Juglans nigra Targeted loci environmental
Thousand Cankers Disease incidence and severity is higher in the introduced range of Juglans nigra in the Western U.S. We hypothesized that these differences are driven in part by geographical variation in the host phytobiome and its known functions in host stress tolerance, nutrient acquisition, and defense. To begin characterizing the role of the phytobiome in mediating Thousand Cankers Disease incidence, we evaluated differences in the J. nigra phytobiome in portions of the host's native (Indiana and Tennessee) and introduced range (Washington) across grafted clones and open-pollinated populations present in each state. DNA was extracted from bulk soil and branch (caulosphere) tissues and ITS and 16S regions were sequenced for characterization of fungal and bacterial communities. We found that fungal and bacterial communities in the caulosphere and soil differ between the native and introduced range of J. nigra and harbor different mutualistic and pathogenic microorganisms. Additionally, caulosphere fungal and bacterial communities were more species-rich and diverse in the native range of J. nigra, suggesting that plant-associated microbial communities in the host's native range possess greater levels of functional redundancy and multifunctionality compared to the introduced range. We also found higher network complexity in the caulsophere of trees in the introduced range and evidence for two alternative stable community states associated with diseased and healthy trees. Our results provide support for the hypothesis that geographical variation in Thousand Cankers Disease incidence and severity is partially driven by differences in the phytobiome of J. nigra in its introduced and native range.