Antifungal activity of Ecklonia sp. and Jania sp. polysaccharides against Botrytis cinerea

Seaweeds are a source of macro and microelements, amino acids, vitamins, polysaccharides and hormones, such as auxins, auxin-like compounds and cytokinins (Craigie, 2011). Seaweeds extracts (SE) have long been used in agriculture as soil amendment for their beneficial properties on plants, because they stimulate both plant growth and production (Crouch & van Staden, 1992; Arthur et. al., 2003). They also increase fruit weight, fresh dry mass of root, leaf area, yield per plant, the chlorophyll content and minerals (Sivasankari et al., 2006; Rayorath et al., 2008; Roussos et al., 2009). It has also been shown that SE may help the plants to counteract abiotic and biotic stresses. Among abiotic stresses, Ashraf & Foolad (2007) demonstrated that SE are involved in overcoming plant stress conditions such as drought and salinaty. Several studies have shown antibiotic, antiviral and antifungal activities of SE against a number of plant pathogens such as Penicillium spp. and Fusarium oxysporum (Khallil et al., 2015) and Aspergillus sp. (Kosanić et al., 2015). Seaweeds extracts are also rich in several bioactive compounds, such as polysaccharides that are well known to be elicitors of plant defence responses. Simultaneously to the growing consumption of agricultural products, such as strawberry, there was an increase in the use of chemical fertilizers to improve plant yield, and of synthetic pesticides to control fungal plant pathogens. The continuous use of chemicals during the years has affected human and animal health and the ecosystem. Strawberry is one of the most consumed berries and its high nutritional value and composition have stimulated its consumption increase. A number of fungal pathogens can affect strawberry plants such as Colletotrichum spp., and several species of the soil borne pathogens, such as Rhizoctonia, Fusarium and Pythium causing the so-called black root rot complex (Manici et al., 2005). Among these pathogens, Botrytis cinerea, the agent of grey mold, cause several losses especially during shelf life. Alternative approaches to chemical treatments are necessary to preserve the quality of strawberries during the shelf life in order to protect health safety and limit the development of the fungus. In this study, the antifungal activity of cationic polysaccharides extracted from two macroalgae, Ecklonia sp. (Ochrophyta) and Jania sp. (Rhodophyta) was investigated against B. cinerea in vitro and in vivo on strawberry. Polysaccharides were extracted by selective precipitation with 2% (w/v) N-Cetylpyridinium bromide monohydrate (Cetavlon) (Diaz et al., 2011). In the in vitro assay, fungal colony portions were treated for 6 hours by immersion in three polysaccharides aqueous concentrations, 1.65, 0.82 and 0.41 mg/ml for Ecklonia sp. and 0.18, 0.09 and 0.045 mg/ml for Jania sp. The treated colony portions were inoculated in agarized medium and daily growth was measured for a week. Ecklonia sp. polysaccharides at 0.18 mg/ml and 0.09 mg/ml significantly inhibited B. cinerea growth by 21.0% and 22.8%, respectively, two days after treatment. Jania sp. polysaccharides did never inhibit fungal colony growth. For in vivo experiments, strawberry ripe fruits cv. Cristal were immerged before or after harvesting in polysaccharide aqueous solutions of Ecklonia sp. at the concentrations of 0.82 and 0.41 mg/ml, and of Jania sp., at 0.09 and 0.045 mg/ml. A spore suspension of B. cinerea (1 × 105 spores/ml) was inoculated by spraying fruits 24 hours after treatment. Disease symptoms over the total area inoculated of fruit were evaluated as percentage of infected area. The pre-harvest treatment with Jania sp. showed to reduce disease symptoms by 100% at 0.09 mg/ml and by 50% at 0.045 mg/ml and with Ecklonia sp. by 16.7% (0.82 mg/ml) and 11.11% (0.41 mg/ml). Post-harvest treatment did never inhibit disease symptoms. This study showed that SE could be considered for further investigation in control strategy against B. cinerea