using different periods of seed immersion in concentrated sulphuric acid in order to break dormancy were carried out. In the first experiment, seeds collected in August 1997 were stored for eight months either at room temperature inside the fruits or under dry chamber conditions after their extraction from the fruits. After storage, the seeds were immersed in sulphuric acid for 0, 10, 20, 40, 60, and 80 min and germination tests were conducted at constant (25°C) and alternating (20°-30°C) temperatures, under an eight hour photoperiod. The second experiment was carried out with seeds extracted from fruits collected in August 1998 and immediately immersed in sulphuric acid for 0, 10, 20, 30, 40, 50, and 60min. Germination tests were conducted at 25°C and 20-30°C, in darkness and under white light. Both germination total percentage and speed of germination index were evaluated. The results showed that (a) the storage of seeds inside of fruits during the considered period is a viable alternative; (b) fresh seeds are indifferent to light at the two tested temperatures; (c) germination speed index either of fresh or of stored seeds is higher at 25°C; (d) seed storage brought about a reduction in dormancy level so that exposing them to sulphuric acid for 10 minutes was enough to overcome seed dormancy; (e) in recently harvested seeds, the period of time of exposition to sulphuric acid needed to break dormancy was found to be between 20 and 30 minutes.