Abstract
The canker-causing fungus Seiridium cardinale is the major threat to Cupressus sempervirens worldwide. We investigated the production of terpenes by canker-resistant and susceptible cypresses inoculated with S. cardinale, the effect of these terpenes on fungal growth, and the defensive biotransformation of the terpenes conducted by the fungus. All infected trees produced de novo terpenes and strongly induced terpenic responses, but the responses were stronger in the canker-resistant than the susceptible trees. In vitro tests for the inhibition of fungal growth indicated that the terpene concentrations of resistant trees were more inhibitory than those of susceptible trees. The highly induced and de novo terpenes exhibited substantial inhibition (more than a fungicide reference) and had a high concentration-dependent inhibition, whereas the most abundant terpenes had a low concentration-dependent inhibition. S. cardinale biotransformed three terpenes and was capable of detoxifying them even outside the fungal mycelium, in its immediate surrounding environment. Our results thus indicated that terpenes were key defences efficiently used by C. sempervirens, but also that S. cardinale is ready for the battle.
Highlights
Terpenes, among the main defences of conifers, act as a first line of defence against biological agents and are usually strongly induced when trees are infected by bark-beetle/fungal pathogen complexes[1,2]
Camphor, and oxygenated MT1 and 2, were de novo terpenes exclusively found in the infected states of both groups
The terpenes found in Italian cypress tissues in response to S. cardinale infection may be produced by the tree, as endophytic microorganisms could be contributing to cypress defence[31]
Summary
Among the main defences of conifers, act as a first line of defence against biological agents and are usually strongly induced when trees are infected by bark-beetle/fungal pathogen complexes[1,2]. The inhibition caused by arbitrary concentrations of terpenes (especially monoterpenes (MTs)) has been tested on conifer pathogens, but experiments studying the effects of in planta concentrations are rare[10,11]. The biotransformation of terpenoids has been studied in only a few fungal pathogens of Pinaceae[12,17], Grosmannia clavigera in particular[15,18], so our understanding of fungal resistance to terpenes remains very poor, despite it is crucial to understand any conifer pathosystem. The phloem of infected canker-resistant trees produce de novo MTs www.nature.com/scientificreports/
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