Volatiles emitted by leaf rust infected wheat induce a defence response in exposed uninfected wheat seedlings

Volatile organic compounds emitted from plant tissues have been implicated to play many roles. Interplant signalling is an experimentally proven phenomenon whereby volatiles produced under stress conditions may diffuse to neighbouring plants to induce a response. The current project was undertaken to investigate a putative signalling event between leaf rust ( Puccinia triticina Erikss.) infected and uninfected wheat ( Triticum aestivum L.) using a continual air-flow system. Exposure to volatiles emitted by either infected resistant or susceptible plants decreased the percentage leaf area infected and pustule size in recipient plants after a subsequent infection with leaf rust, but in the case of infected resistant plants, the decrease in percentage leaf area infected was significant. The activation of a defence response was confirmed through a significant induction of β-1,3-glucanase activity at 8 h post volatile exposure in exposed resistant and susceptible seedlings, depending on the source of the volatiles. Increased PR1 gene expression supported the activation of the defence response. Emitted volatiles were captured by solid phase micro-extraction and identified by GC-MS. Based on their detection and the literature, ocimene from infected resistant seedlings and green leaf volatiles from infected susceptible seedlings are suggested as likely candidates for the inter-plant communication.