A Preliminary Study of the Response of Microcyclosporella mali to Selected Essential Oils.

In Poland, the main causal agent of sooty blotch and flyspeck disease is the fungus Microcyclosporella mali J.Frank, Schroers et Crous, which is most commonly isolated from the spots found on apples. The aim of the paper was to study the effects of essential oils extracted from Greek oregano, thyme and costmary on M. mali. Analysis of the essential oils was conducted using gas chromatography-mass spectrometry (GC-MS) with a flame ionization detector (FID). The Greek oregano essential oil was classified to the carvacrol chemotype, while the thyme and costmary were classified to the thymol and the β-thujone chemotypes, respectively. The influence of these essential oils on the viability of the M. mali conidia was analysed cytometrically. The Greek oregano oil was characterised by the significantly highest activity against the M. mali spores. The regression analysis performed showed the occurrence of a significant linear relationship between the viability of the conidia and the concentration of the essential oils, which was then the basis for the determination of MICs and MFCs. The values of these parameters in the case of the Greek oregano oil were 0.9 and 0.4%, respectively, and for the thyme oil they were 1.2 and 2.4%.