Streptomyces spp. alleviates drought stress and reduces yield losses by enhancing root development, net photosynthesis, and water-use efficiency in soybean plants.

Abstract

Drought is a major environmental constraint that directly impacts crop productivity and, consequently, decreases seed quantity, quality, and consequently food supply. Bio-inoculants, particularly plant growth-promoting Streptomyces (PGPS), have long demonstrated great potential to contribute to agricultural sustainability. Therefore, it is key to identify new strains capable of mitigating the negative effects of both abiotic and biotic stresses. The objective of this work was to assess the capacity of Streptomyces sp. N2A and S. lydicus N9, previously isolated from soybean [Glycine max (L.) Merr.] rhizosphere and characterized as biostimulants and biocontrol agents, to alleviate the effects of drought stress (DS), experimentally imposed as a moderate soil water deficit at two critical developmental stages. Our results demonstrated that soybean-seed treatment with Streptomyces sp. N2A or S. lydicus N9 at sowing mitigated yield losses under a moderate DS scenario by activating several integrated avoidance strategies and multi-tolerance mechanisms. Improvements in root architecture and optimal stomatal regulation were observed, leading to enhanced water use efficiency. Furthermore, physiological responses such as osmotic adjustment, detoxification of reactive oxygen species (ROS), and maintenance of sodium homeostasis were promoted, resulting in minimized cellular damage, improved photosynthetic performance, and greater carbon assimilation under water-limited conditions. Together, these coordinated morphophysiological and biochemical adjustments enhanced soybean resilience under moderate soil water deficit, highlighting the potential of Streptomyces-based seed treatment as an effective and sustainable strategy to improve crop performance under water-limited conditions.