Pseudomonas fluorescens NK4 siderophore promotes plant growth and biocontrol in cucumber

Aims To test the effect of zinc oxide nanoparticle (ZnO-NP) supplementation for enhancing the efficacy of Pseudomonas fluorescens NK4 siderophore as a biocontrol agent against P. viridiflava NK2 and a plant growth promoter. Methods and Results Cucumber seedlings were treated with a suspension of P. fluorescens NK4 and its siderophore generated in siderophore-inducing medium (SIM), SIM supplemented with ZnO-NP (<100 nm) and SIM supplemented with Zn2+ ions from Zn(NO3)(2). Supplementing SIM with ZnO-NP increased siderophore secretion in P. fluorescens NK4, and irrigation of cucumber seedlings with a filtrate containing the ZnO-NP-supplemented siderophore increased survival, improved vegetative and root growth, and thus increased yield similar to the effects of dipping seedlings in a P. fluorescens NK4 suspension. Both P. fluorescens NK4 and its ZnO-NP-supplemented siderophore inhibited P. viridiflava NK2 population growth in planta. Conclusions The siderophore of P. fluorescens NK4 produced by ZnO-NP supplementation can be employed as a biocontrol agent and biofertilizer. Significance and Impact of the Study ZnO-NPs can boost the synthesis of siderophores, which can then be employed as biofertilizers to boost iron bioavailability in iron-deficient soils.