Seiridium cardinale, the main fungal pathogen responsible for cypress bark canker, is the largest threat to cypresses worldwide. The terpene response of canker-resistant clones of Italian cypress, Cupressus sempervirens, to two differently aggressive isolates of S. cardinale was studied. Phloem terpene concentrations, foliar terpene concentrations, as well as foliar terpene emission rates were analyzed 1, 10, 30, and 90 days after artificial inoculation with fungal isolates. The phloem surrounding the inoculation point exhibited de novo production of four oxygenated monoterpenes and two unidentified terpenes. The concentrations of several constitutive mono-and diterpenes increased strongly (especially α-thujene, sabinene, terpinolene, terpinen-4-ol, oxygenated monoterpenes, manool, and two unidentified diterpenes) as the infection progressed. The proportion of minor terpenes in the infected cypresses increased markedly from the first day after inoculation (from 10 % in the control to 30-50 % in the infected treatments). Foliar concentrations showed no clear trend, but emission rates peaked at day 10 in infected trees, with higher δ-3-carene (15-fold) and total monoterpene (10-fold) emissions than the control. No substantial differences were found among cypresses infected by the two fungal isolates. These results suggest that cypresses activate several direct and indirect chemical defense mechanisms after infection by S. cardinale.
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.
The aim of this study was the characterization of constitutive and induced defence mechanisms in the bark tissues of Cupressus sempervirens before and after infection with the bark fungus Seiridium cardinale that is responsible for Cypress Canker Disease. The time-course development of polyphenolic parenchyma cells (PP cells) and phloem axial resin ducts PARDs(PARD) like structures) in the phloem was investigated in two C. sempervirens clones, one resistant and one susceptible to the disease, through anatomycal and hystologycal observations carried out by light microscope during a 19 days trial. PP cells were constitutively more abundant in the canker resistant clone compared to the susceptible clone, while PARDsPARD-like structures were not present in the bark of untreated plants of both clones. PP cells increased in both clones as a response to infection, but in the resistant clone they were more abundant 5 and 12 days after inoculation. Following inoculation, PARDsPARD-like structures appeared in the phloem after 5 days in the resistant clone and only after 12 days in the susceptible clone. Even the number of secretory cells (surrounding the PARDsPARD-like structures) was higher in the R clone 5 and 12 days after inoculation compared to the S clone. These observations demonstrate a faster phloem response of the resistant clone in the early phase of the infection. This may slow down initial growth of the fungus contributing to the resistance mechanism.
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