Antifungal Potentials of Ulva fasciata Crude Extracts Against Plant Pathogenic Fungus Pseudopestalotiopsis theae

Abstract

Pseudopestalotiopsis theae is a plant pathogenic fungus responsible for several diseases including grey blight of Camellia sinensis (tea) and leaf yellowing in Solanum melongena (brinjal) in Sri Lanka. The increasing usage of synthetic fungicides to manage such diseases causes a great impact on human and environmental health. Identification of antifungal compounds from natural sources like marine macroalgae is a better alternative. Therefore, the present study was conducted to investigate in vitro antifungal activity of Ulva extracts against P. theae. Ulva samples were collected from Thalpe Beach, Southern Province, Sri Lanka (5.99500 N, 80.28800 E) and its identity was confirmed as Ulva fasciata (OQ427155) using tufA (plastid elongation factor Tu) gene sequence analysis followed by phylogenetic analysis. The crude extracts of the dried algal sample were prepared with four different solvents: hexane, chloroform, ethyl acetate, and methanol using a Soxhlet apparatus. Antifungal potentials of Ulva crude extracts were assessed against molecularly identified fungal pathogen P. theae (MT990526) using the poisoned food technique with 500 ppm and 1000 ppm concentrations. PDA plates with Captan fungicide were used as positive controls while PDA plates without crude extracts were used as negative controls. Five replicates were used for each treatment. Inhibition percentages were calculated after seven days of inoculation. The highest inhibition percentage was shown by Ulva-methanol 1000 ppm treatment (24.21%) followed by Ulva-Ethyl acetate 1000 ppm treatment (16.00%). Further, Ulva-methanol extract was analyzed using Gas Chromatography-Mass Spectroscopy (GC-MS) to determine the potential antifungal compounds. Fourteen different chemical compounds were identified, and their antifungal activity spectra were determined using PASS WAY2DRUG online server. According to probability to be active (Pa) values given by the server Pa=0.591 for 17-octadecenal (CID=41922) and Pa=0.407 for palmitic acid (CID=985), represent the most potential antifungal compounds in the extract. The findings of this study showed that the U. fasciata methanol extract has antifungal properties against P. theae, which makes it a possible source of a natural anti-phytopathogenic agent.