Antisporulating and respiration-inhibitory effects of essential oils on filamentous fungi.

Sporulation of four species of filamentous fungi, namely Aspergillus fumigatus, Fusarium solani, Penicillium expansum and Rhizopus oryzae, was suppressed by gaseous contact with citron, lavender and thyme oils and, to a lesser extent, by that of perilla and tea tree oils. Lemongrass and cinnamon bark oils were scarcely active. The antisporulating effect of the essential oils was not observed when they were applied as a solution, indicating that their vapours were the active form. Moreover, exposure of fungal cultures to vapours of the active essential oils caused curling of the tips of aerial hyphae (R. oryzae) or incomplete development of conidiophores (A. fumigatus). These antisporulating effects of the vapourizing essential oils seemed to be correlated with their respiration-inhibitory activity, rather than with their growth-inhibitory activity.