Postharvest Control of Strawberry Fruit Soft Rot by Laminaria Digitata Extracts

The aim of this work was to assess the potential suppression of extracts of Laminaria digitata for controlling postharvest soft rot of strawberries by Rhizopus stolonifer. The antifungal activity of raw extract and fractionated by hexane, ethanol and water was in vitro measured at a concentration range. The activity of the raw extract was in vivo assessed at the same concentration range in comparison to fungicide Fenhexamid. Observations by scanning electron microscopy of R. stolonifer were performed. The peroxidase activity in L. digitata-treated inoculated strawberries was assessed. A significant inhibition of mycelia growth (until 80% after 5 days of incubation) and suppression of sporangia germination (up to 95% after 24 hours) were found applying 30 g L-1 raw extract. Only extracts fractionated by hexane and ethanol were suppressive against mycelia (until 71% and 67% respectively) and sporangia (up to 82% and 69% respectively). Fruit decay inhibition on the R. stolonifer/strawberries pathosystem increased up to 75% after 3 days of incubation in preventive treatment after application of increasing doses of the extracts. Efficacy of the treatments was related to dose of extract in all the trials. The increased peroxidase activity (up to 7.04 ΔOD420 g−1 min−1) observed in fruit tissue after one- day from application of 30 g L-1 raw extract suggests that suppression could also be due to activation of systemic acquired resistance in artificially infected strawberry fruit.