Antifungal Efficacy of Kappaphycus alvarezii and Other Macro-algae against Alternaria solani Induced Early Blight in Tomato (Solanum lycopersicum L.)

Aims: To evaluate the antifungal activity of various seaweed extracts against A. solani under in vitro conditions. Methodology: The pathogen A.solani was isolated and its pathogenicity confirmed through inoculation on tomato plants. Molecular characterization was performed using PCR amplification and sequencing of the Internal Transcribed Spacer (ITS) region. Seaweed species, including Sargassum wightii, Kappaphycus alvarezii, Gracilaria edulis, Caulerpa racemosa, and Ulva lactuca, were collected, processed, and extracted using various solvents. The antifungal activity of these seaweed extracts was assessed using the Poisoned Food Technique, measuring the inhibition of A. solani growth. Results: Among the seaweed extracts tested, Kappaphycus alvarezii demonstrated the highest antifungal activity, with a maximum mycelial growth inhibition of 76% at a 5% concentration. Sargassum wightii also showed significant antifungal properties, with a 71.10% reduction in mycelial growth. Conclusion: The study reveals the promising potential of seaweed extracts, particularly Kappaphycus alvarezii and Sargassum wightii, as natural antifungal agents against A. solani. These findings suggest that seaweed-based bio-stimulants could serve as effective, eco-friendly alternatives to chemical fungicides in managing early blight disease in tomatoes are in tomato crops and highlights the potential of seaweed extracts as a natural antifungal agent.