Estratégias para a mitigação dos efeitos do déficit hídrico e salinidade na germinação de sementes e desempenho de plântulas de soja

Abstract

Soybean is one of the world's major agricultural crops and plays a strategic role in the Brazilian economy. However, abiotic factors such as salinity and water deficit impair seed germination and early seedling establishment, reducing crop productivity and stand uniformity. In this context, investigating sustainable alternatives to mitigate these adverse effects is essential. This study was based on the hypotheses that (i) salinity and water deficit negatively affect soybean seed germination and early seedling growth, and (ii) inoculation with Biozyme®, the seaweed extract Kappaphycus alvarezii, and Trichoderma harzianum alleviates stress effects, promoting seedling growth and vigor. Two independent experiments were conducted using seeds of the soybean cultivar 64HO114 IPRO inoculated with: (a) Biozyme® and (b) Trichoderma harzianum, Kappaphycus alvarezii, and K. alvarezii + T. harzianum. In both experiments, seeds were subjected to three experimental conditions: control (no stress), salinity induced by NaCl, and water deficit induced by PEG 6000, both at an osmotic potential of −0.2 MPa. Overall, the studied cultivar proved to be sensitive and responsive to both stress factors, particularly water deficit, which drastically reduced germination parameters and seedling performance compared with the control treatment. In the first experiment, Biozyme® enhanced radicle protrusion, germination, and early seedling growth under both stress conditions, resulting in a higher proportion of normal seedlings and improved root development. Under salinity, it was particularly effective in maintaining shoot biomass accumulation, while under water deficit it preserved membrane integrity. In the second experiment, T. harzianum applied alone was the most consistent treatment, maintaining the highest germination rates under water deficit and promoting the greatest seedling length and biomass accumulation under control conditions. In contrast, K. alvarezii applied alone showed superior performance under salinity by enhancing shoot growth, whereas the combined application of K. alvarezii and T. harzianum produced more variable responses and was not consistently superior to the control. Biozyme® was the most consistent treatment, mitigating the adverse effects of both salinity and water deficit on germination, seedling vigor, and membrane integrity in soybean seedlings. Trichoderma harzianum promoted growth and biomass accumulation under non-stress conditions and maintained germination under water deficit, whereas the K. alvarezii extract was particularly effective under salinity by stimulating shoot growth and protecting root membrane integrity, although, when applied alone, it intensified the effects of water deficit. Therefore, the choice of bioproduct should consider the predominant stress condition: Biozyme® and T. harzianum are recommended under water deficit, whereas K. alvarezii is more suitable under salinity.