Antifungal Activity of the Essential Oil of Hyssop (Hyssopus officinalis)

The antifungal and fungicidal e€ects of hyssop (Hyssopus ocinalis) oil and its individual components were studied in a series of in vitro and in vivo experi- ments. Mycelial growth of the plant pathogenic fungi Pyrenophora avenae and Pyricularia oryzae was com- pletely inhibited by 0.4% hyssop oil. Volatile compo- nents di€using from agar medium containing 0.4% hyssop oil also completely inhibited the growth of these two fungi. Various components of hyssop oil (L-bornyl acetate, isopinocampheol and pinocamphone), used individually, reduced growth of P. avenae and, where combinations of individual components were used, any mixture containing isopinocampheol completely inhib- ited fungal growth. Growth of P. oryzae was less a€ected by individual components of the oil. Hyssop oil reduced germination of Botrytis fabae conidia and uredospores of Uromyces viciae-fabae, but in contrast to the data from in vitro experiments, its e€ects on pathogen infection were less clear cut. Thus, although 0.05% hyssop oil reduced rust infection of broad bean when applied 1, 2 or 3 days before, or 1 or 2 days after inoculation, its e€ects against barley powdery mildew and apple powdery mildew were variable. It is suggested that this variability might be the result of the volatile components of the oil di€using away from leaf surfaces, thus reducing the concentration of active components on the leaf surface.