Impact of Ecklonia maxima seaweed extract on the vegetative, reproductive and microbiome in Vitis vinifera L. cv Cabernet-Sauvignon

Abstract

Context and purpose of the study. Climate change is a major challenge in wine production. It results in erratic weather conditions which may lead to a reduction in grape yield and the subsequent grape and wine quality. Fungal disease pressures also increase because of the prevailing weather conditions. Conventional grape production relies heavily on the use of synthetic and agrochemicals and fertilisers to ensure sustained growth, yields and disease management. The application of these products poses negative impacts on human health and environment. This necessitates the move towards agricultural sustainability. Biostimulants are considered environmentally friendly and cost-effective alternatives to synthetic fertilisers and crop protection products. Seaweed extracts are the most defined non-microbial biostimulants use on commercial crops in literature. Several studies investigated the use of Ascophyllum nodosum (L.) Le Jolis. Although, positive effects were reported on the use of this specie little is known on the impact of an indigenous seaweed specie int he Cape South Coast – Ecklonia maxima specie as a mitigation strategy to abiotic stress.

Material and methods. Site selection. An 18-year-old Vitis vinifera L.cv. Cabernet Sauvignon clone 339C grafted on 101-14 Mgt vines planted with 2.5 m x 2 m row and vine spacing and trained on a Vertical Shoot Positioning (VSP)/ 3-wire trellis system during the 2021-2022 season. The site was subjected to drip irrigation with drippers spaced at 1 m, delivering an average of 2.3 L/ha. A random block design, with two factors: Ecklonia maxima (EM) Kelpak® foliar application and water status scenario (non-irrigated and irrigated). The experimental site consisted of 120 vines, allocated to 40 mini-experimental plots (consisting of 3 vines each) which were randomly assigned throughout the vineyard.

Leaf surface area, classical parameters and grapevine yield.

Leaf area was determined at three phenological stages: véraison (E-L 35), mid-ripening (E-L 37) and post-harvest (E-L 39) using image acquisition techniques as described by Glozer (2008). MATLAB (The MathWorks, Inc., Natick, Massachusetts, United States) was used for individual image segmentation and ImageJ (Rasband, W.S., ImageJ, U. S. National Institutes of Health, Bethesda, Maryland, USA) was used to calculate the area of each leave in cm². Classical parameters (sugars, pH and titratable acidity-TA) were measured on a weekly basis from véraison until harvest. During dormancy, canes were counted, pruned and the weight measured.

Microbiome – Leaf and berry

Leaves and berries were collected at pea-size (E-L 31), véraison (E-L 35) and harvest (E-L 38) for each treatment between the morning and afternoon sun sides. Three biological replicates were sampled per vine for the leaf microbiome. Three berries were sampled from the top, middle and bottom of bunches from both morning and afternoon sun sides per vine/per treatment. Leaf and berry samples were washed with 100 mL phosphate-buffered saline (PBS) isotonic solution under gentle agitation for one hour and the wash solution containing microbial biomass was stored at -20°C until DNA extraction.

DNA Extractions & Bacterial and fungal rRNA amplicon sequencing

The ZymoBiomics DNA miniprep kit (Zymo Research, United States) was used for extraction of total genomic DNA (Papageorgiou, 2023). For the bacterial community 16S sequencing, the V2-V9 hypervariable regions, were amplified and sequenced, while for the fungal community the ITS1-5.8S rRNA gene region, was targeted. Briefly, the DNA quality was assessed with spectrophotometry to ensure an abundance ratio of 260/280 between 1.8 and 2.0 and 260/230 ratio above 1.0. For the fungi, the universal primers ITS1F (5’-CTTGGTCATTTAGAGGAAGTAA-3’) and ITS2 (5’-GCTGCGTTCTTCATCGATGC–3’) were used to amplify the ITS1 region.

Results. Leaf area consistently increased when treated with Ecklonia maxima from E-L 25 to E-L 41. No significant differences were seen between the treatments. Berry mass was positively influenced by the Ecklonia maxima and water regime applied. Sugar content was significantly (p≤ 0,05) higher in the Ecklonia maxima treated grapevines. No significant differences were observed in the pH and TA at harvest.

Ecklonia maxima applications increased the abundance of Staphylococcus, Lactobacillus and Alloiococcus on the leaves, berries and must, which inhibit pathogens and exhibit biocontrol properties. The presence of Lactobacillus was favouarable for the completion of malolactic fermentation and clarification of the wine. Mycotoxin producing bacteria, Penicillium and Alternaria, were more prevalent in non-irrigated berries and grape must, however, were reduced in EM-treated samples. Botrytis and Erysiphe are harmful grapevine pathogens that were diminished on the Ecklonia maxima sprayed leaves and berries.