Abstract
To study simultaneous biotic and abiotic stress effects on monoterpene mediated defence response, four-year-old seedlings of two clones of Picea abies (c386: “relatively resistant” c386; c171: “relatively susceptible” clone 171) were inoculated with an isolate of rot fungus Heterobasidion parviporum and simultaneously subjected to a drought stress recovery cycle. Fungal growth into the wood was generally higher in well-watered (W) than in drought-stressed (D) plants. As predawn water potential decreased, gas exchange and maximal photochemical efficiency of PSII also declined. Water potential and chlorophyll fluorescence showed differences between clones in D plants, c386 being more tolerant than c171, while stomatal conductance and net photosynthesis differed between clones in W plants; c171 showing higher values than c386. A recovery of physiological functions was observed after re-watering. The clones showed different constitutive monoterpene profiles. The infection generally caused some extensive compositional changes in the relative contents of several monoterpenes and their enantiomers; also, sterile infection (wounded only samples) affected the relative proportions of monoterpenes, although to a lesser extent than reactions elicited by the fungus. The trend in monoterpene response to disease treatments was the same in D and W plants of both clones. In particular, higher proportion of δ-3-carene was found constitutively in c386 in comparison with c171; besides, infection with H. parviporum increased the relative contents of δ-3-carene in all the samples, even if proportions of this monoterpene in wounded plus inoculated tissues of c386 were significantly higher than cortical tissues from non-inoculated branches only in W seedlings 44 days after treatment. Although drought stress decreased the total absolute contents of monoterpenes, total monoterpene concentrations significantly increased in response to infection by H. parviporum. © 2018