Additive and synergistic antifungal effects of copper and phenolic extracts from grape cane and apples.

BACKGROUND: Organic viticulture seeks sustainable alternatives for eco-toxic copper fungicides to control downy mildew caused by Plasmopara viticola. (Poly)phenol-rich extracts of agricultural byproducts are known to possess antifungal activity, but high production costs often limit their actual implementation. RESULTS: We developed and produced novel ligninsulfonate-based grape cane extract (GCE) formulations and an apple extract on a pilot plant scale, including a detailed (poly)phenol characterization by high-performance liquid chromatography photodiode array mass spectrometry (HPLC-PDA-MS). Our GCE formulations alone reduced downy mildew disease severity in greenhouse trials by 29%-69% in a dose-dependent manner, whereas a standard application of the copper-based agent alone reached ~56%. When applied together, disease severity was diminished by 78%-92%, revealing a synergistic effect that depended on the mixture ratio. Combining GCE formulations with the apple extract, additive effects were found (80% disease severity reduction). CONCLUSION: The studied plant extracts are proposed to both substitute for and synergistically reinforce copper fungicides in grapevine downy mildew control. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Variability of Constitutive Stilbenoid Levels and Profiles in Grape Cane (Vitis vinifera L.) Depending upon Variety and Clone, Location in the Vineyard, Pruning Time, and Vintage.

Stilbenoids in grape cane (Vitis vinifera L.) are bioactive compounds relevant for plant defense and the potential valorization of this byproduct. Our screening of grape cane from 102 varieties showed constitutive stilbenoid levels in a wide range (557-7748 mg/kg of dry weight). Analyses of genetically distinct clones of selected cultivars unraveled that intravarietal variability (e.g., cv. Riesling, 3236-6541 mg/kg) was higher than that across samples from a single clone but different vineyard positions (3017-3710 mg/kg). Furthermore, stilbenoid levels in samples obtained in October, December, and February (3 years, 2017-2019) showed pronounced quantitative and qualitative variability and the highest yields upon December pruning. For instance, vitisin B and ε-viniferin in cv. Pinot Noir and Accent were predominant in 2017 and 2019 (both >90% of total stilbenoids) but not in 2018 (both <55%) when temperatures were high and precipitation low. In brief, we report the variability of stilbenoid levels in grape cane depending upon genetic and environmental factors.