<i>Rugulopteryx okamurae</i> extract provides protection against <i>Plasmopara viticola</i>

There is currently a need to assess new, sustainable strategies for downy mildew control on grapevines in accordance with the Goals of the 2030 Agenda for Sustainable Development. Seaweed has proven to be one of the marine resources with the highest potential as plant protective agent, representing an environmentally friendly solution for sustainable wine production. Recently, the biostimulant capacity of Rugulopteryx okamurae, an invasive seaweed, has been demonstrated. The current work evaluates the ability of a R. okamurae extract (RO) to prevent Plasmopara viticola damage on two clones of Tempranillo plants. A greenhouse experiment demonstrated that RO can elicit defense mechanisms and prime grapevines. The response to the seaweed treatment (applied three times at 48-hour intervals) was pronounced at the molecular level, including changes in: i) gene expression (three from PR proteins group and four other genes involved in the flavonoid pathway, lipoxygenase pathway, redox status regulation and cell wall reinforcement), ii) antioxidant enzyme activities (in particular those of superoxide dismutase and gluthatione reductase), and iii) polyphenols, such as total piceid and E-resveratrol. Meanwhile, photosynthetic pigments and photochemical parameters were less affected. The two Tempranillo clones (VN40 and RJ43) exhibited differences in their responses, particularly in their antioxidant enzymes induction, but RJ43 showed stronger elicitation in general. Importantly, plants previously treated with RO, especially RJ43 plants, exhibited a more efficient response to P. viticola infection, with grapevine resistance to the disease being enhanced. Twenty-four hours after pathogen inoculation, RO plants showed a higher induction of antioxidant enzymes (particularly glutathione reductase and ascorbate peroxidase, key to protecting cells from damage), as well as higher viniferins concentrations and an enhancement in the downregulation of various SA-related genes, together with acute upregulation of CHI2 and GST1 expression compared to the biostimulation timepoint. Overall, the results indicate that RO is able to elicit a more efficient response from plants to abiotic stress; the visual inspection of incidence and severity of the disease corroborated the findings that RO treatment significantly reduced both disease incidence and severity in RJ43 by 20 % and 25 %, respectively.