Molecular Characterization and Plant-Growth-Promoting Activities of Salt-Tolerant Silicate-Solubilizing Bacteria From Sugarcane Rhizosphere; Effect on Watermelon (Citrullus Lanatus) Yield And Nutrient Uptake

Soil salinity limits crop output on 20% of irrigated land worldwide. Silicon-solubilizing rhizobacteria release plant-available silicon and promote plant growth, thus reducing salt stress in an eco-friendly way. This study examined 32 rhizosphere soil samples from sugarcane fields in Baramati (Pune District, India) for pH (7.0–8.5) and salinity (EC 0.5–4.0 dS/m). On nutritional agar with up to 8% NaCl, 128 halotolerant silicate-solubilizing bacterial (SSB) isolates were isolated. 12 isolates thrived well at 8% NaCl, indicating strong salt tolerance, but 12% NaCl reduced growth. Characterizing eight powerful SSB isolates was done. Bacillus tequilensis, Pseudomonas fluorescens, Rhizobium leguminosarum, and Pseudomonas aeruginosa were identified by 16S rRNA gene sequencing. The eight had calcium carbonate (silicate) solubilization, cellulase and protease activity, and indole-3-acetic acid (IAA) synthesis, but no amylase, siderophore, or phosphate-solubilizing activity. Watermelon (Citrullus lanatus) pot tests showed that salt-tolerant SSB isolate inoculation increased plant growth, yield, and nutrient uptake in salty soil. Inoculated watermelon plants had 15–25% higher fruit output and tissue nitrogen, phosphorus, and potassium than uninoculated controls. These results show that halotolerant SSB may mobilize silicon and provide multiple PGP benefits as bio-inoculants for salt-affected soils to boost crop productivity. Silica-solubilizing bacteria; halotolerance; plant growth enhancement; watermelon; salt stress; biofertilizer