Enhancement of phosphate solubilization by endophytic bacteria under salinity and phosphorus deficiency stress conditions

Abstract

Soil salinization and phosphorus (P) deficiency are critical environmental challenges that severely limit global ag - ricultural productivity, particularly in the arid regions of Uzbekistan. Under saline conditions, P is rapidly immobilized, becoming unavailable for plant uptake, which leads to stunted growth and significant yield losses. This study addresses the urgent need for sustainable bio-remediation by evaluating halotolerant endophytic bacteria as effec - tive bio-fertilizers. Several endophytic bacterial strains isolated from native halophytes were screened for their tolerance to extreme salinity (up to 10% NaCl) and their ability to solubilize insoluble phosphates. The most potent isolates, Pseudomonas putida KoPr129 and Bacillus amyloliquefaciens HAPH2, were biochemically characterized for plant growth-promoting (PGP) traits, including IAA, ammonia, and HCN production. A 6-week greenhouse pot experiment was conducted to validate their efficacy on wheat ( Triticum aestivum L.) under 150 mM NaCl stress and P-deficient conditions. In vitro assays confirmed that P. putida KoPr129 maintained a robust phosphate solu - bilization index (FPI 18.16±0.56 mm) even at 10% NaCl. Greenhouse trials demonstrated that inoculation with these endophytes significantly mitigated the negative impacts of combined stress. Specifically, P. putida KoPr129 increased wheat shoot length by 9% and more than doubled the total phosphorus uptake (over 130% increase) compared to the non-inoculated stressed control. Biochemical profiling revealed high levels of IAA produc - tion in both strains, facilitating enhanced root architecture and nutrient acquisition. Our findings demonstrate that halotolerant endophytes, particularly P. putida KoPr129, are superior candidates for the development of effective bio-inoculants. These results provide a promising pathway to restore soil fertility and improve wheat productivity in degraded, saline-alkali landscapes, offering a sustainable alternative to chemical fertilizers.