Changes in leaf chemistry and anatomy of Corymbia citriodora subsp. variegata (Myrtaceae) in response to native and exotic pathogens

Corymbia citriodora subsp. variegata (CCV) is an economically and ecologically important timber species, native to eastern Australia. It is highly susceptible to Quambalaria pitereka, a coevolved endemic pathogen, and Austropuccinia psidii, an exotic invasive pathogen. Genes associated with resistance to Q. pitereka are specific and uncorrelated with the genes associated with resistance to A. psidii , suggesting different resistance mechanisms to each pathogen, possibly associated with leaf phenotypic traits. This study examined leaf chemical and anatomical differences in CCV between uninoculated plants and those inoculated with Q. pitereka and A. psidii . The results demonstrate that the pathogens induce different responses in CCV. Plants inoculated with A. psidii exhibited chemical and anatomical changes that were not observed in uninoculated controls and Q. pitereka- inoculated plants, such as deposition of polyphenols and tannins in upper/lower epidermis, variation in the proportion of monoterpenes, steroids, monounsaturated hydrocarbons and long chain hydrocarbons and higher leaf toughness. In contrast, CCV response to Q. pitereka altered the distribution of polyphenols and tannins in the leaves and possible accumulation of these compounds and lignin in necrotic areas. These findings provide a better understanding of factors underlying CCV responses to coevolved and exotic pathogens and add insights into plant-pathogen interactions.