a b s t r a c tAim: Stilbenes are a group of polyphenols that contribute to the defense mechanisms of grapevine under stress conditions. The main active compounds are oligomeric stilbenes. The sourcing of such compounds is limited by plant raw material availability. In order to overcome this limitation, we proceeded to hemisynthesis of oligomeric stilbenes from natural resveratrol by oxidative coupling using metals. The reaction mixture and the obtained pure compounds were tested for their antimicrobial activity in vitro against P. viticola and B. cinerea, and compared with that of resveratrol and grapevine cane extract. Methods and results: Hemisynthesis was achieved in methanol using silver acetate (AgOAc) as oxidative coupling reagent. Four main compounds were obtained in the reaction mixture: δ-viniferin, parthenostilbenin B, oxistilbenins A and B. Results demonstrate the ability of oxidative coupling reaction to produce potent inhibitors of P. viticola and B. cinerea. The reaction mixture is enriched in antimicrobial compounds with high potency as it is at least eight times more active than grapevine cane extract against P. viticola. In addition, this reaction mixture reveals a high fungitoxicity against B. cinerea in contrast to the grapevine extract. Conclusion: The present findings indicate that metals could be used for producing highly antimicrobial compounds from natural resveratrol. Significance and impact of the study: In this study, a method to produce active dimeric stilbenes to protect grapevine was developed based on botanical ingredients. The combination of natural extracts, rich in resveratrol, and metals such as copper may be used as alternatives to Bordeaux mixture and chemical fungicides to protect crops. k e y w o r d s resveratol, stillbene, hemisynthesis, grey mould, mildew
Natural extracts, and particularly plant by-product extracts, can represent an eco-friendly alternative to synthetic pesticides to control crop diseases. We produced an extract from a mix of grapevine trunk and roots that contain a high amount of complex stilbenes (grapevine phytoalexins), especially ε- and r-viniferins. This extract conferred protection to grapevines against Plasmopara viticola (the causal agent of downy mildew) by displaying antimicrobial activities towards zoospore mobility and sporulation and by stimulating plant defences. From the perspective of its application in the field, a formulated preparation of the extract was proposed using polysorbate and sophorolipids. The formulated extract reduced the development of various oomycetes impacting grapevine, potato, tomato and melon in semi-controlled conditions. Thus, such grapevine extract constitutes a promising strategy to protect major cultivated plants against downy mildews.
Grapevine canes are vine growing byproducts studied for their antimicrobial activities. These properties are directly connected to the stilbene content; oligomeric stilbenes being the most active. In this study, we propose a chemical process, based on oxidative coupling, using metals to increase the oligostilbene rate and the biological effectivity of cane extract against grapevine pathogens. A total of ten compounds were obtained and identified by combining LCMS and NMR spectroscopies, including four newly reported compounds: trans-oxistilbenin C, trans-oxistilbenin D, and cis- and trans-oxistilbenin E. The extract and the main stilbene formed were evaluated for their preventive effects on Plasmopara viticola and Botrytis cinerea growth. The processed extract was highly effective against both pathogens.
Grapevine co-products, as canes, represent a source of compounds of interest to control vineyard diseases with a sustainable approach. We chose to study an extract that we produced from grapevine trunk and roots. This extract, enriched in complex stilbenes, strongly reduced mycelial growth and spore germination of Botrytis cinerea, the fungal agent causing gray mold. The most active stilbenes were resveratrol, r-viniferin, and ε-viniferin. This grapevine extract also inhibited the production of Botrytis laccases. Conversely, Botrytis secretome metabolized resveratrol into δ-viniferin and pallidol (2 dimers); and ε-viniferin, a dimer, into hopeaphenol, r-viniferin, and r2-viniferin (3 tetramers). r-Viniferin and hopeaphenol (2 tetramers) were not metabolized. The biotransformed extract maintained an effective antimycelial activity. This study provides evidence that a grapevine extract enriched in oligomerized stilbenes exerts different anti-Botrytis activities, notwithstanding the ability of the fungus to metabolize some stilbenes.
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