The Influence of Essential Oils on Developmental Structures and Morphology on the Yeast Pathogen Eremothecium ashybii

Introduction: Essential oils possess antimicrobial properties as a result they can be used as bio-preservatives and to control crop contamination thereby ensuring food safety. Contamination of food products by fungi affects shelf life, influences food safety negatively and frequently results in qualitative and quantitative losses of food commodities. The search for alternative antifungals to reduce commodity losses due to fungal contamination post-harvest and infections of plants on farms is currently in demand.

Purpose: The current study investigated the influence of essential oils on growth and morphology of the yeast pathogen Eremothecium ashbyii.

Methods: Essential oils (Bergamot, citronella, eucalyptus, rosemary, rose geranium, sage, tea tree and thyme) were characterized using Gas Chromatography Mass Spectrometry. The agar diffusion assay together with light and scanning electron microscopy were used to study the influence of essential oils on growth and morphology of E. ashbyii.

Results: Bio-assay results showed that oils characterized by a high content of monoterpenes showed higher antifungal activity while oils characterized mainly by oxygenated monoterpenes displayed weak activity. Furthermore, tested oils affected yeast growth by first targeting developmental structures (asci and ascospores) with increased mitochondrial activity, indicating their possible anti-mitochondrial activity. Microscopy revealed that oils mainly characterized by a high content of monoterpenes completely inhibited developmental structures or affected their development whereas hyphae appeared granular and wrinkled. 

Significance: The current study successfully exposed that tested oils can be used to develop alternative novel biological anti-germination agents to combat the spread E. ashbyii and possibly other fungal plant pathogens.