S20 - Session P3 - Plant defense inducers promoting downy mildew protection on grapevines with distinct pattern of stilbene accumulation and different level of defense gene induction among cultivars

Authors: Amélie Chaigneau *, Caroline Servant , Florian Bryone , Amélie Lamothe, Morgane Desmots, Amélie Siegler , Elisa Thalinger , Caroline Bonneau

The causal agent of downy mildew, Plasmopara viticola of grapevine is responsible of grape yield losses worldwide. Due to non-renewals of anti-mildew fungicides, control of epidemics is becoming a major challenge for winegrowers. Alternative strategies, such as the use of plant defense stimulators (PDI), are being developed. PDIs induce grapevine defense reactions mostly via synthesis of pathogenesis-related (PR) proteins, and accumulation of phytoalexins, both with antimicrobial properties. The most important phytoalexins in Vitaceae are stilbene polyphenols. The aim of this study was to compare PDIs of different compositions, for their ability to induce (i) downy mildew protection (ii) PR gene induction and (iii) stilbene accumulation, on 4 different grapevine cultivars. Plants of grapevine cultivars, Pinot noir, Chardonnay, Chenin and Cabernet Sauvignon were treated in greenhouse with PDIs. Quantification of PR genes and stilbene synthase gene was performed by qPCR using the qPFD® platform. Stilbene accumulation pattern and polyphenol profiles were performed by UPLC on leaves extracts. Downy mildew protection efficiency was assessed on leaf discs artificially inoculated. Results indicated for 2 PDIs a high or moderate level of both protection and induction of PR and STS genes. Level of accumulation of stilbenes correlated with the level of defense gene induction as well as with the level of protection.Analysis of stilbene profiles indicated that levels of trans-resveratrol, piceid and ε-viniferin were differentially induced according to PDIs compounds.Furthermore, the receptivity of the 4 cultivars to PDIs was distinct in term of defense gene expression level and stilbene profiles. Screening PDIs based on defense gene expression level by qPCR is now routinely used. Because stilbene accumulation pattern seems to differ according to PDIs, analysis of stilbene accumulation profile may deliver useful information to develop biocontrol synergistic strategy.