Multitrait Root Endophytic <i>Bacillus subtilis</i> BREB 03 Reduce <i>Heterodera avenae</i> Infestation in Barley

Cereal cyst nematode (Heterodera avenae) significantly hampers barley production by causing stunted growth and yield losses. This study explored the biocontrol potential of multitrait root endophytic bacteria isolated from H. avenae-infested barley roots to suppress nematode infestation. Ten endophytic bacterial strains were isolated and screened for their inhibitory effects on cyst hatching. Among them, Bacillus subtilis BREB 03 exhibited the highest hatching inhibition (48.31%), outperforming the bio-control check Azotobacter chroococcum HT-54. The promising root endophytic bacterium BREB 03, identified as a Gram-positive rod-shaped bacterium, exhibited optimal growth at 25°C and halotolerance up to 10% NaCl, along with diverse metabolic capabilities including positive catalase, oxidase, citrate utilization, and fermentation of multiple sugars. Whole-genome sequencing and phylogenomic analysis confirmed the identity of BREB 03 as B. subtilis. Further in vitro assays revealed BREB 03 capabilities for siderophore production, ammonia excretion, indole acetic acid (IAA) synthesis, and phosphorus solubilization, contributing to both nematode suppression and plant growth promotion. Seed treatment with BREB 03 significantly enhanced barley growth parameters, indicating its dual role as a biocontrol agent and biofertilizer. This study highlights B. subtilis BREB 03 as a promising alternative for sustainable management of cereal cyst nematode in barley, with potential to reduce reliance on chemical nematicides.