Biocontrol Mechanisms of Three Plant Essential Oils Against Phytophthora infestans Causing Potato Late Blight.

Late blight, caused by the notorious pathogen Phytophthora infestans, poses a significant threat to potato (Solanum tuberosum) crops worldwide, impacting their quality as well as yield. Here, we aimed to investigate the potential use of cinnamaldehyde, carvacrol, and eugenol as control agents against P. infestans and to elucidate their underlying mechanisms of action. To determine the pathogen-inhibiting concentrations of these three plant essential oils (PEOs), a comprehensive evaluation of their effects using gradient dilution, mycelial growth rate, and spore germination methods was carried out. Cinnamaldehyde, carvacrol, and eugenol were capable of significantly inhibiting P. infestans by hindering its mycelial radial growth, zoospore release, and sporangium germination; the median effective inhibitory concentration of the three PEOs was 23.87, 8.66, and 89.65 µl/liter, respectively. Scanning electron microscopy revealed that PEOs caused the irreversible deformation of P. infestans, resulting in hyphal shrinkage, distortion, and breakage. Moreover, propidium iodide staining and extracellular conductivity measurements demonstrated that all three PEOs significantly impaired the integrity and permeability of the pathogen's cell membrane in a time- and dose-dependent manner. In vivo experiments confirmed the dose-dependent efficacy of PEOs in reducing the lesion diameter of potato late blight. Altogether, these findings provide valuable insight into the antifungal mechanisms of PEOs vis-à-vis late blight-causing P. infestans. By utilizing the inherent capabilities of these natural compounds, we could effectively limit the harmful impacts of late blight on potato crops, thereby enhancing agricultural practices and ensuring the resilience of global potato food production.

The major component of cinnamon oil as a natural substitute against Fusarium solani on Astragalus membranaceus.

AIMS: Root rot caused by Fusarium solani is an important disease seriously affecting the yield and quality of Astragalus membranaceus. Therefore, this study was performed to elucidate the antifungal activities and mechanisms of cinnamaldehyde treatment against F. solani and its control effect for A. membranaceus root rot. METHODS AND RESULTS: Cinnamaldehyde significantly inhibited mycelial growth and spore germination of F. solani in dose-dependent, and the median effective concentration was 178.68 µl l-1 . Furthermore, scanning electron microscopy, propidium iodide staining, cell leakage experiments and ergosterol quantitation illuminated that cinnamaldehyde could alter the mycelial morphology, damage the plasma membrane and hinder the biosynthesis of ergosterol. Besides, cinnamaldehyde induced the generation of reactive oxygen species by synergistically upregulating the genes encoded subunits for NADPH oxidase. The disease suppression efficacy of 600 µl l-1 cinnamaldehyde against A. membranaceus root rot was 92.98 ± 6.08% (p < 0.05) under greenhouse conditions. CONCLUSIONS: This study proved that cinnamaldehyde could markedly inhibit the growth of F. solani in vitro and effectively suppress the occurrence of A. membranaceus root rot, perhaps by inducing oxidative damage, which results in the distortion of F. solani, and the destruction of cell membrane integrity and permeability. SIGNIFICANCE AND IMPACT OF THE STUDY: This study first explores the antifungal mechanisms of cinnamaldehyde against F. solani in vivo and vitro, thereby providing a promising candidate for disease biocontrol.