Coniochaeta ligniaria: antifungal activity of the cryptic endophytic fungus associated with autotrophic tissue cultures of the medicinal plant Smallanthus sonchifolius (Asteraceae)

Abstract

Few studies have addressed the presence and bioactivity of endophytic fungi living in plantlets growing under in vitro conditions. After unfruitful attempts to grow axenic shoot cultures of the medicinal plant Smallanthus sonchifolius (yacon) were made, healthy shoots grew on half strength Murashigue and Skoog media supplemented with 2.2 μM benzylaminopurine without sucrose. We isolated a fungus UM109 from these autotrophic tissue cultures and it was identified as Coniochaeta ligniaria using molecular, physiological and morphological methods. Dichloromethane extracts from C. ligniaria and its host S. sonchifolius exhibited antifungal activity against phytopathogenic fungi Colletotrichum acutatum, C. fragariae and C. gloeosporioides. Both extracts of C. ligniaria and S. sonchifolius were subjected to antifungal bioassay-directed fractionation using NMR spectroscopy and GC-FID analysis. Twelve antifungal fatty acids were identified and 8 out of the total were produced by the fungus and the plant including caproic, caprylic, myristic, palmitic, heptadecanoic, stearic, oleic and linoleic acids. Additionally, caproic, caprylic and palmitic acids were produced at high concentrations by the endophytic fungus and its host. The detection of these antifungal fatty acids produced by both C. ligniaria and S. sonchifolius suggests that these bioactive compounds may be partially responsible for the high resistance of S. sonchifolius to phytopathogenic fungal attacks. This finding also indicates the existence of an interesting chemical symbiosis between an endophytic fungus and its host. Furthermore, the isolation of C. ligniaria from tissue culture of S. sonchifolius demonstrates that plantlets growing in vitro as autotrophic cultures can shelter specific endophytic fungal communities. The use of autotrophic tissue cultures may become an important tool for studies on the taxonomy, ecology, evolution and biotechnological application of endophytes.