Effectiveness of bulb extracts of Allium species on some selected plant pathogenic fungi

The antimicrobial activity of Allium species has been recognized since a long time, with allicin, further thiosulphinates, and their transformation products having antimicrobial activity. As a last aspect of all investigations, the sulphur chemistry of Allium species located in South West and Middle Asia is much more complex and diverse than the chemistry of those species which were traditionally used in the Western World. Allium volatile compounds of the species from Asia seem to be an excellent source for new sulphur compounds and aroma constituents.

The purpose of this study was to determine and compare the antifungal activity (Minimum Inhibitory Concentration) of Allium sativum L., A. cepa L., A. stipitatum Regel, A. atroviolaceum Boiss. and miconazole (positive control) on Aspergillus flavus, A. niger, Penicillium digitatum, P. italicum and Mucor hiemalis, using broth micro-dilution susceptibility testing method, disk diffusion method, PDA micro-dilution susceptibility testing method and double-dish chamber.

Different concentrations of Allium extraction using ethyl acetate dissolved in DMSO were tested on all the above mentioned fungi, thus A. sativum (garlic) showed the highest antimicrobial effect against all the tested fungi (MIC ≥0.3gr/ml; related to dried total extract) followed by A. cepa (onion) and A. stipitatum (MIC ≥1gr/ml) and then A. atroviolaceum (MIC ≥2.5gr/ml). The MIC of miconazole as a control was ≥0.04mgr/ml.

From the fungal point of view, P. italicum showed the highest susceptibility, while M. hiemalis and A. flavus demonstrated more resistancy towards Allium extracts and Miconazole. Meanwhile A. sativum inhibited A. niger more than Miconazole, while having only little effect on P. digitatum.

The results indicate that extractions of Allium spp. have antifungal activity and might be promising, at least, in 'biological' treatment of fungal-associated plant diseases.