ORIGINAL ARTICLE Secondary metabolites produced by a root-inhabiting sterile fungus antagonistic towards pathogenic fungi F. Vinale 1 , E.L. Ghisalberti 2 , G. Flematti 2 , R. Marra 1 , M. Lorito 1 and K. Sivasithamparam 3 1 Dipartimento di Arboricoltura Botanica e Patologia Vegetale, Facolta ` di Agraria, Universita ` degli Studi di Napoli ‘Federico II’ and Istituto CNR per la Protezione delle Piante, sezione di Portici, Naples, Italy 2 School of Biomedical, Biomolecular and Chemical Sciences, Faculty of Life and Physical Sciences, The University of Western Australia, Crawley, WA, Australia 3 School of Plant Biology – Faculty of Natural and Agricultural Sciences, The University of Western Australia, Crawley, WA, Australia Introduction Root-cortex-inhabiting saprophytic fungi are considered to be promising biocontrol agents thanks to their capabil- ity to protect the host vascular system and to interfere chemically with the invading pathogens (Sivasithamparam 1998). Moreover, indirect effects are related to the induc- tion of disease resistance (i.e. lignification of cell walls, production of antifungal compounds) or promotion of plant growth (i.e. proliferation of roots to compensate or mask the effects of the pathogens) (Sivasithamparam 1998). One of these micro-organisms is the sterile red fungus (SRF) isolated from surface-sterilized roots of wheat and ryegrass at seedling and tillering stages in Wes- tern Australia (Dewan and Sivasithamparam 1988). The SRF is an endophyte that provides significant protection to the host in sterilized and nonsterilized soils (Siva- sithamparam 1998). The major characteristics of this basidiomycete are: (i) colonization of the cortical tissues resulting in the formation of a mantle on the root; (ii) high rhizosphere competence; (iii) colonization and sur- vival on live seed (Dewan and Sivasithamparam 1990); (iv) production of antifungal exudates (Gillespie-Sasse et al. 1991); (v) competition for thiamine; (vi) hyphal lysis of the pathogens (Shankar et al. 1994); and (vii) growth promotion effect in planta (i.e. on rotational Keywords antibiosis, 4-(hydroxymethyl)-quinoline, plant growth promotion, secondary metabolites, sterile red fungus, veratryl alcohol. Correspondence Francesco Vinale, Via Universita ` no. 100, 80055 Portici (Naples), Italy. E-mail: frvinale@unina.it 2009 ⁄ 1695: received 24 September 2009, revised and accepted 13 January 2010 doi:10.1111/j.1472-765X.2010.02803.x Abstract Aims: A sterile red fungus (SRF) isolated from cortices of roots of both wheat (Triticum aestivum cv. Gamenya) and ryegrass (Lolium rigidum cv. Wimmera) was found to protect the hosts from phytopathogens and promote plant growth. In this work, the major secondary metabolites produced by this SRF were analysed, and their antibiotic and plant-growth-promoting activities inves- tigated. Methods and Results: Two main compounds, veratryl alcohol (VA) and 4-(hy- droxymethyl)-quinoline, were isolated from the culture filtrate of the fungus. In antifungal assays, VA inhibited the growth of Sclerotinia sclerotiorum and Pythium irregulare even at low amounts, while high concentrations (>100 lg per plug) of 4-(hydroxymethyl)-quinoline were needed. Both metabolites revealed weak inhibition of Rhizoctonia solani. Furthermore, both compounds showed a growth promotion activity on canola (Brassica napus) seedlings used as bioassays. Conclusions: Isolation and characterization of the main secondary metabolites from culture filtrates of a root-inhabiting sterile fungus are reported. The biological assays indicate that these secondary metabolites may have a role in both plant growth regulation and antifungal activity. Significance and Impact of the Study: This study provides a better understand- ing of the metabolism of a cortical fungus that may have a useful role in the biological suppression of root-infecting soil-borne plant pathogens. Letters in Applied Microbiology ISSN 0266-8254 380 Journal compilation ª 2010 The Society for Applied Microbiology, Letters in Applied Microbiology 50 (2010) 380–385 ª 2010 The Authors