Dual potential of Bacillus pumilus PAD5 isolated from Eryngium foetidum: biocontrol of Sclerotium rolfsii and growth promotion in rice.

The endophytic isolate PAD5, derived from Eryngium foetidum L. and identified as Bacillus pumilus strain PAD5 (KX350056), demonstrated remarkable characteristics including phosphate solubilization (7.5 µg/ml), indole-3-acetic acid (IAA) production (31.13 µg/ml), biofilm formation, siderophore, hydrogen cyanide (HCN), and exo-polysaccharide production. It exhibited robust growth on nitrogen-free media, high salt conditions (6%), and low pH (5.0). The isolate showed potent antagonistic activity against Sclerotium rolfsii. Gas chromatography-mass spectrometry (GC-MS) analysis of the crude extract revealed the presence of five major and 19 minor active compounds. When applied in conjunction with the pathogen (SrBp), the PAD5 isolate remarkably enhanced rice growth after 20 days of transplanting, recording substantial increases over the pathogen (Sr) treatment shoot length by 175.8%, shoot fresh weight by 193.5%, shoot dry weight by 161.0%, root length by 106.5%, root fresh weight by 114.3%, and root dry weight by 129.2%. These pronounced improvements indicating PAD5's strong potential in promoting plant growth even under pathogen-induced stress. Additionally, the PAD5 isolate induced systemic response and enhanced host defense physiological activities, as evidenced by elevated plant defense enzyme such as Phenylalanine ammonia lyase (PAL), Total phenol content (TPC), Polyphenol oxidase (PPO), and Superoxide dismutase (SOD) enzyme activities in seedlings treated with either isolate PAD5 alone or in combination with the pathogen (SrBp).