Comportamento germinativo de espécies do gênero Stachytarpheta Vahl. (Verbenaceae) ocorrentes nos campos rupestres da Cadeia do Espinhaço em Minas Gerais

Abstract

The present work studied the seed germination ecology of thirteen Stachytarpheta Vahl species, twenty-two populations and a hybrid between S. glabra Cham. and S. confertifolia Mold., occurring in the Rock Outcrops of the Espinhaço Range in its Minas Gerais state portion, in Brazil. Were evaluated biometrics, light and temperature influences, in addition to the pre-treatment effects of dry storage and gibberellin application (GA3) on seeds germination. These pre-treatments were applied as recently collected seeds normally had shown low germination rates. Intraspecific differences in the germination of four species were also evaluated. The seeds viability was tested through the tetrazolium test. The assays were conducted in germination chamber with 6 constant temperatures (15 to 40°C; with intervals of 5°C) under 12 hours photoperiod and dark, and under the fluctuating temperature of 30/15°C (L/E). The gibberellin assays (GA3) were performed at 30°C with concentrations of 250 and 500 ppm. The results show that the Stachytarpheta species have small seeds; most of them being photoblastic positive, showing higher germination rates at 25 and 30°C and at the fluctuating temperature. However inter and intraspecific differences in germination behavior were found, showing the existence of different germination patterns with differences in dormancy within the genus. These results indicate that the germination ecology has an association with the habitat occupied by the species. Rock outcrops species have seed dormancy, presenting germination rates always lower than their viability, while S. reticulata, typical Cerrado species and S. cayennensis, widespread species did not show dormancy. The pre-treatments results indicate that these break the dormancy for most tested species, increasing significantly the germination percentage of these. The results show that Stachytarpheta seeds dormancy has non-deep physiological dormancy.