Oregano essential oils prime plant immunity to fight downy mildew

by | Oct 31, 2019 | South Africa Wine Scan

In this study, researchers wanted to better understand how essential oils (EO) can help to protect grapevines against downy mildew. Essential oils (EO) are considered promising compounds for use in plant protection as studies have indicated their antibacterial, antiviral and antifungal properties on numerous crops. The challenge is that their efficiency is dependent on factors such as timing of application, application methods and interaction between the host, the pathogen and the essential oil (EO).


  • Researchers wanted to determine: Whether continuous fumigation of grapevines with EO can control downy mildew. Through fumigation, some of the challenges regarding direct application could be avoided. What mechanisms were triggered inside the plant and the pathogens when exposed to EO. Whether EO represses downy mildew oomycetes or primes plant resistance.
  • A custom-built chamber was used. This chamber allowed for continuous fumigation of potted vines with different EO.
  • The Chasselas variety was used because it is extremely susceptible to downy mildew.
  • Grapevines were infected with downy mildew after which they were exposed to continuous fumigation with different EO, at different concentrations. Two different durations of fumigation were also tested.
  • When infection symptoms were detected on leaves of control plants, experiments were ended.
  • Plant physiology (photosynthesis and growth rate parameters) were recorded and leaves were sampled at different time points for subsequent RNA extraction and transcriptomics analysis.


  • Oregano vulgare EO vapour treatment was the most effective and reduced downy mildew development by 95%.
  • Transcriptomic data clearly indicated that treatment with EO triggered the plant’s intrinsic immune system. Including genes involved in salicylic, jasmonic acid and ethylene synthesis and signaling, activating Pathogenesis-Related-proteins as well as phytoalexin synthesis.
  • This is the first research that truly explains how EO, the pathogen and the host interact. It proved that EO are strong antifungal agents because of the way they trigger resistance pathways inside grapevine plants.


Downy mildew is one of the most significant grapevine diseases which necessitates the use of fungicides. Due to increased environmental awareness and pressure from consumers, finding biological solutions to fungicides are essential.  Even though continuous fumigation of grapevines is not practical in-field, the results from this project gives valuable insights and knowledge. The information is critical to aid in further research into the production of biopesticides, plant stimulation products and for resistance-breeding strategies.

Link to article: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0222854

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