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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 experiments. Mycelial growth of the plant pathogenic fungi Pyrenophora avenae and Pyricularia oryzae was completely inhibited by 0.4% hyssop oil. Volatile components 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 inhibited 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€ffects 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€ffects 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.