Development of a granular bioformulation of Achromobacter xylosoxidans AX77 16S for sustainable onion white rot management and growth enhancement

Abstract

Abstract Onion white rot, caused by Stromatinia cepivora, is a major soil-borne fungal disease that severely affects onion production. This study introduces a novel endophytic bacterium, Achromobacter xylosoxidans AX77 16S, isolated from healthy onion seeds, as a potential biocontrol agent and growth promoter. Out of 78 bacterial isolates screened, AX77 16S showed the strongest antifungal activity, inhibiting pathogen growth by 50% in dual culture assays. Its application significantly enhanced seed germination (up to 82%) and improved shoot and root development, increasing vigor indices by over 100% compared to untreated controls. The strain was identified by biochemical and molecular techniques and registered in GenBank (ON679518). GC–MS analysis revealed ten bioactive compounds in the bacterial filtrate, while scanning electron microscopy confirmed its damaging effects on fungal structures. Additionally, AX77 16S was formulated into a granular product that remained viable for up to one year. This study presents a promising, sustainable, and cost-effective alternative to chemical fungicides for managing onion white rot and promoting crop growth.