Piriformospora indica protects barley from root rot caused by Fusarium graminearum

The beneficial endophytic fungus Piriformospora indica colonizes barley (Hordeum vulgare L.) roots, which results in protection against diseases and abiotic stress and eventually in higher yield. Infection of the roots with pathogenic necrotrophic fungi of the genus Fusarium, in contrast, leads to necrotized roots and severe reduction of root and shoot biomass. Upon infestation with P. indica, roots were protected from Fusarium infections as evidenced by reduced root rot symptoms. Consistently, Fusarium quantification using quantitative polymerase chain reaction (Q-PCR) revealed a correlation between reduced root rot symptoms and the relative amount of fungal DNA. In vitro analysis of the interaction of P. indica and F. graminearum under axenic culture conditions did not reveal reciprocal growth inhibition suggesting that retardation of Fusarium in roots is mediated by a plant response rather than by antibiosis. Expression of pathogenesis-related genes strongly increased in response to F. graminearum infections, but in contrast was diminished in the presence of P. indica, indicating that PR proteins do not play a crucial role in the P. indica-mediated resistance response to Fusarium.