Relationships between Sphaerulina musiva Infection and the Microbiome and Metabolome.

Pathogenic fungal infections in plants may, in some cases, lead to downstream systematic impacts on the plant metabolome and microbiome that may either alleviate or exacerbate the effects of the fungal pathogen. While Sphaerulina musiva is a well-characterized fungal pathogen which infects tree species, an important wood fiber and biofuel feedstock, little is known about its systematic effects on the metabolome and microbiome of . Here, we investigated the metabolome of Populus trichocarpa and Populus deltoides leaves and roots and the microbiome of the leaf and root endospheres, phylloplane, and rhizosphere to understand the systematic impacts of abundance and infection on species in a common garden field setting. We found that is indeed present in both and , but abundance was not statistically related to stem canker onset. We also found that the leaf and root metabolomes significantly differ between the two species and that certain leaf metabolites, particularly the phenolic glycosides salirepin and salireposide, are diminished in canker-infected trees compared to their uninfected counterparts. Furthermore, we found significant associations between the metabolome, abundance, and microbiome composition and α-diversity, particularly in leaves. Our results show that colonizes both resistant and susceptible hosts and that the effects of on susceptible trees are not confined to the site of canker infection. Poplar ( spp.) trees are ecologically and economically important trees throughout North America. However, many western North American poplar plantations are at risk due to the introduction of the nonnative fungal pathogen , which causes leaf spot and cankers, limiting their production. To better understand the interactions among the pathogen , the poplar metabolome, and the poplar microbiome, we collected leaf, root, and rhizosphere samples from poplar trees consisting of 10 genotypes and two species with differential resistance to in a common garden experiment. Here, we outline the nuanced relationships between the poplar metabolome, microbiome, and , showing that may affect poplar trees in tissues distal to the site of infection (i.e., stem). Our research contributes to improving the fundamental understanding of and sp. ecology and the utility of a holobiont approach in understanding plant disease.