Exploration and Characterization of Native Rhizobacteria from Saline Soils of Brebes, Indonesia for Growth Promotion of Allium ascalonicum L.

Abstract

Aims: The present study was design to investigated the potential of rhizosphere bacteria as plant growth-promoting rhizobacteria (PGPR) to enhance shallot growth in salinity-affected soils. The focus objectives were to identify and characterized bacterial isolates capable of producing indole-3-acetic acid (IAA), solubilizing phosphate, and tolerating high salinity levels. Study Design: The experiment was carried out in a survey method combined with purposive sampling. Place and Duration of Study: Soil samples were collected from a coastal agricultural area in Brebes Regency, Central Java, Indonesia. Laboratory analyses were conducted between August and December 2024 at the Microbiology Laboratory and the Integrated Research Laboratory, Faculty of Biology, Jenderal Soedirman University, and Laboratory of the Agricultural Instrument Standardization Center, Bogor, Indonesia. Methodology: Rhizosphere soil samples were collected from the root zone using purposive sampling and cultured on selective media. The selected isolates were then subjected to salinity tolerance testing, phosphate solubilization, indole-3-acetic acid (IAA) production, siderophore production, and nitrogen fixation assays. Results: The highest indole-3-acetic acid (IAA) production was recorded in isolate KL1K2, while the greatest phosphate solubilization activity was exhibited by isolate KL3ASH1. Nitrogen fixation ability was observed in isolates KL1K2, KL4ASH3, K4K1, K4P1, K4RZ3, K4RZ6, K3RZ1, K3IS4, and KL3ASH1. Additionally, siderophore production was detected in isolates KL1K2, K3RZ1, K4RZ3, K4P1, and KL4ASH3. Conclusion: Among all tested isolates, KL3ASH1 and K3IS4 met all selection criteria and exhibited stable nitrogenase activity. These strains are promising candidates for bio-inoculant development, particularly for improving crop productivity in saline soil environments.