Antifungal Fatty Acids Produced by Coniochaeta ligniaria: A Cryptic Endophytic Fungus Associated with Smallanthus sonchifolius' Autotrophic Cultures
Few studies have addressed the presence and bioactivity of endophytic fungi living in plantlets growing under in vitro conditions. The objectives of the study were: 1) to identify a fungus UM 109 growing as endophytes of autotrophic cultures of the medicinal plant Smallanthus sonchifolius (yacon), and 2) to isolate the compounds produced by this endophyte that showed antifungal properties. The species was identified as Coniochaeta ligniaria using molecular and morphological methods. The crude extract of C. ligniaria displayed antifungal activity. The identification of the active constituents was done by systematic bioactivity-guided fractionation of the dichloromethane extract against the phytopathogenic Colletotrichum species, NMR spectroscopy and GC-FID analysis. The antifungal fractions from the C. ligniaria were identified as a mixture of 12 antifungal fatty acids, including caproic, caprylic, myristic, palmitic, heptadecanoic, stearic, oleic, linoleic and stearic. The presence of antifungal fatty acids was not unique to the fractions of C. ligniaria culture and caproic, caprylic, myristic, palmitic, heptadecanoic, stearic, oleic and linoleic acids were isolated and detected in the antifungal fractions of S. sonchifolius. In conclusion, the identification of the fungus C. ligniaria isolated from in vitro S. sonchifolius plantlets suggest that autotrophic cultures can shelter specific endophytic fungal communities in a special symbiosis with their plant hosts. Furthermore, the detection of the antifungal fatty acids produced by C. ligniaria in the plant fractions suggests that fungus and host together produced compounds that may help S. sonchifolius to resist to phytopathogenic fungal attacks. Acknowledgements: This work received partial support of the Conselho Nacional de Desenvolvimento Científico e Tecnológico (processo 200774/2011 – 5). The authors thank Ms. J.L. Robertson, Ms. R. Pace, Ms. Amber Reichley and Mr. Solomon Green III for technical support.