| Ageratina adenophora(Spreng.)R.M.King et H.Rob.,as one of the most seriously invasive plants in Southwestern China,has caused large-scale economic and ecological damages in the invaded area.In recent years,a large number of pathogenic fungi belonging to family Didymellaceae have been isolated from the leaf spots,as well as the sourrounding environments of A.adenophora.In this study,the species composition and distribution of these Didymellaceae fungi were determined.Then,their pathogenicity on A.adenophora and native plants were tested and the potential ecological risks in the invasive area were anaylised.Futhermore,the potential biocontrol fungi of A.adenophora were screened and their whole genomes were sequenced.Finally,the possible fungal transmission patterns in the environment were verified.The main conclusions were obtained as followings:1.Based on the multiple genes analysis of the large subunit of the ribosomal RNAs(LSU),the first internal transcribed spacer(ITS),the RNA polymerase II second largest subunit(rpb2)and the partial?-tubulin(tub2),213 Didymellaceae isolates belonged to 10known genera and 2 potential novel genera,accounting for nearly half of the 25 known genera in this family.Five numerically dominant genera were Epicoccum,Didymella,Remoteididymella,and two potential novel genera D1 and D2,accounted for 92%of the total isolates.Among of them,group D1 and genus Epicoccum accounted for 38%,and 27%of the total isolates,respectively.Combining multiple genes analysis with morphological characteristics,three potential novel species belonging to genus Remotididymella were identified,named as R.speciosa,R.ageratinae,and R.anemophila,respectively.2.Using an inoculation experiment in field and greenhouse,the pathogenicity of these fungi on A.adenophora and native plants were tested,and their virulence and host range were characterized.Averagely,the strains from group D1 and D2 showed weak virulence to native plants but strong virulence to A.adenophora;meanwhile,these fungi showed the narrow host range of native plants.Therefore,A.adenophora does not completely escape from natural enemies in the invaded area and still harbours certain host-specific fungal pathogens.Moreover,the isolates from genera Epicoccum and Boeremia showed high pathogenicity to native plants and A.adenophora,with the size of leaf spots more than 70mm~2;meanwhile,the isolates were widely isolated from invasive plants,as well as from native plants.These data indicate that the fungal pathogens associated with A.adenophora are highly possible for transmitting to native plants and thus cause great disease risks.In addition,although the strains from one genus varied in the pathogenicity,the strains belonging to different genera was statitcially significant in the pathogenicity.There was no a co-evolutionary relationship between pathogenic fungi and their corresponding hosts.Finally,two potential biocontrol fungi,i.e.,Y122 and S188,were screened using a quantitative assay of pathogenicity.3.Genomic sequencing was performed on the potential biocontrol strain Y122,as well as a weakly pathogenic strain G168,which is treated as a control.The genomes of 38.46 Mb and37.71 Mb were obtained for Y122 and G168,respectively.The analysis of gene function indicated that these two fungal strains harboured abundant carbohydrate active enzymes,including the glycoside hydrolase(>200 gene)and polysaccharide lyase(>30 gene),with a characteristic of both virulent pathogenic fungi and saprophytic fungi.A comparison of these two genomes revealed that the strain Y122 contained the unique gene(GO:0009403),which may be responsible for determing the virulence,and gene GH5?12,GH5?22,GH36 and GH95,which may be responsible for determing the host range.4.The high-throughput sequencing technology was used to characterize the differences of fungal community in the canopy air between native plants in non-invaded area and the invasive plant A.adenophora.The main fungal groups in the air were Cladosporiaceae(63.65%),Nectriaceae(9.54%),Pleosporaceae(5.34%),Didymellaceae(3.22%),Subcreales(3.21%),Cordycipitaceae(1.92%),Mycosphaerellaceae(1.17%),and Aspergillaceae(1.14%).The?-diversity of fungi in the canopy air of A.adenophora was significantly higher than that of native plants in the non-invaded area.Compared with native plants in non-invaded area,the Didymellaceae fungi were more abundant in the canopy air of A.adenophora,nearly more than four times of those in the canopy air of native plants.In addition,we found that the fungi from family Didymellaceae co-occurred more frequently with themselves than with other fungi.This pattern may be related to the high capacity of Didymellaceae spores in the canopy air of monoculture invasive plant A.adenophora.Finally,it was confirmed that Didymellaceae fungi were the primary airborne pathogen of A.adenophora by a shared comparison between the leaf spot pathogens of A.adenophora and the fungal pool obtained from high-throughput sequencing.In conclusion,our study has greatly improved the understanding of the interaction mechnisms between the invasive plant A.adenophora and fungal pathogens in the invaded area.It is also important for evaluation of ecological risk driven by fungi associated with A.adenophora.In addition,the data provide a foundation for the development of biocontrol fungi of A.adenophora in future. |
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