In vitro evaluation of salt-based antifungal compounds for sustainable control of Neoscytalidium dimidiatum

Objective: This study evaluated the antifungal potential of various salts—specifically ammonium, borate, calcium, magnesium, potassium, and sodium compounds—against two isolates (Ol_Dr04 and Ciar 64) of Neoscytalidium dimidiatum under in vitro conditions. The goal was to assess the efficacy of these salts in inhibiting mycelial growth, arthrospore germination, and germ tube elongation under both fixed and adjusted pH conditions. Materials and Methods: In this study, the mycelial growth of N. dimidiatum isolates was first observed across a pH range of 2 to 12 to determine the optimal pH levels. Subsequently, the antifungal efficacy of 1% concentrations of ammonium, borate, calcium, magnesium, potassium, and sodium salts was assessed under both fixed and adjusted pH (5) conditions for both isolates. Effective salt concentrations (EC50) needed to achieve a 50% reduction in mycelial growth, arthrospore germination, and germ tube elongation were calculated using probit analysis. Additionally, minimum inhibitory concentration (MIC) and minimum fungicidal concentration (MFC) values were determined for each salt under the tested conditions. Results: Under fixed pH conditions, 1% concentrations of ammonium (bicarbonate and carbonate), borate (anhydrous borax, Etidot-67, and hydrated borax), and sodium (benzoate, citrate tetrahydrate, and metabisulfite) salts completely inhibited mycelial growth in both fungal isolates. However, under adjusted pH (5) conditions, only sodium benzoate and metabisulfite maintained the same inhibitory effect. At adjusted pH, calcium oxide and propionate also fully suppressed mycelial growth. Sodium metabisulfite emerged as the most effective antifungal compound, with remarkably low EC50 values (0.016 and 0.017%; w/v), MIC (0.0625 and 0.0625%; w/v), and MFC (0.0625% and 0.0625%; w/v) concentrations. Furthermore, with EC50 below 0.03125%, sodium metabisulfite remained the strongest inhibitor in both arthrospore germination and germ tube elongation assays. Conclusion: These results highlight the potential of sodium metabisulfite, ammonium bicarbonate, and ammonium carbonate salts as environmentally friendly alternatives to conventional fungicides. Further in vivo studies are recommended to validate these findings and explore practical applications in sustainable plant disease management.