Evaluation of Bio-Friendly Formulations from Siderophore-Producing Fluorescent <i>Pseudomonas</i> as Biocontrol Agents for the Management of Soil-Borne Fungi, <i>Fusarium oxysporum</i> and <i>Rhizoctonia solani</i>

Abstract

Secretion of siderophores by Pseudomonas aeruginosa F2 and P. fluorescens JY3 was evaluated on chrome azurol S (CAS) agar plates and their inhibitory effect was inspected against Fusarium oxysporum and Rhizoctonia solani. Production of siderophores as biocontrol agents from F2 and JY3 was accomplished in two optimized media. Afterward, cell-free supernatants of the bacterial cultures containing siderophores were used for the preparation of two bio-friendly formulations for the management of F. oxysporum and R. solani under greenhouse conditions. The investigated bacterial isolates, F2 and JY3, showed antagonistic activity in vitro against F. oxysporum and R. solani and produced siderophores in optimized media with high efficiency. Colonies of both bacterial isolates were grown exponentially with a constant specific growth rate of 0.07 h−1 and 0.27 h−1, correspondingly. Siderophores estimated in 10 µL reached their highest value of 16.95% at 47 h and 19.5% at 48 h for isolate F2 and JY3, respectively. Formulations of siderophore-generating F2 and JY3 reduced damping-off caused by F. oxysporum by 40% and 80%, while the reduction percentage of damping-off caused by R. solani reached 87.5% and 62.5%, correspondingly. Moreover, both formulations encouraged the growing of wheat plants where the fresh and dry weight of shoots and roots were increased compared to the treatment with each fungus. In conclusion, bio-friendly formulations resulting from this investigation can play an active role in managing soil-borne diseases.

Keywords

• siderophores
• biocontrol
• <i>Pseudomonas aeruginosa</i>
• <i>Pseudomonas fluorescens</i>
• bioformulation