Ciclos de Hidratação e Desidratação na germinação de sementes de Cosmos sulphureus sob estresse hídrico

Abstract

Cosmos sulphureus is a ruderal species, able to develop in different places, such as along sidewalks, manholes, asphalt cracks and vacant lots. Due to the development of this species in such an inhospitable environment, studying its seed physiology is essential for understanding the herbaceous species that occur in urban areas. This work aimed to evaluate the performance of C. sulphureus seeds after being submitted to hydration and dehydration cycles and to evaluate if they have water memory. With this proposal, germination tests were carried out at different temperatures: 20-30; 25; 30; 35; and 40°C to determine the ideal temperature. Then, the seeds were submitted to 1, 2 and 3 cycles of hydration and dehydration for different periods (0.5, 6 and 12 hours) and evaluated in germination tests with substrate moistened with water or with a PEG 6000 solution at different water potentials (Ѱꙍ): 0 (distilled water), -0.1 MPa; -0.2 MPa; -0.5 MPa; -0.7 Mpa, and also the control (no cycle). As result, it was possible to observe that the seeds of C. sulphureus presented germination percentages in the different temperatures varying between (63 and 89%), and the ideal temperature was 30°C. After the seeds were subjected to hydration and dehydration cycles, the percentages of seed germination in the potentials were: 0 Mpa (between 84 and 97%), -0.1 Mpa (between 79 and 95%), and -0.2 Mpa (between 69 and 92%). However, with the increase in the PEG 6000 concentration, there was a decrease in the germination percentage, which was less than 20% at -0.7 Mpa. Given the above, C.sulphureusseeds have a wide temperature range to germinate, and after being subjected to hydration and dehydration cycles, they improved their performance compared with the control. In the most negative osmotic potentials (-0.5 and - 0.7 MPa) it was possible to identify the water memory of C. sulphureus seeds.