Rhizobacteria Act on Photosynthetic and Protective Metabolism of Sugarcane Varieties Subjected to Water Deficit

Abstract Sugarcane cultivation in Brazil is a major agricultural industry, generating employment and playing a vital role in the production of sugar and ethanol. To maintain high productivity, appropriate management and cultural practices are essential, particularly during the sprouting phase, which is vulnerable to water stress. This study aimed to mitigate the effects of water stress during the sugarcane transplanting through the inoculation of plant growth-promoting rhizobacteria (PGPR) at planting. The responses of photosynthetic metabolism and defense mechanisms, as well as plant growth, were evaluated in two sugarcane varieties RB966928 and CTC7515BT exposed to the following conditions: control (70% of soil water retention capacity, WRC), water deficit (WD): 40% WRC, WD + Bacillus subtilis , and WD + Mix ( B. subtilis , B. pumilus , and B. amyloliquefaciens ). Results showed that drought stress significantly reduced developmental potential and biomass accumulation, as well as negatively affected water content and gas exchange parameters, including photosynthesis, transpiration, stomatal conductance, and intercellular CO₂ concentration. However, the inoculation of PGPR enhanced the enzymatic activity of peroxidase and superoxide dismutase in both cultivars, alleviating the negative effect of water deficit. Therefore, PGPR inoculation represents a promising strategy to alleviate water stress, promote antioxidant enzyme activity, and enhance crop resilience, ultimately contributing to sustainable sugarcane production.