Characterization of volatile organic compounds emitted by kiwifruit plants infected with Pseudomonas syringae pv. actinidiae and their effects on host defences

A wide range of volatile organic compounds (VOCs) is released during plant–pathogen interactions both by the pathogens and the hosts. Some of these VOCs are specific for the different diseases and are known to play a role in the pathogenicity or in plant defence responses. Besides, disease-specific VOCs may serve as markers for diagnostic protocols, which allow a non-destructive and rapid screening of bulk samples of plant material. This work aimed to verify the feasibility of a VOC-based diagnosis and to investigate the possible biological role of VOCs released during the plant–pathogen interactions. The volatile emissions from Pseudomonas syringae pv. actinidiae in axenic cultures and from inoculated in vitro kiwifruit plants were characterized by gas chromatography–mass spectrometry (GC–MS) and proton transfer reaction–time-of-flight-mass spectrometry (PTR–ToF-MS). By GC–MS, several putative biochemical markers, such as 1-undecene, were identified. PTR–ToF-MS resulted highly effective in screening the plant material for latent infections. To develop a more user-friendly, portable and less expensive diagnosis system, two different electronic nose models were tested for the early diagnosis of P. syringae pv. actinidiae in asymptomatic plant material. Our experiments demonstrated the feasibility of the electronic nose-based screening of infected plant material. Concerning the biological role of the VOCs released during the plant–pathogen interactions, the exposure of healthy plants to VOCs from infected ones influences the plant growth and induces the stimulation of protective responses. However, after the infection, P. syringae pv. actinidiae is able to selectively inactivate the induced plant defences.