Chitosan nanoparticle encapsulation of celery seed essential oil: Antifungal activity and defense mechanisms against cucumber powdery mildew

The objective of the current study was to explore the antifungal potential of celery seed essential oil (CSEO) in a nano-carrier system against Podosphaera fusca, the causal agent of cucumber powdery mildew. We assessed the physicochemical characterization of CSEO-loaded chitosan nanoparticles (CSEO-LCNPs) using dynamic light scattering, field emission scanning electron microscopy, and Fourier transform infrared spectroscopy. The successful loading of various concentrations of CSEO into chitosan nanoparticles (1:0, 1:0.25, 1:0.5, 1:0.75, and 1:1) has been verified. The particles exhibited a spherical shape, with an average diameter of 113 nm, and a negatively charged surface with a zeta potential of -31.5 mV. The Korsmeyer-Peppas model well described the release behavior of CSEO from nanoparticles. Additionally, we examined the defense mechanism, as well as biochemical/molecular responses following foliar treatment with CSEO-LCNPs. In vivo, results revealed that CSEO-LCNPs foliar application on the cucumber seedlings inoculated with P. fusca significantly reduced the disease severity of powdery mildew. Treatment with CSEO-LCNPs led to an increase in phenolic and flavonoid compounds, chlorophyll concentration, enzyme activities, and gene transcriptions in inoculated cucumber seedlings. In our study, we observed a positive correlation between antioxidant compounds and the defense-associated enzymes as well as their corresponding gene expressions. Our study underscores the potential of CSEO-LCNPs as an eco-friendly and effective solution for managing cucumber powdery mildew.