Effects of oil extracts of Eupatorium adenophorum on Phytophthora capsici and other plant pathogenic fungi in vitro.

The antifungal activity of oils extracted from Eupatorium adenophorum was tested against five phytopathogens in vitro. Oil extracts inhibited the mycelial growth of Phytophthora capsici which causes phytophthora blight in pepper. The minimum inhibitory concentration of oils against P. capsici was 500μg/ml after 7days incubation. At the ultrastructural level, oil extracts caused complete disorganization of intracellular organelles, cytoplasm depletion, disruption of cytoplasmic membranes and the cell wall. Membrane permeability increased with the increasing concentration of oil extracts. These results suggested that these oil extracts exhibited multiple modes of action including disruption of the cell membrane system. Furthermore, oil extracts combined with synthetic fungicides synergistically inhibited mycelial growth of P. capsici, which creates the possibility of reducing fungicide concentration needed to successfully control phytophthora blight in commercial pepper production. This study's use of multiple methods of analysis has increased our understanding of the mode of action of E. adenophorum oil extracts against P. capsici.