Different polyphenolic parenchyma cell and phloem axial resin duct-like structures formation rates in Cupressus sempervirens clones infected with Seiridium cardinale

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.