Inhibition of plant pathogenic fungi by endophytic Trichoderma spp. through mycoparasitism and volatile organic compounds.

Antagonism of plant pathogenic fungi by endophytic fungi is a well-known phenomenon. In plate assays, the antagonism could be due to mycoparasitism, competition for space or antibiosis, involving a chemical diffusate, or a volatile organic compound (VOC). In this study, we demonstrate that besides mycoparasitism, VOCs play a major role in antagonism of pathogenic fungi by four endophytic fungi belonging to the genus Trichoderma. Using a double-plate assay, we show that all the four endophytic Trichoderma species significantly inhibited mycelial growth of three of the four pathogens, (Sclerotinia sclerotiorum-TSS, Sclerotium rolfsii-CSR and Fusarium oxysporum-CFO), while that of Macrophomina phaseolina-CMP was not affected. GC-MS analysis of the pure cultures of one of the endophytic fungi studied, namely, Trichoderma longibrachiatum strain 2 (Acc. No. MK751758) and the pathogens, F. oxysporum-CFO and M. phaseolina-CMP revealed the presence of several VOCs including hydrocarbons, alcohols, ketones, aldehydes, esters, acids, ethers and different classes of terpenes. In mixed double plates, where the endophyte was grown along with either of the two plant pathogens, F. oxysporum-CFO or M. phaseolina-CMP, there was an induction of a number of new VOCs that were not detected in the pure cultures of either the endophyte or the pathogens. Several of these new VOCs are reported to possess antifungal and cytotoxic activity. We discuss these results and highlight the importance of such interactions in endophyte-pathogen interactions.

Restoration of camptothecine production in attenuated endophytic fungus on re-inoculation into host plant and treatment with DNA methyltransferase inhibitor.

Fungal endophytes inhabit living tissues of plants without any apparent symptoms and in many cases are known to produce secondary metabolites similar to those produced by their respective host plants. However on sub-culture, the endophytic fungi gradually attenuate their ability to produce the metabolites. Attenuation has been a major constraint in realizing the potential of endophytic fungi as an alternative source of plant secondary metabolites. In this study, we report attempts to restore camptothecine (CPT) production in attenuated endophytic fungi isolated from CPT producing plants, Nothapodytes nimmoniana and Miquelia dentata when they are passed through their host plant or plants that produce CPT and when treated with a DNA methyl transferase inhibitor. Attenuated endophytic fungi that traversed through their host tissue or plants capable of synthesizing CPT, produced significantly higher CPT compared to the attenuated fungi. Attenuated fungus cultured in the presence of 5-azacytidine, a DNA methyltransferase inhibitor, had an enhanced CPT content compared to untreated attenuated fungus. These results indicate that the attenuation of CPT production in endophytic fungi could in principle be reversed by eliciting some signals from plant tissue, most likely that which prevents the methylation or silencing of the genes responsible for CPT biosynthesis.