Abstract
Crude extract of the brown seaweed Laminaria digitata was tested as an alternative mean to control postharvest Rhizopus rot of strawberries. The antifungal activity of four extracts (one un-fractionated and three soluble by hexane, ethanol, and water) was in vitro measured against one pathogenic isolate of Rhizopus stolonifer at a concentration range from 10 g L-1 to 30 g L-1. The antifungal activity of the un-fractionated extract was in vivo measured into a climatic room at the same concentration range in comparison to fungicide Fenhexamid in preventive and curative treatments. The peroxidase activity in L. digitata-treated inoculated strawberries was performed. A significant inhibition of mycelia growth applying 30 g L-1 of un-fractionated extract (until 80% after 5 days) and suppression of sporangia germination (until 95% after 24 hours) were found by a dose-dependent manner of the treatment. Only the extracts fractionated by hexane and ethanol were likewise suppressive at the same concentrations against mycelia (until 71% and 66% respectively) and sporangia (until 82% and 69% respectively) such involving a direct toxicity induced by lipids and phenolic compounds to R. stolonifer suppression. Fruit decay inhibition of the R. stolonifer/strawberries pathosystem increased from 10 g L-1 to 30 g L-1 until 75% after 4 days only in preventive treatment. An increased peroxidase activity (4.84 ΔOD420 g-1 min-1) seen in fruit tissue after one-day from the application of 30 g -1 raw extract suggests that in vivo suppression could also be related to induced systemic resistance phenomena.
