Evaluation of an alternative mean for controlling postharvest Rhizopus rot of strawberries

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.