Endophytic Bacillus inaquosorum and Bacillus safensis Enhanced Growth, Proline Content and Antioxidant Enzymes in Avena sativa L. Under Salt Stress.

Abstract

The study aimed at selecting salt-tolerant endophytic bacteria with the ability to improve growth, proline content, and antioxidant enzymes in Avena sativa (Oat) under salinity. Of 43 endophytic bacteria isolated from various Oat tissues on nutrient agar with 2.5% NaCl, all produced ammonia and auxins. Additionally, 30.2% solubilized phosphate, 83.7% solubilized ZnO, 4.6% solubilized Zn₃(PO₄), 7.0% solubilized ZnCO₃, 69.8% produced siderophores, and 2.3% produced HCN. These isolates also differed in their ability to exhibit growth at different NaCl levels (5-15%). Dendrogram that was generated based on plant growth-promoting traits and salinity tolerance exhibited three clusters and four independent branches. Out of thirteen bacterial isolates selected based on plant growth-promoting traits and salinity tolerance, five isolates showed significantly higher radicle and plumule length of Oat over control on water agar plates. Two promising isolates evaluated for growth promotion, antioxidant, and osmoprotectant activities in two salt-resistant (OL-14, OL-1876-2) and two susceptible (UPO-212, OL-1971) Oat genotypes under salinity in pots significantly enhanced plant height, dry weight, proline content, superoxide dismutase, peroxidase, and catalase activities over the uninoculated control. The SEM analysis showed the colonization of plant tissues by these bacterial strains validating their endophytic nature. Isolates were characterized based on polyphasic approach exhibiting maximum similarity to Bacillus inaquosorum O₃SE₂ and Bacillus safensis O₄SE_1. Salinity-tolerant plant growth-promoting B. inaquosorum and B. safensis as endophytes associated with Avena sativa L. are reported for the first time.