Enhanced seedling growth of annual medic under salt-drought stress through ultrasonic wave and magnetic field treatments

Annual medic (Medicago scutellata L.) is a crucial legume that exhibits significantly reduced growth rates during germination under salt and drought stress conditions. This study aims to identify the sensitive components of seedling growth in response to these stresses. In the first experiment, seeds were exposed to magnetic fields of 125 and 250 mT for varying durations (1, 2, 4, and 6 h). In the second experiment, seeds were subjected to ultrasonic waves for different durations (2, 4, 6, 8, and 10 min). Both experiments involved various osmotic pressures (OP) induced by NaCl (0, − 2, − 4, − 6, and − 8 MPa) and PEG 4000 (matching OPs) with three replications each. The results indicated that seedling growth rate (SGR), weight of mobilized seed reserve (WMSR), seed reserve depletion (SRDP), and seed reserve utilization efficiency (SRUE) were significantly impacted by salt and drought stresses. The highest seedling dry weight (SLDW) of 0.39 mg was observed in the magnetic field treatment at 250 mT for 4 h, while the highest SRUE of 0.96 mg seed−1 was achieved with ultrasonic wave treatments of 4 min under − 2 MPa drought stress. Under drought stress (− 2 MPa), the maximum root length (24.2 mm), shoot length (12.4 mm), seed germination (87.09%), WMSR (0.41 mg seed−1), and SRDP (96.32%) were obtained with a 4-min ultrasonic treatment. Additionally, the highest SLDW (0.41 mg) and SRUE (0.97 mg seed−1) were observed in the magnetic field treatment at 250 mT. Pre-sowing treatments with magnetic fields (250 mT for 4 h) and ultrasonic waves (4 min) can effectively enhance salt and drought tolerance in dry seeds of annual medic.