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.
