ANTIFUNGAL ACTIVITY OF OREGANO AND THYME ESSENTIAL OILS APPLIED AS FUMIGANTS AGAINST FUNGI ATTACKING STORED GRAIN

Essential oils from oregano and thyme were applied for 24 h as fumigan ts against the mycelia and spores of Aspergillus flavus, Aspergillus n iger and Aspergillus ochraceus, as well as against natural microflora of wheat grains. The minimal inhibitory concentration (MIC) of oregano oil needed to inhibit the mycelial growth of the fungi was 2.0 mu l/L , while spores were eradicated following exposure to 2.0 to 2.5 mu l/L . The thyme essential oil was less efficient in controlling mycelia an d growth was observed even following exposure to 4.0 mu l/L. However, the thyme essential oil was fungitoxic to spores (MIC=3.0 mu l/L). In another set of trials the efficacy of the oils and two of their consti tuents (carvacrol and thymol) in controlling natural microflora of sur face-sterilized wheat grain was studied. Of the four materials investi gated, only oregano essential oil exhibited fungicidal activity and, f ollowing 24 h exposure to 20 mu l/L, a significant reduction in the pe rcent of infested grain was observed even after 5 days of incubation o n potato dextrose agar. A reduction in the germinability of the grains was evident following exposure to the materials tested. When the fung icidal activity of oregano essential oil was evaluated using grains wi th different moisture contents (MC), data revealed that the better inh ibitory effect was achieved in grain with a high MC. The findings emph asize the toxicity of oregano and thyme essential oils as fumigants ag ainst fungi attacking stored grain and strengthen the possibility of u sing them as an alternative to chemicals for preserving stored grains.