Climatic origin of provenances of Corymbia calophylla affects canker disease susceptibility, caused by Quambalaria coyrecup , and interactions with drought stress

Many forest ecosystems are in decline around the world due to increasing biotic and abiotic stresses. Marri (Corymbia calophylla) is an endemic and common eucalypt species of southwestern Australia, which is in decline primarily due to stem canker caused by the pathogenic fungus Quambalaria coyrecup. This study determined to what extent disease susceptibility and plant growth were associated with climate at origin for eight provenances of marri. Plants of all provenances were grown in a common garden with or without pathogen inoculation. Disease development and physiological performance of plants were monitored during an initial irrigated and subsequent terminal drought period. Provenances from drier regions were more susceptible to the fungal pathogen than those from wetter regions, having on average 31% higher incidence rates at 20 days post-inoculation (dpi) and larger canker lesions at 130 dpi (on average 49% increase) and 230 dpi (on average 42% increase). However, canker development for each provenance was fastest during the initial irrigated wetter growing period. Overall, the average relative canker growth rate was 4-fold higher during the irrigated period compared to the terminal drought period (p .05). Canker infection reduced both photosynthetic rates and growth rates but only during the later part of the terminal drought period, with significant (p < .05) reductions observed in two out of eight provenances, when plants had relatively large canker sizes. This effect tended to be strongest in the provenances from drier regions as they had relatively larger canker sizes than the provenances from wetter regions. We propose that the increased susceptibility of drier provenances is related to their lower exposure to the pathogen in their drier habitats. Since this is potentially due to suboptimal defence responses, using provenances from drier locations to ‘future-proof’ local restoration outcomes in a drying climate may be counterproductive due to plant–pathogen interactions