Ammar Nawaim, Aydi Ben Abdallah Rania, Jabnoun-Khiareddine Hayfa, Nefzi Ahlem, Rguez Safa and Daami-Remadi Mejda
Sargassum vulgare aqueous and methanolic extracts were assessed for their capacity to inhibit Fusarium sambucinum and F. solani , the most aggressive and frequent causal agents of potato Fusarium dry rot in Tunisia.The antifungal potential of these extracts varied according to alga sampling sites, extracts (aqueous or methanolic) and concentrations tested. F. sambucinum and F. solani mycelial growth inhibition, recorded after 4 days of incubation at 25°C, was estimated at 30.41 and 39.44%, respectively, using aqueous extract of S. vulgare at 100 mg/mL. F. sambucinum growth was inhibited by more than 32.33% using 100 mg/mL of methanolic extract of alga collected from Tunis. Tested at 50-100 mg/mL, the methanolic extract of alga collected from Tunis had suppressed F. solani growth by up to 46%. Methanolic extracts, applied prior tuber inoculation with F. solani and F. sambucinum, were effective in decreasing disease severity recorded after 21 days of incubation at 25°C. These treatments had lowered the lesion diameter and the rot penetration by 66.65 and 67.51%, respectively, relative to control. The methanolic extract of alga collected from Tunis or Mahdia1 and applied at 50 mg/mL exhibited the highest disease-suppressive ability by decreasing disease severity by 61-63% compared to 3.04-27.13% recorded using carbendazim at the same concentration. Gain of efficiency achieved using S. vulgare methanolic extracts (alga from Mahdia1 and Tunis), compared to reference fungicide (applied at 50 mg/mL), was by up to 47% for lesion diameter and more than 62% for fungicide penetration. The chemical analysis of the methanolic extract of S. vulgare sampled from site of Mahdia1 using HPLC-DAD revealed the presence of phenolic acids and flavonoids. These results suggest that S. vulgare may be explored as potential source of antifungal compounds bioactive against Fusarium spp.