ANTIFUNGAL EFFICACY OF GRACILARIA EDULIS EXTRACTS AGAINST FUSARIUM PATHOGENS OF SUGARCANE

Abstract

Sugarcane production is adversely affected by fungal diseases, highlighting the need for effective and environmentally compatible disease-management strategies. The present study investigated the in vitro antifungal activity of the red seaweed Gracilaria edulis against Fusarium isolates obtained from diseased sugarcane collected from three districts of Tamil Nadu, India. Diseased stalk tissues from Ramanathapuram, Namakkal, and Karur were cultured on Potato Dextrose Agar (PDA), and the resulting fungal isolates were characterized based on cultural and microscopic features using lactophenol cotton blue staining. The isolates were morphologically identified as Fusarium verticillioides from Ramanathapuram and Fusarium sacchari from Namakkal and Karur. G. edulis collected from Pudumadam was washed, shade-dried, powdered, and extracted using distilled water and acetone. Qualitative phytochemical screening revealed the presence of flavonoids, saponins, alkaloids, carbohydrates, and proteins in the aqueous extract, whereas the acetone extract contained flavonoids, carbohydrates, alkaloids, and phytosterols. The antifungal activity of the acetone extract was evaluated using the agar well diffusion assay at 10, 20, and 50 µL. The extract exhibited inhibitory activity against all tested isolates, with inhibition generally increasing with extract volume. The maximum inhibition zone of 20 mm was recorded against the Ramanathapuram-associated F. verticillioides isolate at 50 µL, followed by 15 mm and 10 mm against the Karur- and Namakkal-associated F. sacchari isolates, respectively. These findings provide preliminary in vitro evidence for the antifungal potential of G. edulis extract against sugarcane-associated Fusarium fungi. However, the fungal isolates were identified solely on the basis of phenotypic characteristics, and the antifungal assessment was restricted to an in vitro assay. Molecular confirmation of pathogen identity, quantitative determination of antifungal potency, chemical characterization of active constituents, replicated dose-response studies, mechanistic investigations, and greenhouse and field evaluations are necessary to establish the efficacy, safety, and practical potential of G. edulis-derived antifungal agents for sustainable sugarcane disease management.