In vitro and in vivo activities of eugenol against tobacco black shank caused by Phytophthora nicotianae.

Phytophthora nicotianae causes serious black shank disease in tobacco. Syringa oblata essential oil and its main components were evaluated to develop an effective and environmentally friendly biocontrol agent. Eugenol, which exhibited the strongest activity, was intensively investigated in vitro and in vivo. The mycelial growth of P. nicotianae was inhibited by eugenol at a minimum inhibitory concentration of 200μgmL-1, and inhibition occurred in a dose-dependent manner. Extracellular pH and extracellular conductivity results indicated that eugenol increased membrane permeability. Flow cytometry and fluorescent staining results further showed that eugenol disrupted mycelial membranes but did not affect spore membrane integrity. The in vivo results confirmed that treatment of tobacco with various concentrations of eugenol formulations reduced disease incidence and better controlled against the disease. Our results suggested that the ability of eugenol to control tobacco black shank depended on its ability to damage mycelial membranes and that eugenol formulations have potential as an eco-friendly antifungal agent for controlling tobacco blank shank.