Quantifying the sharing of foliar fungal pathogens by the invasive plant Ageratina adenophora and its neighbours.

Local pathogens can accumulate as asymptomatic endophytes, making it difficult to detect the impacts of invasive species as propagators of disease in the invaded range. We used the invasive plant Ageratina adenophora to assess such accumulation. We intensively collected foliar fungal endophytes and leaf spot pathogens of A. adenophora and co-occurring neighbours and performed an inoculation experiment to evaluate their pathogenicity and host range. Ageratina adenophora harboured diverse necrotrophic pathogens; its communities of endophytes and leaf spot pathogens were different in composition and shared only a small number of fungal species. In the pathogen communities of local plant hosts, 21% of the operational taxonomic units (OTUs), representing 50% of strains, also occurred as leaf spot pathogens and/or endophytes of A. adenophora. The local pathogen community was more similar to the endophytes than to the pathogens of A. adenophora. The inoculation experiment showed that local pathogens could infect A. adenophora leaves asymptomatically and that local plant hosts were susceptible to both A. adenophora endophytes and pathogens. Ageratina adenophora is a highly competent host for local pathogens, and its asymptomatic latent pathogens are fungi primarily shared with local neighbours. This poses challenges for understanding the long-term ecological consequences of plant invasion.

Tissue-Specific and Geographical Variation in Endophytic Fungi of Ageratina adenophora and Fungal Associations With the Environment.

To understand the distribution of the cultivable fungal community in plant tissues and the associations of these fungi with their surrounding environments during the geographical expansion of an invasive plant, Ageratina adenophora, we isolated the cultivable fungi from 72 plant tissues, 12 soils, and 12 air samples collected from six areas in Yunnan Province, China. A total of 4066 isolates were investigated, including 1641 endophytic fungi, 233 withered leaf fungi, 1255 fungi from air, and 937 fungi from soil. These fungi were divided into 458 and 201 operational taxonomic units (OTUs) with unique and 97% ITS gene sequence identity, respectively. Phylogenetic analysis showed that the fungi belonged to four phyla, including Ascomycota (94.20%), Basidiomycota (2.71%), Mortierellomycota (3.03%), and Mucoromycota (0.07%). The dominant genera of cultivable endophytic fungi were Colletotrichum (34.61%), Diaporthe (17.24%), Allophoma (8.03%), and Fusarium (4.44%). Colletotrichum and Diaporthe were primarily isolated from mature leaves, Allophoma from stems, and Fusarium from roots, indicating that the enrichment of endophytic fungi is tissue-specific and fungi rarely grew systemically within A. adenophora. In the surrounding environment, Alternaria (21.46%), Allophoma (19.31%), Xylaria (18.45%), and Didymella (18.03%) were dominant in the withered leaves, Cladosporium (22.86%), Trichoderma (14.27%), and Epicoccum (9.83%) were dominant in the canopy air, and Trichoderma (27.27%) and Mortierella (20.46%) were dominant in the rhizosphere soils. Further analysis revealed that the cultivable endophytic fungi changed across geographic areas and showed a certain degree of variation in different tissues of A. adenophora. The cultivable fungi in mature and withered leaves fluctuated more than those in roots and stems. We also found that some cultivable endophytic fungi might undergo tissue-to-tissue migration and that the stem could be a transport tissue by which airborne fungi infect roots. Finally, we provided evidence that the fungal community within A. adenophora was partially shared with the contiguous environment. The data suggested a frequent interaction between fungi associated with A. adenophora and those in surrounding environments, reflecting a compromise driven by both functional requirements for plant growth and local environmental conditions.