The characterization of Vitis vinifera L cv. Cabernet sauvignon: the contribution of Ecklonia maxima seaweed extract

Biostimulants and biofertilizers are considered environmentally friendly and cost-effective alternatives to synthetic fertilizers, plant growth regulators and crop improvement products. Broadly, plant biostimulants are expected to improve nutrient use efficiency, tolerance to abiotic stress, quality traits and availability of nutrients in the soil or rhizosphere. Currently, seaweed extracts account for more than 33% of the total plant biostimulant market. Within this category, Ascophyllum nodosum (AN), is the most widely studied and applied in biostimulant formulations. In contrast, Ecklonia maxima (EM) species, is relatively under researched. In this study the effects of EM seaweed extract (Kelpak®) foliar spray applied: one week before flowering (EL- stage 18), at berry set (EL- stage 27) and at véraison (EL-stage 35) in combination with two different water-status scenarios (non-irrigated and irrigated) were investigated. The four treatments (CIR-, CIR+, EMIR- and EMIR+) were applied in ten min-experimental plots (consisting of 3 vines and 30 vines per treatment) in a commercial block of Vitis vinifera L. cv. Cabernet Sauvignon in the Stellenbosch wine region. The effects on grapevine physiology (gaseous exchange, photosynthesis rate, chlorophyll fluorescence, predawn and stem water potentials), vegetative characteristics, reproductive characteristics (yield components) and the subsequent grape berry and wine metabolites were studied during the 2021-2022 harvest season. Differences in oenological parameters (classical parameters and phenolic composition) were also investigated and compared. Regardless of water status scenario, EM application did not affect vine photosynthetic capacity. Leaf area was positively influenced by the EM foliar applications which resulted in improved sugars and organic acid concentration. Furthermore, the concentration of grape phenolics at harvest were positively influenced which was also evident in the bottled wines from grapes derived from EM treated grapevines. Overall, the data suggest that the use of EM based foliar products, could be beneficial in increasing grape metabolites during the ripening period and could be beneficial for sustainable viticulture.