An endophytic fungus isolated from finger millet (Eleusine coracana) produces anti-fungal natural products

Abstract

Finger millet is an ancient African cereal crop, domesticated 7000 years ago in Ethiopia, reaching India at 3000 BC. Finger millet is reported to be resistant to various fungal pathogens including Fusarium sp. We hypothesized that finger millet may host beneficial endophytes (plant-colonizing microbes) that contribute to the antifungal activity. Here we report the first isolation of endophyte(s) from finger millet. Five distinct fungal species were isolated from roots and predicted taxonomically based on 18S rDNA sequencing. Extracts from three putative endophytes inhibited growth of F. graminearum and three other pathogenic Fusarium species. The most potent anti-Fusarium strain (WF4, predicted to be a Phoma sp.) was confirmed to behave as an endophyte using pathogenicity and confocal microscopy experiments. Bioassay-guided fractionation of the WF4 extract identified four anti-fungal compounds, viridicatol, tenuazonic acid, alternariol, and alternariol monomethyl ether. All the purified compounds caused dramatic breakage of F. graminearum hyphae in vitro. These compounds have not previously been reported to have anti-Fusarium activity. None of the compounds, except for tenuazonic acid, have previously been reported to be produced by Phoma. We conclude that the ancient, disease-tolerant crop, finger millet, is a novel source of endophytic anti-fungal natural products. This paper suggests the value of the crops grown by subsistence farmers as sources of endophytes and their natural products. Application of these natural chemicals to solve real world problems will require further validation.

Root-hair endophyte stacking in finger millet creates a physicochemical barrier to trap the fungal pathogen Fusarium graminearum

“…Field testing will determine the efficacy of M6 under real-world conditions that include soil-derived microbial competitors. Further studies are needed to determine whether the anti-F. graminearum fungal endophytes of millet 4 cooperate with M6 in RHESt or act at other susceptible locations, and how M6 functions in heterologous hosts and tissues. For example, our group has shown different endophytes within a community interact with one another to stimulate biosynthesis of a fungicide 48 .…”

“…Root-hair endophyte stacking in finger millet creates a physicochemical barrier to trap the fungal pathogen Fusarium graminearum Walaa K. Mousa 1,2 , Charles Shearer 1 , Victor Limay-Rios 3 , Cassie L. Ettinger 4 , Jonathan A. Eisen 4 and Manish N. Raizada 1 *…”

“…3). Subsistence farmers report that finger millet is widely resistant to pathogens including Fusarium species 4,5 . One species, F. graminearum, causes devastating diseases in crops related to finger millet, including maize and wheat, associated with accumulation of the mycotoxin deoxynivalenol (DON), which affects humans and livestock 6,7 .…”

“…One species, F. graminearum, causes devastating diseases in crops related to finger millet, including maize and wheat, associated with accumulation of the mycotoxin deoxynivalenol (DON), which affects humans and livestock 6,7 . Despite its prevalence across cereals, curiously, F. graminearum is not an important pathogen of finger millet 4,8 .…”

“…These observations suggest the possibility of co-evolution within finger millet of Fusarium and millet endophytes. We previously isolated fungal endophytes from finger millet and showed that their natural products have anti-Fusarium activity 4 . We could not find reports of bacterial endophytes isolated from finger millet.…”