Abstract

The chitosan-based bioactivator FF-BR (Patent Nº: US 9,868,677 B2) represents a cutting-edge solution within green chemistry, designed to enhance plant stresses tolerance. Upon application, FF-BR forms a protective film on the plant surface, triggering defense mechanisms. This study evaluated FF-BR’s capacity to mitigate the effects of water deficit in soybean plants under both greenhouse and field conditions, focusing on its impact on grain yield and physiological performance. Our results demonstrate that FF-BR significantly improved intrinsic water use efficiency (iWUE) in both greenhouse (66.70%) and field environments (35%). The net photosynthetic rate increased (8.12%-greenhouse; 12%-field), while stomatal conductance (20.21%-greenhouse; 15%-field) and leaf transpiration (14.30%-greenhouse; 10%-field) were reduced, reflecting enhanced water use efficiency. Additionally, under greenhouse conditions, FF-BR optimized energy dissipation via non-photochemical quenching (NPQ), potentially improving carbon assimilation during sun-shade transitions in crop canopies. Field experiments indicated cultivar-specific responses to FF-BR application. Early-cycle cultivar BMX 51X51 I2X-Trovão exhibited yield increases of 651 kg ha^-1, 515 kg ha^-1, and 667 kg ha^-1 at concentrations of 0.75%, 1.0%, and 1.25% (v.v), respectively. By contrast, mid-cycle Soytech ST 641-I2X showed lower yield improvements of 278 kg ha^-1, 216 kg ha^-1, and 187 kg ha^-1 at the same concentrations, compared to untreated controls. FF-BR also modulated root architecture by reducing growth rates in total root length (16.09%), root volume (41.11%), and surface area (26.04%) under well-watered conditions, while stabilizing root volume growth under drought, suggesting optimized water acquisition and minimized metabolic costs. This suggests that FF-BR enhances root water acquisition efficiency, while minimizing the metabolic costs of root plasticity—an essential adaptation in fluctuating environments. FF-BR offers a sustainable, innovative tool for improving soybean performance under water deficit conditions, enhancing water use efficiency and photosynthetic optimization while reducing ecological impacts. This bioactivator has promising applications for climate-resilient agriculture and long-term crop productivity.

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