Institute for Medicinal Plant Research “Dr Josif pančić” , Belgrade , Serbia
Biological control involves the use of beneficial microorganisms (bacteria, yeasts, fungi) or the products of their metabolism, as well as the application of plant extracts and essential oils as alternative measures in plant protection. Examining over 40 stored dried medicinal plant species the lowest microbial quality were determined for corn silk, mint herb and leaf, nettle leaf, horsetail herb and marigold flower. Although mixed infections was recorded with different types of fungus the Fusarium was noted as the most dominant genera for most tested drugs, followed by Aspergillus and Alternaria. In order to find an effective biological control agent, we investigated the possibility of applying the 22 essential oils and 14 isolates of Bacillus sp. in the control of selected identified fungi. All tested essential oils showed antifungal activity on pathogenic fungi isolated from herbal drugs, but with varying degrees of inhibitory activity. Savory, oregano and thyme oil, with phenols as the dominant component, were the most effective, while vetiver oil, and those from Citrus species, with dominant monoterpen hydrocarbons, were the least effective against pathogenic fungi. According to the results of tested synergistic activity of selected essential oils, combination of essential oils exhibited better antifungal activity than when they were tested individually. Using in vitro, dual cultivation assay, Bacillus sp. isolates showed various degree of antagonistic activity against different types of plant pathogenic fungi. The best antagonism showed isolates SS-12.6, SS-13-1, SS-27.7, SS-38.3, SS-38.4 and SS-40.2, as well as lipopeptide extract isolated from Bacillus sp. SS-12.6. Isolates were more effective in the presence of selected essential oils, than when tested individually, with particular exceptions. Based on the results obtained in this work we conclude that the essential oils of savory, oregano, thyme and roses, as well as Bacillus sp. isolate SS-12.6 and its lipopeptide extract, represent a good basis for the formulation of products with potential efficacy in the control of plant pathogenic fungi, either in preventing the contamination in the field, or via indoors decontamination.
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