Essential oil of Chrysanthemum indicum L.: potential biocontrol agent against plant pathogen Phytophthora nicotianae.

Phytophthora nicotianae is currently considered one of the most devastating oomycete plant pathogens, and its control frequently relies solely on the use of systemic fungicides. There is an urgent need to find environment-friendly control techniques. This study examined the chemical composition, inhibitory activity, and possible modes of action of the essential oil of Chrysanthemum indicum L. (EOC) flower heads against P. nicotianae. The EOC was obtained using hydrodistillation at a 0.15% yielded. It inhibited mycelial growth and spore germination of P. nicotianae at a minimum inhibitory concentration (MIC) of 200 μL/L, and exhibited fumigation effects (92.68% inhibition at 157.48 μL/L). Marked deformation of P. nicotianae mycelia included deformed tip enlargement, shrinkage, and rupture. Further, 55 and 47 compounds were identified using gas chromatography-mass spectrometry (GC-MS) and headspace solid-phase microextraction (HS-SPME) GC-MS analyses, representing 88.2% and 98.91% of the total EOC, respectively. Monoterpenes (25.77%) and sesquiterpenes (54.14%) were the major components identified using GC-MS, whereas monoterpenes were the main constituents in the HS-SPME GC-MS analysis. The higher proportions of sesquiterpenes and monoterpenes could be responsible for the inhibitory activity of EOC, which increased mycelia membrane permeability and the content of mycelial malondialdehyde (MDA) in a dose-dependent manner. Cell death also occurred. Thus, destruction of the cell wall and membrane might be two modes of action of EOC. Our results would be useful for the development of a new plant source of fungicide for P. nicotianae-induced disease.