Phyllosphere Diazotrophs of Brinjal: Isolation, Characterization and Assessment of Nitrogen-Fixing Efficiency

Abstract

The rising need for sustainable agricultural practices in modern vegetable production necessitates the exploration of alternative nitrogen sources like plant associated nitrogen fixing bacteria. This study aimed to isolate, characterize and evaluate native foliar bacteria specifically Azotobacter and Azospirillum strains isolated from brinjal (Solanum melongena L.) leaves across various farming environments in the Raipur and Durg districts of Chhattisgarh. A total of 22 native diazotrophic isolates (10 Azotobacter and 12 Azospirillum) were recovered. The Azospirillum exhibited a complete recovery rate even from crop exposed to intensive chemical pesticides, Azotobacter populations were completely missing from these highly stressed areas. This clear difference shows that bacteria with the ability to live inside the plant are far more resilient to harsh conditions than those living entirely on the surface. Our biochemical tests confirmed that these isolates possess essential traits for survival and plant growth promotion, including consistent catalase and urease activity, and an absence of phytotoxic hydrogen sulfide (H₂S) generation. Quantitative in-vitro assays revealed significant variations in nitrogen-fixing capabilities among the isolates. The most efficient Azotobacter strain Bnj Azot 8 fixed 15.28 mg N per gram of sucrose, while the top Azospirillum strain Bnj Azos 5 exhibited an even higher efficiency of 18.52 mg N per gram of malate. The distinct metabolic adaptability and high nitrogen-fixing potential of these locally acclimatized strains present them as highly viable biological agents for the development of foliar bio-inoculants. This method avoids common soil problems and provides a reliable alternative to chemical nitrogen fertilizers for modern vegetable farming.