Bioprospecting osmotolerant phyllosphere bacteria: functional characterization and biotechnological application for enhanced nutrient use efficiency in solanum crops.

This study investigated a targeted foliar inoculation strategy using phyllosphere-competent epiphytic bacteria to enhance the agronomic performance of solanaceous crops, specifically tomato and brinjal, while circumventing barriers to rhizosphere establishment. Bacterial isolates from the phyllosphere of tomato and brinjal leaves, collected from two distinct agro-climatic regions, were screened for osmotolerance, nutrient mobilization, nitrogen fixation, and biocontrol traits. This was followed by molecular identification and the assessment of selected strains as foliar inoculants under conditions of 75% of the recommended fertilizer dose. Through this screening, 14 resilient isolates were identified, predominantly from the genera Acinetobacter and Bacillus. Multivariate and correlation analyses established a strong statistical association between stress-induced accumulation of intracellular proline and extracellular polysaccharides (EPS) and key agronomic outcomes, including enhanced in vivo root biomass and nitrogen (N) uptake. During in vivo pot trials, temporally precise foliar sprays were administered 5 days post-transplantation and 45 days post-germination to mitigate transplant shock and support reproductive transitions. To rigorously evaluate the fertilizer-saving potential, bacterial treatments were assessed under a reduced synthetic input regime (75% of the Recommended Dose of Fertilizer, RDF). The top-performing isolates, Bacillus stercoris KBL91 and Bacillus subtilis VBR72, when applied in combination with 75% RDF, consistently outperformed the uninoculated 100% RDF standard baseline. Specifically, B. stercoris KBL91 doubled tomato root biomass and achieved exceptional Nutrient Use Efficiency (NUE) scores exceeding 100% for all macronutrients, peaking at 159.43% for potassium. Concurrently, B. subtilis VBR72 demonstrated robust biocontrol efficacy by inhibiting the late blight pathogen, Phytophthora infestans, by 87.44%. In conclusion, the targeted foliar application of indigenous osmotolerant epiphytes offers a highly effective and ecologically sustainable approach to significantly reduce synthetic fertilizer dependency (by at least 25%) while enhancing crop resilience, vegetative growth, and pathogen defense.