Fusarium crown rot of wheat is an important disease worldwide. The lack of commercial resistant cultivars and effective fungicides against Fusarium, make controlling the disease very difficult. Biocontrol can be an environmentally friendly method to reduce the progress of various diseases caused by Fusarium species. Piriformospora indica is a root endophytic fungus with a wide range of host plants, which increases their growth and tolerance to biotic and abiotic stresses. In this study, capability of P. indica to protect wheat seedlings against Fusarium pseudograminearum, causing crown rot, was investigated and the role of polyamines (PAs) and nitric oxide (NO) as signal molecules involved in plant defense pathways in induced resistance by this endophytic fungus was evaluated in this pathosystem for the first time. Our results showed that P. indica did not have any antagonistic effect on F. pseudograminearum in vitro but considerably reduced the disease progress on wheat seedlings and detached leaves. Also, P. indica increased plant growth parameters compared to the controls in greenhouse. Application of spermidine (Spd; a polyamine) and sodium nitroprusside (SNP; a NO donor) revealed that PAs and NO had significant effect on basal immunity and P. indica-induced resistance (Pi-IR) via elevation of H2O2 levels, guaiacol peroxidase (GPX) and catalase (CAT) activity, callose deposition, relative water content (RWC) and membrane stability index (MSI) compared to the plants only inoculated with F. pseudograminearum and uninoculated controls. In addition, our data demonstrated that PAs and NO synergistically enhanced basal resistance and Pi-IR against Fusarium crown rot in wheat plants.

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