Ultrasonic waves improve aged seed germination of castor bean (Ricinus communis L.) under drought and salt stresses.

Castor bean (Ricinus communis L.) is an important oilseed crop which can be applied for medicinal and industrial uses. Since there is no study concerning the aged castor bean seed germination response induced by ultrasound treatment under water and salt stresses. This study aimed to model the germination response of this plant under all applied treatments (i.e., aging, water deficit, salt stress, and ultrasound treatments) using mathematical models. Castor bean seeds were initially aged at 41 °C at different periods (0, 2, 4, 6, 8, and 10 days) to provide a range of sub-lots with various seed vigor. At each sub-lot, the seeds were randomly divided into two subsamples, one for ultrasound and the other for non-ultrasound treatment at each of the following water potentials (ψ; 0, − 0.4, − 0.8 and − 1.2 MPa; made by both polyethylene glycol 8000 and sodium chloride). At all treatments, the germination parameters were recorded. Electrolyte leakage of the seeds was measured and osmotic adjustment into the castor bean seeds was also estimated. The germination percentage and germination rate of castor bean seeds were significantly influenced by all the above-mentioned treatments (P < 0.01). At each aging period, the hydrotime model could accurately quantify the castor bean germination response under various ψs (made by PEG and NaCl) with R² value of > 0.80. The aged and non-aged castor bean seeds could uptake the salt ions, adjust their potential and then improve their germination under saline conditions. Under non-ultrasound treatment, the osmotic adjustment was higher compared to ultrasound treatment because ultrasound can cause cell membrane damage, increase permeability by fissures on the pericarp and so reduce the ability of cells for adjusting turgor pressure into seeds. The conductivity significantly increased with aging, reflecting seed vigor loss. Ultrasound treatment increased germination parameters in both aged and non-aged seeds across all ψs, suggesting this treatment could be used as pretreatment in castor bean seeds for improving germination characteristics, particularly under stressful conditions. Consequently, the parameters reported in the present work can be successfully used in castor bean germination simulation models. However, some field experiments will be required to examine the ability of this technique in natural conditions, which can be a suitable avenue for further research. [ABSTRACT FROM AUTHOR]