Pathogen/host relationships in wild plant communities are influenced by many biotic and abiotic factors, making them difficult to study in the field. Climate change could further complicate matters by altering host susceptibility, pathogen virulence, or shifting the phenology of either actor. Studies of outbreaks enabled by unusual weather conditions could provide insight into how these pathogen/host interactions might behave in future climate regimes. However, documented studies of this type are rare.
In 2015, an unusually warm, wet spring enabled a widespread natural outbreak of the fungal pathogen
Results/Conclusions
Drepanopeziza caused severe necrosis in the leaf tissue of infected clones, stimulating the production of a compensatory second flush of leaves in mid-summer. Gas exchange in diseased clones was reduced by over 50% in first flush leaves, but increased by nearly 50% in second-flush leaves. Infection was strongly correlated with reduced foliar phenolic glycoside concentration and early budbreak in aspen clones. Susceptibility was likely determined by a combination of weakly defended leaves and unusual rainfall that coincided with early budbreak in the spring of 2015. Climatologists predict that the weather patterns we observed in 2015 may become more common in the future; this could alter the dynamics of this pathogen-host relationship and increase biotic stress on aspen, which is already declining in large portions of the Intermountain West.