Aim

Recent research has highlighted that the relationship between species interactions and latitude can differ between native and invasive plant taxa, generating biogeographical heterogeneity in community resistance to plant invasions. In the first study with foliar pathogens, we tested whether co-occurring native and invasive lineages of common reed (Phragmites australis) exhibit nonparallel latitudinal gradients in foliar fungi communities, pathogen susceptibility and damage, and whether these biogeographic patterns can influence invasion success.

Location North America.

Time period 2015-2017.

Major taxa studied Perennial grass Phragmites australis.

Methods We surveyed 35 P. australis field populations, spanning 17° latitude and comprising four phylogeographic lineages, including one endemic to North America and one invasive from Europe. For each population, we quantified percent leaf pathogen damage and cultured fungi from diseased leaves, that we identified using molecular tools. To assess whether latitudinal gradients in pathogen damage were genetically-based, we inoculated plants from 73 populations with four putative pathogens in a complementary common garden experiment, and measured P. australis susceptibility (i.e., diseased leaf area).

Results We isolated 84 foliar fungi morphospecies. Phragmites australis lineage influenced fungal community composition but not diversity. Despite the invasive European P. australis lineage being the least susceptible to three of the four pathogens tested in the common garden experiment, pathogen damage in the field was similar between native and invasive lineages, providing no evidence that release from foliar pathogens contributes to invasion success. Genetically-based latitudinal gradients in pathogen susceptibility observed in the common garden were isolate-specific and obscured by local environmental conditions in the field, where pathogen damage was threefold higher for northern than southern populations, regardless of lineage.

Main conclusions Our results highlight that host plant lineage and genetically-based biogeographic gradients strongly influence foliar fungi communities and pathogen susceptibility, but do not translate to pathogen damage patterns observed in the field.

Methods provided in corresponding paper.

Please contact corresponding author if further information is required.