Antifungal efficacy of methanolic extracts of Plectranthus spp. against Fusarium Pathotypes: A sustainable bioactive approach via In Vitro mycelial suppression

Fusarium species, particularly Fusarium oxysporum and F. brachygibbosum, are major pathogens that significantly impact crop productivity and food security. With increasing concerns over mycotoxin contamination and fungicide resistance, there is a growing need for eco-friendly antifungal alternatives. In this context, the genus Plectranthus (Lamiaceae), known for its ethnomedicinal use and phytochemical richness, offers promising potential. This study investigates the antifungal efficacy of methanolic extracts from various Plectranthus species using the food poisoning assay. Extracts from leaves and stems were tested at concentrations of 0.75 mL, 1 mL, and 3 mL against F. oxysporum and F. brachygibbosum. The results revealed dose-dependent inhibition, with leaf extracts generally outperforming stem extracts in fungal growth suppression. Notably, P. barbatus (stem and leaf), P. caninus (stem and leaf), and P. prostratus (leaf) displayed strong antifungal activity, producing significant zones of inhibition comparable to the fungicide control (fluconazole). F. brachygibbosum exhibited greater sensitivity to the treatments than F. oxysporum, suggesting species-specific susceptibility. The findings affirm that Plectranthus extracts, especially from leaves, harbor potent antifungal compounds likely responsible for the observed mycelial growth inhibition. These results underscore the potential of Plectranthus spp. as a sustainable and natural antifungal source. Further research is necessary to isolate the active constituents and validate their efficacy in field conditions. This study contributes to the growing body of evidence supporting plant-based biocontrol strategies as viable alternatives to synthetic fungicides in integrated plant disease management.