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

Abstract

Summary 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.

Virulence evolution of multiple infections with vertically and horizontally transmitted fungal species in a natural plant system

“…Further experiments indicated that 25.3% of foliar pathogens were seedborne ( Fig. 2a, Raw data), including one dominant pathogen, OTU1 (Allophoma cylindrispora, family Didymellaceae; an unidentified OTU515 was observed in our previous report (Chen et al 2020b)), accounting for 15.6% of total foliar pathogens (Raw data).…”

“…We focused our multiple infections at the leaf spot level, rather than the host individual level, because (i) a multiple infection within-leaf spot should include both direct and indirect interactions of pathogens (Tollenaere et al 2016) and (ii) multiple fungal species or genotypes from one species have been observed to co-occur in the same spots of Eucalyptus (Crous et al 2009, Perez et al 2010; thus, multiple infections in one leaf spot should be common but remain to be characterized. Previously, we reported the foliar pathogen sharing of A. adenophora with local plants in Yunnan Province, which is a relatively old invasion area (Chen et al 2020b). In this case, we expanded the sampling areas into two newly established neighbouring provinces, Guizhou and Guangxi.…”

“…Mothur 1.35.1 with the Naï ve Bayesian classifier was used to identify the remaining sequences (database, UNITE_public_mothur_full_04.02.2020 (Abarenkov et al 2020)) and to group the consensus sequences into operational taxonomic units (OTUs) at 100% sequence identity (Schloss et al 2009). Because different trimming of alignment and the updated version of UNITE database were used in this analysis, which caused changes partially in the delimitation and phylogeny of OTUs that previously reported (Chen et al 2020b), these ITS sequences were resubmitted and all nucleotide sequences reported in this study were deposited at GenBank under the accession numbers MT908377-MT908827(also see Raw data).…”

“…We first tested the virulence of all isolated fungi on host A. adenophora. The inoculation experiment was performed as previously reported to test the virulence of necrotrophic pathogens in tropical forests (Gilbert and Webb 2007) with minor modifications, as detailed in a previous report (Chen et al 2020b). Each fungal strain was inoculated into five mature and healthy leaves from a single individual of A. adenophora to test pathogenicity.…”

“…There is evidence that A. adenophora can infect fungal pathogens in the introduced ranges (Zhou et al 2010, Poudel et al 2019). In particular, our recent study indicates that A. adenophora accumulates diverse foliar pathogens from neighbours (horizontally transmitted); however, a primary pathogen (OTU515), which belongs to the family Didymellacea, does not occur on surrounding native plants (Chen et al 2020b). Thus, we hypothesize that this pathogen may be cospread with the host by seeds (vertically transmitted) because A. adenophora disperses primarily by wind and water through minute asexual seeds (Wang et al 2011).…”