Diversity and pathogenicity of Alternaria species associated with the invasive plant Ageratina adenophora and local plants

Pathogen accumulation after introduction is unavoidable for exotic plants over a long period of time. Therefore, it is important to understand whether plant invasion promotes novel pathogen emergence and increases the risk of pathogen movement among agricultural, horticultural, and wild native plants. In this study, we used multiple gene analysis to characterize the species composition of 104 isolates of Alternaria obtained from the invasive plant Ageratina adenophora and native plants from Yunnan, Hubei, Guizhou, Sichuan, and Guangxi in China. Phylogenetically, these strains were from A. alternata (88.5%), A. gossypina (10.6%) and A. steviae (0.9%). There was a high amount of sharing between strains associated with A. adenophora and with local plants. Pathogenicity tests indicated that most of these Alternaria strains are generalists; the isolates with a wider host range were more virulent to the plant. Woody plants were more resistant to these strains than herbaceous plants and vines. However, the invasive plant A. adenophora was highly sensitive to these strains. Our data are valuable for understanding how A. adenophora invasion impacts the Alternaria species composition of the native plant and whether A. adenophora invasion causes potential disease risks in invaded ecosystems.