Selenium Nanoparticles (SeNPs) Inhibit the Growth and Proliferation of Reproductive Structures in <i>Phytophthora capsici</i> by Altering Cell Membrane Stability

Selenium nanoparticles (SeNPs) are currently receiving attention for controlling plant pathogenic microorganisms, are expected to be especially effective against the genus <i>Phytophthora,</i> and show high anti-oomycete activity. SeNPs synthesized with plant extracts have shown low toxicity, high bioavailability, and mechanisms of action that alter cellular integrity and damage key components of phytopathogen metabolism, causing denaturation and cell death. The aim of this study was to evaluate the inhibitory activity of SeNPs on mycelial growth and the development of reproductive structures in <i>Phytophthora capsici</i> in vitro. Different concentrations of SeNPs (0 to 400 µg/mL) in culture media were used to analyze mycelial growth, sporangium formation, zoospores, and germination of the germ tube. To explain the changes in morphology and development of <i>P. capsici</i>, increased relative conductance and activation of glycerol synthesis were related to osmotic stress and damage to membrane permeability. In addition, SeNPs inhibited the production of exopolysaccharides (EPSs), which are compounds associated with pathogen virulence. A lower accumulation of its biomass evidences alterations in the oomycete growth. The percentage of inhibition of mycelial growth increased with higher SeNP concentrations and incubation time, reaching 100% growth inhibition at 300 and 400 µg/mL. A concentration-dependent reduction in the number of spores, sporangia, and zoospore germination was observed. Concentrations of 50 and 100 µg/mL of SeNPs reduced biomass production by 30%. The increase in glycerol levels indicated an osmoregulatory response to SeNP-induced stress. Also, the increase in electrical conductivity suggested plasma membrane damage, which supports the potential of SeNPs as antifungal agents by inducing cell disruption and structural damage in <i>P. capsici</i>. These results provide new knowledge on the in vitro mechanism of action of SeNPs against <i>P. capsici</i> and offer a new biological alternative for the control of diseases caused by oomycetes.