Extract from the Macroalgae Ulva rigida Induces Table Grapes Resistance to Botrytis cinerea

Fungal pathogens are a central cause of the high wastage rates of harvested fruit and vegetables. Seaweeds from the genus Ulva are fast-growing edible green macroalgae whose species can be found on the shore of every continent, and therefore present a resource that can be utilized on a global scale. In this study, we found that the application of ulvan extract, a sulfated polysaccharide extracted from Ulva rigida (1000 mg/L), elicited table grapes defense and reduced the incidence and decay area of Botrytis cinerea by 43% and 41%, respectively. In addition, compared to the control group at two days post-treatment, ulvan extract elicited a variety of defense-related biomarkers such as a 43% increase in the activity of reactive oxygen species, 4-fold increase in the activity of catalase, 2-fold increase in the activity of superoxide dismutase and 1.4-fold increase in the activity of chitinase. No increase was observed in phenylalanine ammonia-lyase activity, and the treatment did not affect fruit quality parameters such as the pH levels, sugar levels, and titratable acidity of grapes. These results illustrate the potential of ulvan extract to naturally induce the plant defense response and to reduce postharvest decay.