Seed biopriming with Parachlorella, Bacillus subtilis, and Trichoderma harzianum alleviates the effects of salinity in soybean

Background Seed conditioning with bioinputs (biopriming) offers a promising and sustainable alternative to mitigate the adverse effects of salt stress on soybeans. This study aims to evaluate the potential of isolated or combined biopriming using microalgae and different microorganisms in alleviating salinity-induced stress in soybeans. Methods Seeds were subjected to five biopriming treatments: microalgae Parachlorella sp., Bacillus subtilis , Trichoderma harzianum , Parachlorella sp. + B . subtilis , and Parachlorella sp. + T . harzianum , along with a control group without biopriming. Subsequently, the seeds were exposed to two conditions: i) control (0.0 MPa), and ii) salinity induced by NaCl (-0.8 MPa). Germination, photochemical indicators, and seedling performance were assessed. Results Salinity impaired root protrusion and seed physiology, resulting in a high percentage of abnormal seedlings, thus creating a stressful condition. However, biopriming alleviated the negative effects of salinity, particularly with T . harzianum , Parachlorella sp. + B . subtilis , and Parachlorella sp. + T . harzianum , which led to high germination rates and normal seedlings. All biopriming treatments, especially the combined ones, reduced the suppression of non-photochemical quenching, thereby enhancing the maximum yield of photosystem II. Seedlings under salt stress without biopriming exhibited short lengths and low fresh and dry mass, whereas those bioprimed with Parachlorella sp. + B. subtilis and Parachlorella sp. + T . harzianum showed significantly higher values. Conclusion Seed biopriming, especially with Parachlorella sp. combined with B. subtilis or T . harzianum , effectively alleviates the stressful effects of salinity on soybeans.