Biological Fumigation

The production of volatile antibiotics is rare among microorganisms and has been reported only in a few soilborne organisms such as Trichoderma spp. and Bacillus spp. [32,33]. A recently discovered fungus, Muscodor albus, produces about 28 volatile compounds, mainly alcohol, ester, ketone, and acid derivatives, which together can inhibit or kill fungi, bacteria, and oomycetes [34]. The fungus, which was isolated from a cinnamon tree in Honduras, was described as a new genus and is related to endophytes of the family Xylariaceae (Ascomycetes) [35]. Recently, the possibility of controlling postharvest decay by biological fumigation with M. albus was demonstrated by Mercier and Jimenez [36]. Biofumigation was performed passively by placing a grain culture of the fungus in the presence of inoculated fruits. Diseases controlled by such biofumigation treatment were gray mold of apples and grapes, caused by Botrytis cinerea, blue mold of apples, caused by Pénicillium expansum, brown rot of peaches, caused by Monilinia fructicola, and green mold and sour rot of lemons, caused by P. digitatum and Geotrichum citri-aurantii, [36,37]. Several storage pathogens belonging to species of botrytis, colletotrichum, geotrichum, monilinia, penicillium, and rhizopus were also killed in vitro by exposure to volatile compounds produced by a potato dextrose agar colony of M. albus [36]. This suggests that pathogens are not merely inhibited but are killed in fruit wounds. In some cases, there was effective decay control when biofumigation was performed 24 hours after inoculation. Fumigation at low storage temperature was also effective in grapes [37] and apples (J. Mercier, unpublished data). Besides controlling postharvest decay, biofumigation with M. albus also reduced populations of pathogenic bacteria such as Escherichia coli O157:H7, salmonella serotypes, Shigella spp., and Listeria monocytogenes on the surface of cucurbit and tomato fruits [38]. Biofumigation treatment with M. albus would be applicable to different stages of storage and shipping in most commodities. It could also be used with commodities that are too fragile to be handled or to receive a liquid fungicide treatment, such as strawberries or grapes. Exposure to the volatiles does not cause any off-flavor of the treated produce in informal taste tests. There were no detectable volatile compounds in the skin of any fruit tested (apples, peaches).

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