Biological effect of VOCs produced during Pseudomonas syringae pv. actinidiae infection of kiwifruit plant

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 may have an effect on plant signal transduction pathways, thus contributing to pathogenicity or plant defence responses. Strains of the virulent biovar 3 of Pseudomonas syringae pv. actinidiae emit ethylene, both from axenic cultures in a growth medium obtained from Actinidia deliciosa leaf extract, and from infected plants. Accordingly, the infection stimulates the ethylene signal cascade in the host. Other compounds, either emitted by the bacterium (such as 1-undecene, linear ketones and benzyl alcohol), or strongly induced in plants after infection, such as decane, may present a biological activity. Healthy plants react to VOCs from infected neighbours, by activating the phenylpropanoid pathway and several PR genes. However, after the infection, P. syringae pv. actinidiae is able to selectively depress the induced plant defences, possibly by stimulating the oxylipin pathway. Ethylene and oxylipin derivatives, such as jasmonates, may counteract salicylic acid-mediated defences, thus allowing bacterial growth in the host plant. Our research demonstrates that VOCs from infected plants may promote both plant defences and disease development. The further characterization of the signalling pathways involved in such mechanisms may result useful to design plant protection strategies.