| With the acceleration of economical globalization,it will be expected that more and more invasive events of alien plants occurs worldwide,and the studies on the plant invasion has been becoming one of the hot research issues in the ecological field.In recent years,the Ageratina adernophora invasion has caused serious damages to agriculture,forestry,animal husbandry and even human life in China,and threatened the biodiversity of local ecosystems.The situation is extremely pressing for the prevention and control of A.adenophora expansion.At present,most of the studies have focused on impacts of A.adenophora on the macro-ecosystem,it is rare to explore the relationship between A.adenophora and local microbes.However,many literatures have indicated that pathogenic microbes can play an important role in plant community structure,ecological process and function,thus may act as the driving force of biological invasion and will influence the invasive process.Based on the above background,this study investigated the leaf spot disease incidence and collected the leaf spot fungal pathogens of A.adenophora populations in Yunnan,Guizhou and Guangxi Autonomous Region,which represent the different invasive histories.These fungal strains were isolated by traditional culture methods and identified by sequencing their ITS genes.Their pathogenicity on A.adenophora were verified by the inoculation experiment in wild.We tried to characterize,at the large geographical scale,the abundance,population structure,accumulation pattern,as well as the pathogenicity of leaf spot fungal pathogens of these A.adenophora populations.The following conclusions were primarily drawn:1.A total of 2751 leaf spot fungal strains of A.adenophora were isolated from 14 sample sites in Yunnan,Guizhou and Guangxi Autonomous Region.These strains were grouped into 216 OTUs based on their ITS(internal transcribed spacer)gene sequence at 97%of similarity.The top 10 dominant genera included Colletotrichum(26.90%),Xylaria(9.96%),Didymella(8.87%),Diaporthe(6.00%),Nemania(4.51%),Phoma(2.80%),Irpex(2.65%),Clonostachys(2.47%),Nigrospora(2.47%),Neofusicoccum(2.40%),accounting for 69.03%of totally isolated fungi.Furthermore,1160 strains were verified to pathogenic on A.adenophora by the inoculation experiment performed in field,and these pathogens included 57 genera.The top 10 dominant genera were Didymella(19.14%),Colotrichum(11.38%),Xylaria(9.91%),Nemania(8.53%),Diaporthe(5.34%)Pestalotiopsis(4.66%),Alternaria(4.14%),Phoma(3.10%),Neofusicoccum(2.93%)and Fusarium(2.84%),accounting for 54.31%of the tested 1876 isolates.2.The disease incidences were calculated by investigation of 760 A.adenophora individuals.Although the disease incidence was no statistical difference between those at the latest and at the middle invasive stage(P=0.906),the incidence at the latest stage was significantly lower than that at the middle,as well as that at the earliest invasive stage(P=0.000).Therefore,the disease incidence increased with the invasive history.Meanwhile,the abundance,diversity of leaf spot fungi and leaf spot fungal pathogens also increased with the invasive history.The fungal community structure was significantly different among A.adenophora populations in different invasive stages.Interestingly,the above parameters,such as fungal abundance and diversity,calculated from single leaf spot,decreased with invasive history.3.Fifteen types of leaf spot were identified from 238 leaf spots based on their color,form and leison location on the leaf.Each type of leaf spot harbored diverse and different fungi.In general,the fungi belonging to 41 genera contained both pathogenic and nonpathogenic strains,and the proportions of pathogenic/nonpathogenic strains for the top 15 dominant genera were Colletotrichum(17.84%),Xylaria(41.97%),Didymella(90.98%),Diaporthe(37.58%),Nemania(79.84%),Phoma(46.75%),Irpex(4.11%),Clonostachys(45.59%),Nigrospora(35.29%),Neofusicoccum(51.52%),Alternaria(77.42%),Pestalotiopsis(88.52%),Fusarium(66.00%),Schizophyllum(4.65%),Peniophora(65.85%).Among the remaining 43 genera,27 genera,like Corprinellus,were completely nonpathogenic but 16,like Ceratobasidium,were pathogenic.4.The virulence of these fungal pathogens were ranked into 11 levels based on their size of lesion on the leaf,including 0-20(mm~2),21-40(mm~2),41-60(mm~2),61-80(mm~2),81-100(mm~2),101-120(mm~2),121-140(mm~2),141-160(mm~2),161-180(mm~2),181-200(mm~2),and?2O1(mm~2).A total of 84.05%of 1160 pathogens showed the virulence less than the level 5.Among of top 5 dominant genera,Didymella showed the wide range of virulences across over all 11 levels,and 76.58%of strains had the virulence less than the level 6,but 12.61%of strains were high virulence which are distributed in the level 11.The virulence of other groups of pathogens were relatively weak and most strains were less than the level 3,including 95.45%of Colletotrichum,9].94%of Diaporthe,85.211%of Xylaria,and 77.78%of Nemania.5.The commonness and rarity of pathogens were evaluated by calculation of the percentage of pathogenic strains occurred in the total isolated strains.The common pathogens occurred across over different invasive stages were:Colletotrichum and Didymella;rare pathogens were Bipolaris,Corynespora,Epicoccum,Plectosphaerella,Pseudopithomyces,Trichoderma.Neither weak nor strong pathogenic strain was isolated from the latest invasive stage.The weak pathogenic strains in the middle invasive stage were Diaporthe,Gibberella,Irpex and Xylaria,and the strong pathogenic strains were Arthrinium,In the earliest invasive stage,the weak pathogenic strains were Schizophyllum but strong strains were Clonostachys.In conclusion,our data showed that the abundance,diversity of leaf spot fungi,as well leaf spot fungal pathogens,were positively related with the invasive history of A.adenophora.Our results will,firstly,provide a new theory and viewpoint,from the aspect of pathogen accumulation,for the further study on the invasive mechanism for successful invasion of A.adenophora,as well as other invasive plant systems.Secondly,this data will facilitate the understanding novel pathogen spread with the A.adenophora expansion in local ecosystem and guide the epidemic disease control and prevention for local crop system.Finally,the evaluation of pathogenic virulence and host range of these strains will build the fundamental for the development of biocontrol on the A.adenophora invasion in future. |
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