Impact of Wheat-Associated Rhizobacteria on Suppressing Common Root Rot in Wheat Caused by Bipolaris sorokiniana

Abstract

This study aimed to isolate plant growth-promoting rhizobacteria (PGPR) from Iranian wheat rhizospheres, identify promising antagonists and evaluate their capacity to antagonize Bipolaris sorokiniana and enhance wheat growth. Rhizosphere soils from wheat plants collected across multiple provinces yielded 640 bacterial isolates, which were screened in vitro using a dual-culture assay on PDA to quantify the inhibition of fungal growth. Seventeen strains showed significant antagonism (60%–~96% inhibition), and five superior strains (BAW2R35, GFW16R5, EW17R5, KBW9R1 and MFW14R3) were characterized by biochemical tests and 16S rRNA sequencing and evaluated in greenhouse assays on two cultivars (Azadi, Sirvan) using seed bacterization, with B. sorokiniana challenge. The selected strains were identified as Bacillus spp. (BAW2R35, GFW16R5, EW17R5), Pseudomonas aeruginosa (KBW9R1), and Pseudomonas chlororaphis (MFW14R3) exhibited multiple PGPR/antagonistic traits, including ammonia and siderophore production (all 17 strains), hydrogen cyanide production (Pseudomonas strains), nitrogen fixation, phosphate solubilization, antifungal metabolite activity and extracellular enzymes. In greenhouse experiments, growth promotion and disease suppression depended on the cultivar and strain: P. chlororaphis achieved the highest control efficacy in Sirvan (47%), whereas Bacillus sp. GFW16R5 was most effective in Azadi (43%). P. chlororaphis also induced the greatest increases in leaf antioxidant defences and soluble proteins, particularly under co-inoculation with the pathogen (SOD, POD, CAT and protein increases up to 13%, 22.19%, 28.43% and 25%, respectively). These findings indicate that native wheat rhizobacteria, particularly P. chlororaphis and selected Bacillus spp., can partially suppress common root rot while enhancing plant growth and host defence, supporting their development as components of environmentally friendly disease management strategies. However, field validation and consortium testing are still required.