Pythium leak control in potato using aqueous and organic extracts from the brown alga Sargassum vulgare (C. Agardh, 1820)

The antifungal activity of the brown macroalga, Sargassum vulgare (C. Agardh, 1820), collected from different sites along Tunisian costs, was assessed against Pythium aphanidermatum causing Pythium leak disease in potato. Aqueous and organic extracts of this alga, used at different concentrations, were screened in vitro using the poisoned food technique and in vivo on potato tubers cv. Spunta for their ability to inhibit P. aphanidermatum mycelial growth and to suppress potato leak severity. All extracts tested showed antifungal activity toward the targeted pathogen depending on sampling sites, concentrations tested and organic solvent used for extraction. For aqueous extracts, the highest inhibition of pathogen radial growth, by 28%, was achieved using extracts from Tunis and Mahdia1 sites tested respectively at 40 and 50 g L−1. Pythium leak severity was reduced by 34.33 and 31.67% using S. vulgare extracts from Tunis and Monastir, respectively, with these treatments being the most effective. Among S. vulgare organic extracts tested, the methanolic extract displayed the strongest antifungal potential either by inhibiting pathogen mycelial growth by almost 51%, or by reducing disease severity noted on potato tubers cv. Spunta by more than 82% over untreated controls. A total of 34 compounds were identified and quantified using HPLC-DAD chemical profiling in methanolic crude extracts of S. vulgare samples removed from Tunis and Monastir. Presence of phenolic acids and flavonoids may explain the strong antifungal activity displayed by S. vulgare against P. aphanidermatum. These results suggest that S. vulgare may be explored for the isolation of antifungal compounds for Pythium leak control.