First report of a Citrobacter sp. for fungal plant disease control: phenethyl alcohol‐producing NJC30 suppresses target spot on soybean

BACKGROUND Target spot, caused by the fungal pathogen Corynespora cassiicola , is a worldwide devastating disease that can affect multiple soybean tissues, including leaves, petioles, stems, pods, roots, and seeds. The control of target spot has traditionally relied on the application of synthetic fungicides, such as carbendazim. RESULTS In this study, Citrobacter si. NJC30 (Enterobacteriaceae family), which was isolated as an endophyte from healthy common comfrey leaves ( Symphytum officinale ) and identified by 16S rRNA , gyrB , and rpoB gene sequencing, was screened as a biocontrol agent to control target spot. NJC30 inhibited C . cassiicola mycelial growth in vitro and exhibited multiple antifungal mechanisms, such as competition for space and nutrients, and the production of phenethyl alcohol, which was present at 66.2 ± 8.6 mg L −1 concentration after 3 days of culture. Preventive application of 1 × 10 9 NJC30 cells/mL reduced target spot symptoms by 83.9% on pods and 74.2% on leaves, showing higher efficacy than 0.25 mg mL −1 carbendazim. CONCLUSION Collectively, a new efficient biocontrol method for the management of target spot has been developed in this study. Although Citrobacter strains have been previously used to promote plant growth and enhance plant tolerance to abiotic stresses, this is the first report on the use of Citrobacter for the management of fungal plant pathogens, revealing a novel and promising biocontrol function for this genus and expanding the toolkit for sustainable plant disease management.