Use of ultrasound to overcome dormancy in <i>Ochroma pyramidale</i> seeds

Abstract

The objective of this work was to evaluate the effect of ultrasound waves, in a continuous mode, at different frequencies, intensities, and exposure times on the pre-germination treatment of seeds of Ochroma pyramidale, a species commonly known as balsa tree. For the germination and emergence tests in sand, a completely randomized design was adopted, with four replicates of 50 seeds each. Ten treatments were evaluated: control (T1); hot water at 80°C (T2); and ultrasound (T3 to T10) adjusted at different combinations of frequencies (1.0 and 3.0 MHz), intensities (1.0 and 2.0 W cm^‑2), and exposure times (2 and 3 min). T2 showed the best percentage of germination (84%), followed by T8 (70%). Regarding the germination speed index, T2 and T8 presented the best values of 7.35 and 6.83, respectively. T2 also showed the best emergence speed index of 4.65. Although immersion in hot water at 80°C stands out as the best method, the ultrasound in T8 (at a frequency of 1.0 MHz, intensity of 2.0 W cm^-2, and exposure time of 3 min) has a positive effect on overcoming dormancy in seeds of the evaluated species.