<em>Vitis vinifera</em> canes, a source of stilbenoids against downy mildew

Abstract

&lt;p style="text-align: justify;"&gt;&lt;strong&gt;Aim:&lt;/strong&gt; To investigate the antifungal efficacy of grape cane extracts enriched in stilbenes against &lt;em&gt;Plasmopara viticola&lt;/em&gt; by &lt;em&gt;in vivo&lt;/em&gt; experiments on grape plants.&lt;/p&gt;&lt;p style="text-align: justify;"&gt;&lt;strong&gt;Methods and results&lt;/strong&gt;: Experiments on grape plants were carried out from 2007 to 2008 at commercial vineyards in « Le Tourne » (southwest region of France) on &lt;em&gt;Vitis vinifera&lt;/em&gt; 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 &lt;em&gt;Vitis vinifera&lt;/em&gt; canes, contained 33% of total stilbenes ranging from monomers to tetramers and was used at 5 g L&lt;sup&gt;-1&lt;/sup&gt;. 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, &lt;em&gt;P. viticola&lt;/em&gt; 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 7&lt;sup&gt;th&lt;/sup&gt; day for eight weeks or every 14&lt;sup&gt;th&lt;/sup&gt; day for eight weeks during June and July. We observed that STE was also able to prevent &lt;em&gt;P. viticola&lt;/em&gt; infection in vineyard but to a lesser extent. Treatment with STE every 7&lt;sup&gt;th&lt;/sup&gt; day provided better results in terms of infection frequency and infected leaf area than that every 14&lt;sup&gt;th&lt;/sup&gt; day. STE treatment of plants every 7&lt;sup&gt;th&lt;/sup&gt; 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 &lt;em&gt;in vitro&lt;/em&gt; inhibitory effects on the release of zoospores from sporangia and the germination of zoospores of &lt;em&gt;P. viticola&lt;/em&gt;. Zoospore germination was completely inhibited at a concentration of 100 mg L&lt;sup&gt;-1&lt;/sup&gt; and zoospore release was inhibited at 330 mg L&lt;sup&gt;-1&lt;/sup&gt;.&lt;/p&gt;&lt;p style="text-align: justify;"&gt;&lt;strong&gt;Conclusions&lt;/strong&gt;: Treatment of young grapevine plants in greenhouse with stilbene extract from grapevine canes offered considerable protection against &lt;em&gt;P. viticola&lt;/em&gt; that was identical to that provided by Bordeaux mixture. STE was also able to prevent &lt;em&gt;P. viticola&lt;/em&gt; infection in vineyard but to a lesser extent. Treatment with STE every 7&lt;sup&gt;th&lt;/sup&gt; day in vineyard provided better results than that every 14&lt;sup&gt;th&lt;/sup&gt; day.&lt;/p&gt;&lt;p style="text-align: justify;"&gt;&lt;strong&gt;Significance and impact of the study&lt;/strong&gt;: 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.&lt;/p&gt;

A dimeric stilbene extract produced by oxidative coupling of resveratrol active against <em>Plasmopara viticola</em> and <em>Botrytis cinerea</em> for vine treatments

“…The results for the grapevine cane extract are in agreement with Gabaston et coauthors (Gabaston et al, 2017). Grapevine extract effectivity against downy mildew has been demonstrated in vitro (Schnee et al, 2013), in greenhouse and vineyard (Richard et al, 2016). The reaction mixture was eight times more potent than the cane extract, with IC 50 of 23 and 197 mg.L -1 , respectively (Table 2).…”

“…Stilbenes are a group of polyphenols produced in several plants and especially in grapevine Rivière et al, 2012). Under stress conditions as pathogen attacks, stilbenes play the role of phytoalexins and thus are involved in the grapevine defense mechanisms (Gabaston et al, 2017;Langcake and Pryce, 1977;Pezet et al, 2003;Richard et al, 2016;Schnee et al, 2013;Vrhovsek et al, 2012). Among stilbenes, oligomers of resveratrol, such as viniferins, are promising antimicrobial compounds (Gabaston et al, 2017).…”

Vineyard evaluation of stilbenoid‐rich grape cane extracts against downy mildew: a large‐scale study

“…The in vitro protection was maximal over the range 2–8 g L −1 with 95% efficacy. These results were accordance with previous reports on P. viticola inhibition using GCE of different origins . To test the potential of protection under natural conditions, we next tested this GCE in a large‐scale field trial.…”

“…Stilbenoids extracted from V. vinifera L. canes have shown inhibitory activities against P. viticola with the best seen with resveratrol tetramers; hopeaphenol, vitisin A and vitisin B. The potential of grape cane extracts (GCE) to limit downy mildew has been reported in greenhouse experiments and to a lesser extent in vineyards …”

Grapevine Cane Extracts: Raw Plant Material, Extraction Methods, Quantification, and Applications

“…In this sense, grapevine cane extract enriched in stilbenes was suggested for the antifungal treatment of grapevines to prevent the catastrophic consequences of fungal diseases. Richard et al [ 115 ] used Vineatrol against downy mildew in greenhouses and vineyards. At a concentration of 5 g/L, they obtained a comparable effect to that of copper in greenhouses, reducing the frequency of attack by up to 39% and leaf surface infection by up to 61% in vineyards.…”