ABSTRACT Natural aroma volatile compounds from plants, and structurally analogous compounds, are known to both stimulate and inhibit spore germination and vegetative growth of plant pathogenic and other fungi. Among the compounds which exhibit activity are aldehydes, alcohols, ketones, acids, amines and those belonging to several additional chemical classes. Fungal genera affected include Puccinia, Uromyces, Botrytis, Monilinea, Penicillium, Aspergillus, Alternaria, and numerous others. In addition to their activity influencing fungal spore germination and vegetative growth, aroma compounds have also been shown to stimulate and inhibit germination of pollen. Wound volatile compounds emitted by damaged leaves and other plant materials were found to be among the most inhibitory natural compounds bioassayed. These compounds are derived from the lipoxygenase-hydroperoxide lyase pathway and are largely comprised of the aldehydes, Z-3-hexenal, E-2-hexenal, and hexanal, and their corresponding alcohols. Tests using natural volatile compounds as fumigants to control fungi, primarily Botrytis, on strawberries and table grapes showed numerous compounds were effective for this purpose including E-2-hexenal. However, strawberries absorbed and frequently metabolized the fumigants and thus compound effectiveness was likely mitigated. In contrast, table grapes exhibited a lower tendency for fumigant absorption and E-2-hexenal significantly reduced Botrytis development on grapes for up to 12 weeks in cold storage. The organoleptic and safety aspects of potentially useful compounds remain to be evaluated. Furthermore, low concentrations of certain compounds in the vapor phase (>0.5 μmole/L of air for E-2-hexanal) can stimulate fungal growth in some instances. This aspect of the interaction of volatile compounds with fungal pathogens needs to be further investigated to determine if endogenous aroma compounds at natural concentrations can influence pathogen development on plant-derived foods. Collectively, the experimental observations relating to the action of volatile compounds from plants on fungal growth and development indicate that exogenous application of these compounds through fumigation, and perhaps, eventually, alteration of their endogenous concentrations will offer alternative methods for control of economically important diseases of plant-derived foods.
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