&lt;em&gt;Vitis vinifera&lt;/em&gt; canes, a source of stilbenoids against downy mildew

Tristan Richard,Jean-Michel Mérillon,Xavier Vitrac,Pierre Waffo Teguo,Assia Abdelli-Belhad

doi:10.20870/oeno-one.2016.50.4.1178

Abstract

Aim: To investigate the antifungal efficacy of grape cane extracts enriched in stilbenes against Plasmopara viticola by in vivo experiments on grape plants.Methods and results: Experiments on grape plants were carried out from 2007 to 2008 at commercial vineyards in « Le Tourne » (southwest region of France) on Vitis vinifera L. cv Merlot plants and in a greenhouse, where 45-day-old plants (Merlot) were used. Grapevine plants were treated with stilbene extract (STE) or « Bordeaux mixture » (BM) as positive control. STE, prepared from Vitis vinifera canes, contained 33% of total stilbenes ranging from monomers to tetramers and was used at 5 g L-1. The degree of protection against downy mildew was determined as the percentage of infected leaf surface area and pathogen attack frequency. On young plants in greenhouse, P. viticola inoculation and three treatments with STE were carried out. After the treatments, the disease reduction was from 59 to 69% for pathogen attack frequency and from 83 to 88% for infected leaf surface for the two modes of infestation (artificial and secondary). STE triggered a similar intense decrease in downy mildew infection as recorded for BM. In the vineyard assay, downy mildew infection was allowed to occur naturally. Field grown plants were treated every 7th day for eight weeks or every 14th day for eight weeks during June and July. We observed that STE was also able to prevent P. viticola infection in vineyard but to a lesser extent. Treatment with STE every 7th day provided better results in terms of infection frequency and infected leaf area than that every 14th day. STE treatment of plants every 7th day in vineyard reduced the frequency of attack by 16 to 39% and leaf surface infection by 57 to 61%, which was lower than that recorded for BM. STE also displayed in vitro inhibitory effects on the release of zoospores from sporangia and the germination of zoospores of P. viticola. Zoospore germination was completely inhibited at a concentration of 100 mg L-1 and zoospore release was inhibited at 330 mg L-1.Conclusions: Treatment of young grapevine plants in greenhouse with stilbene extract from grapevine canes offered considerable protection against P. viticola that was identical to that provided by Bordeaux mixture. STE was also able to prevent P. viticola infection in vineyard but to a lesser extent. Treatment with STE every 7th day in vineyard provided better results than that every 14th day.Significance and impact of the study: Stilbenes from grapevine canes are good candidates as natural fungicides against downy mildew. Given the very large quantity of grape canes available each year, this strategy could be scaled up to control this grapevine disease in a sustainable manner.

Highlights

Downy mildew caused by an oomycete, Plasmopara viticola, is one of the most destructive diseases in vineyards
Treatment of young grapevine plants in greenhouse with stilbene extract from grapevine canes offered considerable protection against P. viticola that was identical to that provided by Bordeaux mixture
stilbenoid extract (STE) was able to prevent the infection of P. viticola in vineyard but to a lesser extent

Summary

Introduction

Downy mildew caused by an oomycete, Plasmopara viticola, is one of the most destructive diseases in vineyards. Protection against it involves several applications of fungicides between budburst/sprout and fruit-ripening depending on the disease severity and the climatic conditions of the year (Schnee et al, 2013). These pesticides have a harmful impact on the environment as well as on human health. Developing alternative strategies such as the use of natural products from plants that are biodegradable and usually less toxic has become a pressing need. The alternative approach is to find elicitor compounds for grapevine defense stimulation, but only a few commercial products with low efficacy have been approved for this purpose (Aziz et al, 2003; Saigne-Soulard et al, 2015)

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