CSIRO PUBLISHING www.publish.csiro.au/journals/app Australasian Plant Pathology, 2006, 35, 411–418 Endophytic Chaetomium globosum reduces development of tan spot in wheat caused by Pyrenophora tritici-repentis N. Istifadah A,B and P. A. McGee B,C A Department of Plant Pests and Diseases, Agriculture Faculty, Padjadjaran University, Jatinangor, Bandung 4600, Indonesia. B School of Biological Sciences A12, University of Sydney, NSW 2006, Australia. C Corresponding author. Email: peterm@bio.usyd.edu.au Abstract. Endophytic Chaetomium reduced the development of disease caused by Pyrenophora tritici-repentis in wheat leaves. Chaetomium globosum isolate NC-1 and its culture filtrate, applied to leaves 3, 7 and 14 days before inoculation with the pathogen, reduced the development of tan spot in treated leaves of the susceptible cv. Morocco. The disease reduction differed between host cultivars. Disease reduction was more pronounced in cv. Leichhardt than cv. Morocco. Inoculation of the endophyte or its culture filtrate led to accumulation of extracellular proteins in host tissues indicating activation of host defences. The intercellular washing fluid of endophyte-inoculated leaves lacked an inhibitory effect on the pathogen in vitro, and the inhibitory proteinaceous compound produced by the endophyte in vitro was not detected in the intercellular washing fluid of endophyte-infected leaves. The antagonistic effect of the endophyte against the pathogen in planta was probably due to activation of host defences rather than direct antagonism. Additional keywords: disease reduction, endophytes, host defences, induced resistance, intercellular washing fluids. Introduction Pathogenic and endophytic fungi (Petrini 1991; Wennstrom 1994; Wilson 1995) may co-occur in plants, leading to an interaction between them. The response of the fungi to the plant and the plant response to their individual and combined presence may also influence the interaction between the microorganisms. Competition for infection site and the production of inhibitory compounds may contribute to direct antagonism by the endophyte against other microorganisms, including pathogens, living in the same tissue (Clay 1991; Saikkonen et al. 1998; Wilson 2000). Antagonism between endophyte and pathogen in planta has been inferred. The presence of Neotyphodium coenophialum was associated with reduced Rhizoctonia blight in tall fescue (Burpee and Bouton 1993), and root endophytes with reduced incidence of club root in Chinese cabbage (Narisawa et al. 1998), Verticillium wilt disease in eggplants (Narisawa et al. 2002), Verticillium yellows in Chinese cabbage (Narisawa et al. 2004) and powdery mildew in barley (Vilich et al. 1998). The presence of endophytes within leaf tissues was associated with disease reduction in cacao caused by Phytophthora sp. (Arnold et al. 2003) and rust disease in wheat (Dingle and McGee 2003). The presence of endophytes may alter disease development or specific pathogen activity in the plant, and disease development may be used to indicate an interaction. When endophyte colonisation is intercellular, the interaction between endophyte and pathogen may take place in the host apoplast. If inhibitory metabolites of the endophyte directly antagonise the pathogen, the inhibitors are likely to be detected in the apoplast. An interaction between endophyte and pathogen need not be apparent. The presence of an endophyte did not alter pathogenicity or sporulation of Drechslera dictyoides in ryegrass (Cromey and Cole 1984), N. (Acremonium) coenophialum did not influence infection of tall fescue by Puccinia graminis subsp. graminicola (Welty et al. 1991) and Neotyphodium sp. did not influence the severity of basal tiller rot in tall fescue and perennial ryegrass (Hume et al. 1997). These observations indicate that potentially complex mechanisms underlie the interaction between endophyte and pathogen in a host. Antagonistic interactions between endophytes and plant pathogens in plants may be directly and/or indirectly mediated by the host. The presence of endophytes in the host plant may stimulate defence reactions, expressed as physiological (Peters et al. 1998) and morphological alterations in the host tissues (Cabral et al. 1993), leading to © Australasian Plant Pathology Society 2006 10.1071/AP06038 0815-3191/06/040411