Volatile organic compounds: a role in elicitor-induced resistance of grapevine against pathogens?

As Vitis vinifera varieties are susceptible to fungal diseases, numerous chemical treatments are generally required to ensure the quantity and quality of the harvest. However, in the context of sustainable viticulture, there are increasing societal request, political incitation, and winegrowers’ awareness to reduce the use of pesticides. Among possible solutions the use of elicitors that could be included in integrated pest management or biocontrol strategies might be very promising. These bioactive compounds are able to trigger plant defences, leading to induced resistance (IR) against pathogens. Despite IR can be elicited very successfully in controlled environments; it is in most cases not effective enough in practically controlling disease in the vineyard.

To obtain a comprehensive understanding of IR and to identify molecular markers enabling the identification of factors (physiological, environmental…) that can impact IR efficacy in the vineyard we performed a transcriptomic analysis under controlled conditions. The results indicated that among highly up-regulated genes associated to IR, one was annotated as terpene synthase, suggesting that terpenes could be emitted following elicitor treatment. This prompted us to investigate whether IR elicitors actually induce the production of volatile organic compounds (VOCs). Applying online analysis (PTR-QMS) of VOC emissions in dynamic cuvettes and passive sampling in gas tight bags with solid phase micro extraction (SPME / GC-MS), we followed the emission of VOCs of vines in response to elicitor-IR against downy mildew under controlled greenhouse conditions.

The results obtained point out some of them as potential markers of elicitor-IR (as trans a-farnesene) whereas MeSA is rather a marker of downy mildew infection.