Potencial fisiológico de sementes de Tephrosia noctiflora Bojer ex Baker em função de fatores abióticos

Abstract

Understanding the behavior of the physiological potential of the seeds of different species is crucial for developing strategies to reduce the seed bank. Tephrosia noctiflora, found in various crops and pastures, is toxic and causes dermatopathy in cattle, generating economic losses. However, there is a lack of scientific studies on its fruits and seeds, making it difficult to control them properly. The physiological potential was assessed at five temperatures (20, 25, 30, 35 and 20-30oC), in the presence and absence of light, in a completely randomized design, with a 5x2 factorial scheme (temperature x light) and four replicates of 25 seeds each. The variables studied were: germination percentage, speed index, average time, average speed and relative frequency. Next, using the best temperature of 30 oC, the physiological potential of intact seeds and seeds scarified in sulphuric acid for 25 minutes were assessed as a function of pre-treatment with high temperatures (80, 120, 160, 200, 240 oC) for 5 minutes in a DIC and 5x2 factorial scheme (temperature x scarification); different concentrations of aluminum (0.0; 1.5; 3.0; 4.5 and 6.0 mmolc. dm-3 of Al3+); calcium (0.0; 1.5; 3.0; 4.5 and 6.0 cmolc.dm-3 of Ca3+); and water stress with PEG 6000 at different osmotic potentials (0.0; -0.3; -0.6; -0.9; -1.2 and -1.5 MPa). The experiments were carried out in a completely randomized design (DIC) and the data was submitted to analysis of variance, with means evaluated using the Tukey test at 5% and regression analysis for the quantitative variables. The variables studied were: percentage, speed index, average time, average speed, germination synchrony, length of aerial part and root, fresh and dry mass of root and aerial part for water stress with PEG 6000. The results showed that the best germination occurred at constant temperatures of 20 oC and 30 oC, and at alternating temperatures of 20-30 oC, both in the presence and absence of light. Pre-treatment with high temperatures revealed that the species is not very susceptible to exposure to high temperatures, not germinating above 120 oC. Germinability was significantly affected from 1.5 mmolc.dm-3 of Al3+, and calcium levels indicated sensitivity from the initial dose of 1.5 cmolc.dm-3. Water stress caused a decrease in germination as osmotic pressures increased.

Key words: weed, aluminum stress, water stress, integrated management.