Fusarium inhibition by wild populations of the medicinal plant Salvia africana-lutea L. linked to metabolomic profiling

BACKGROUND: Salvia africana-lutea L., an important medicinal sage used in the Western Cape (South Africa), can be termed a ‘broad-spectrum remedy’ suggesting the presence of a multiplicity of bioactive metabolites. This study aimed at assessing wild S. africana-lutea populations for chemotypic variation and anti-Fusarium properties. METHODS: Samples were collected from four wild growing population sites (Yzerfontein, Silwerstroomstrand, Koeberg and Brackenfell) and one garden growing location in Stellenbosch. Their antifungal activities against Fusarium verticillioides (strains: MRC 826 and MRC 8267) and F. proliferatum (strains: MRC 6908 and MRC 7140) that are aggressive mycotoxigenic phytopathogens were compared using an in vitro microdilution assay. To correlate antifungal activity to chemical profiles, three techniques viz. Gas chromatography-mass spectrometry (GC-MS); Liquid chromatography-mass spectrometry (LC-MS) and (1)H Nuclear Magnetic Resonance (NMR) were employed. Principal Component Analysis (PCA) was applied to the NMR data. The partial least squares-discriminant analysis (PLS-DA) was used to integrate LC-MS and NMR data sets. All statistics were performed with the SIMCA-P + 12.0 software. RESULTS: The dichloromethane:methanol (1:1; v/v) extracts of the plant species collected from Stellenbosch demonstrated the strongest inhibition of F. verticillioides and F. proliferatum with minimum inhibitory concentration (MIC) values of 0.031 mg ml(-1) and 0.063 mg ml(-1) respectively. GC-MS showed four compounds which were unique to the Stellenbosch extracts. By integrating LC-MS and (1)H NMR analyses, large chemotype differences leading to samples grouping by site when a multivariate analysis was performed, suggested strong plant-environment interactions as factors influencing metabolite composition. Signals distinguishing the Stellenbosch profile were in the aromatic part of the (1)H NMR spectra. CONCLUSIONS: This study shows the potential of chemotypes of Salvia africana-lutea in controlling fungal growth and consequently mycotoxin production. Products for use in the agricultural sector may be developed from such chemotypes.