Characterization of Antifungal Natural Products Isolated from Endophytic Fungi of Finger Millet (Eleusine coracana)

Abstract

Abstract:Finger millet is an ancient African-Indian crop that is resistant to many pathogens including the fungus, Fusarium graminearum. We previously reported the first isolation of putative fungal endophytes from finger millet and showed that the crude extracts of four strains had anti-Fusarium activity. However, active compounds were isolated from only one strain. The objectives of this study were to confirm the endophytic lifestyle of the three remaining anti-Fusarium isolates, to identify the major underlying antifungal compounds, and to initially characterize the mode(s) of action of each compound. Results of confocal microscopy and a plant disease assay were consistent with the three fungal strains behaving as endophytes. Using bio-assay guided fractionation and spectroscopic structural elucidation, three anti-Fusarium secondary metabolites were purified and characterized. These molecules were not previously reported to derive from fungi nor have antifungal activity. The purified antifungal compounds were: 5-hydroxy 2(3H)-benzofuranone, dehydrocostus lactone (guaianolide sesquiterpene lactone), and harpagoside (an iridoide glycoside). Light microscopy and vitality staining were used to visualize the in vitro interactions between each compound and Fusarium; the results suggested a mixed fungicidal/fungistatic mode of action. We conclude that finger millet possesses fungal endophytes that can synthesize anti-fungal compounds not previously reported as bio-fungicides against F. graminearum.

Fungal Root Microbiome from Healthy and Brittle Leaf Diseased Date Palm Trees (Phoenix dactylifera L.) Reveals a Hidden Untapped Arsenal of Antibacterial and Broad Spectrum Antifungal Secondary Metabolites

“…Endophytes especially fungi produce an impressive myriad of bioactive molecules and enzymes that cope with pathogen infection of plants ( Newman and Cragg, 2016 ; Vasundhara et al, 2016 ). Natural compounds produced by endophytic fungi have been shown to interfere with key host and pathogen processes required for successful infection of the host and to mitigate the adverse effects of broad variety of animal and plant pathogens ( Stierle and Stierle, 2015 ; Mousa et al, 2016 ; Tanney et al, 2016 ). Endophytic fungi have tremendous impacts on their host plants inducing their tolerance to biotic and abiotic stresses, promoting their growth and the production of wide variety of secondary metabolites ( Jia et al, 2016 ).…”

Host–Multi-Pathogen Warfare: Pathogen Interactions in Co-infected Plants

“…A classic example of chemical aggression includes tenuazonic acid secreted by the finger millet colonizing endophyte Phoma sp. which prevents growth of several pathogens including the toxigenic fungus F. graminearum ( Mousa et al, 2015 , 2016a ). Mechanical aggression also occurs through disruption of cell membranes and formation of multilayer physical barriers limiting growth and infection success of competitors.…”

Endophytic Fungi: A Source of Potential Antifungal Compounds

“…Compounds 128 – 130 exhibited antifungal activity against F. graminearum with the MIC of 31.25, 250.00 and 31.25 µg/mL, respectively. An in vitro interaction between each compound and Fusarium was investigated using light microscopy and vitality staining where the results proposed a mixed fungicidal/fungistatic mode of action [ 70 ].…”