Terpenoid Accumulation Links Plant Health and Flammability in the Cypress-Bark Canker Pathosystem

Abstract: To explore the possible relationship between diseased trees and wildfires, we assessedthe flammability of canker-resistant and susceptible common cypress clones that were artificiallyinfected with Seiridium cardinale compared to healthy trees. This study explored the eect ofterpenoids produced by the host plant in response to infection and the presence of dead plant portionson flammability. Terpenoids were extracted and quantified in foliage and bark samples by gaschromatography-mass spectrometry (GC-MS). A Mass Loss Calorimeter was used to determine themain flammability descriptors. The concentration of terpenoids in bark and leaf samples and theflammability parameters were compared using a generalized linear mixed models (GLMM) model.A partial least square (PLS) model was generated to predict flammability based on the content ofterpenoid, clone response to bark canker and the disease status of the plants. The total terpenoidcontent drastically increased in the bark of both cypress clones after infection, with a greater (7-fold)increase observed in the resistant clone. On the contrary, levels of terpenoids in leaves did notalter after infection. The GLMM model showed that after infection, plants of the susceptible cloneappeared to be much more flammable in comparison to those of resistant clones, showing higherignitability, combustibility, sustainability and consumability. This was mainly due to the presence ofdried crown parts in the susceptible clone. The resistant clone showed a slightly higher ignitabilityafter infection, while the other flammability parameters did not change. The PLS model (RY = 56%)supported these findings, indicating that dead crown parts and fuel moisture content accounted formost of the variation in flammability parameters and greatly prevailed on terpenoid accumulationafter infection. The results of this study suggest that a disease can increase the flammability of trees.The deployment of canker-resistant cypress clones can reduce the flammability of cypress plantationsin Mediterranean areas aected by bark canker. Epidemiological data of diseased tree distributioncan be an important factor in the prediction of fire risk.