Assessing the Effectiveness of Granular and Cell Suspension PGPR Biofertilizers in Enhancing Rice Growth in Saline Soils.

Abstract

In agriculture, plant growth-promoting rhizobacteria (PGPR) plays an important role in increasing soil quality and enhancing plant growth. However, the relative efficacy of various PGPR delivery modalities, such as granules and microbial suspensions, is uncertain. The aim of this study was to compare the efficiency of 12 salt-tolerant PGPR isolates as biofertilizers in two different formulations to determine which better supports rice seedling growth and microbial persistence under salinity stress. The selected isolates were tested for essential plant growth-promoting properties such as IAA synthesis, nitrogen fixation, phosphate and potassium solubility, ACC-deaminase activity, siderophore generation, and biofilm formation. Among the isolates, Mesorhizobium sp. S1-7 showed the highest IAA production at 74.43 μg/ml. Microscopic analysis confirmed that Enterobacter aerogenes P8, Shinella sp. R18, and Mesorhizobium sp. S1-7 successfully colonized rice roots under varying salinity levels (0, 2, 4, and 8 dS/m). In a pot experiment, both formulations increased rice seedling development in normal and saline environments. The liquid form exhibited greater stability during storage, whereas the granular form discharged more microbial cells into the soil. Despite their similar impacts on plant growth, the granular form has a significant advantage due to its slow-release qualities, which promote microbial persistence and long-term advantages in tough settings like saline soils. This study highlighted the potential of Enterobacter sp., Shinella sp., and Mesorhizobium sp. in granular biofertilizer formulations and contributed to developing optimized biofertilizer strategies for enhancing crop productivity in salinity-affected regions.