Journal of Chemical Ecology, Vol. 18, No. 7, 1992 EFFECTS OF SOME NATURAL VOLATILE COMPOUNDS ON THE PATHOGENIC FUNGI Alternaria alternata AND Botrytis cinerea T.R. HAMILTON-KEMP, t'* C.T. McCRACKEN, JR.,1 J.H. LOUGHRIN, 1 R.A. ANDERSEN, 2 and D.F. HILDEBRAND 3 1Department of Horticulture 2U.S. Department of Agriculture, ARS, and Department of Agronomy 3Department of Agronomy University of Kentucky Lexington, Kentucky 40546 (Received December 19, 1991; accepted February 24, 1992) Abstract--A bioassay system was developed to test the effects of volatile compounds on the growth of hyphae from germinating fungal spores. Volatiles from crushed tomato leaves inhibited hyphal growth of two fungal pathogens, Alternaria alternata and Botrytis cinerea. Aldehydes, including C6 and C9 compounds formed by the lipoxygenase enzyme pathway upon wounding leaves, inhibited growth of both fungal species. Terpene hydrocarbons, 2-carene and limonene, had no significant effect on hyphal growth. The quan- tities of volatile compounds in the vapor phase of the bioassay system were measured by direct headspace sampling and GC analysis. Key Words--Headspace, aldehydes, E-2-hexenal, monoterpenes, lipoxygen- ase, spores, hyphae, wounding, Lycopersicon esculentum, Alternaria alter- nata, Botrytis cinerea. INTRODUCTION Previously, we screened foliage from several plant species to evaluate the effects of volatile compounds released from the tissues on pollen germination and growth in vitro (Hamilton-Kemp et al., 1991). Crushed tomato leaves emitted volatiles that were inhibitory, and among these the most active substances detected were unsaturated aldehydes derived from the lipoxygenase pathway [reviews by Gal- liard and Chan (1980) and Hatanaka et at. (1987)]. Since spores from pathogenic fungi may come in contact with volatiles from wounded or damaged leaves, we * To whom correspondence should be addressed. 1083 0098-0331/92/0700-1083506.50/0 9 1992 Plenum Publishing Corporation