In vitro and in vivo evaluation of phytoextracts for the management of citrus scab caused by Elsinoe fawcettii

Abstract

Citrus scab is a major fungal disease limiting citrus production, necessitating environmentally safe alternatives to synthetic fungicides. This study evaluated the efficacy of selected phytoextracts under in vitro and in vivo conditions. In vitro assays demonstrated that all extracts significantly inhibited fungal growth, with neem showing the highest and most consistent inhibition across concentrations and time intervals. At S/2, neem achieved up to 62.04% inhibition at 5 days, increasing to 70.70% at 9 days, followed by eucalyptus and garlic, while cinnamon, turmeric, ginger, and thyme showed moderate to weak activity. Tea tree, oregano, and aloe vera were least effective. In vivo evaluation revealed that neem substantially reduced disease severity across all tested citrus cultivars, lowering infection levels to approximately 5-10%, thereby classifying most responses as resistant. Garlic and eucalyptus provided moderate disease suppression, resulting in resistant to tolerant responses depending on cultivar and concentration. Multivariate analyses (cluster analysis and PCA) confirmed strong genotype-dependent responses and consistently identified neem treatments as the most stable and effective across cultivars, while eucalyptus showed greater variability and garlic intermediate performance. FTIR characterization of neem, eucalyptus, and garlic extracts confirmed the presence of phenolics, flavonoids, terpenoids, and sulfur-containing compounds, supporting their antifungal potential. In conclusion, neem extract exhibited superior and broad-spectrum antifungal efficacy against citrus scab, with strong potential for development as a sustainable plant-based disease management strategy.