Impacts of Dutch elm disease–causing fungi on foliage photosynthetic characteristics and volatiles in Ulmus species with different pathogen resistance.

This article investigates the physiological responses of two Northern European elm species, Ulmus glabra (more vulnerable) and Ulmus laevis (more resistant), to mechanical injury and inoculation with Dutch elm disease (DED)-causing fungal pathogens Ophiostoma novo-ulmi subsp. novo-ulmi and O. novo-ulmi subsp. americana. The study monitored leaf-level photosynthetic traits and emissions of biogenic volatile organic compounds (VOCs) over 12 days post-inoculation. Results showed that photosynthesis remained stable in both species, but stomatal conductance decreased temporarily only in U. glabra, indicating greater susceptibility. In contrast, U. laevis exhibited a stronger pathogen-induced increase in VOC emissions, particularly lipoxygenase pathway volatiles, suggesting a more robust defense activation. These findings imply that the higher DED resistance of U. laevis may be linked to its stronger volatile-mediated defense responses, although such emissions could also influence attraction of insect vectors under climate change scenarios.