Genetic Structure Of Colletotrichum In The Invaded Area Of Ageratina Adenophora In Yunnan Province

Plant diseases have always been one of the important factors to limit high quality and yield of crops,and in most cases plant diseases are commonly caused by pathogenic fungi.Genus Colletotrichum contains many species,with a wide range of hosts.It is widely distributed in tropics and subtropics,and causes many diseases of crops,woody plants,herbs and fruits.Studies on Colletotrichum have currently focused on strains isolated from crops and ornamental plants.However,it remains to be explored the differences in species composition,as well as the genetic communication between Colletotrichum populations of invasive and native plants.In this study,firstly,Ageratina adenophora from 14 invaded areas in Yunnan Province,both its healthy and diseased leaves,were investigated and collected.Meanwhile,the diseased leaves of native plants in these areas were also collected.Totally,874 strains of Colletotrichum were obtained using traditional isolation and culture techniques,by the molecular identification of ribosomal transcribed spacers gene(ITS).Multiple genes,including Actin gene(ACT),Glyceraldehydes-3-phosphate dehydrogenase gene(GAPDH),Chitin synthase A gene(CHS-1),?-Tubulin 2 gene(TUB2),Calmodulin gene(CAL)and Glutamate synthase gene(GS)were further amplified for those dominant ITS genotypes,including OTU48 and OTU397.Phylogenetic species were identified by using the genealogical concordance phylogenetic species recognition.Then,population genetics,population expansion,and pedigree geographic structure of the Colletot.richum gloeosporioides complex,Colletotrichuwm kahawae subsp.Ciggaro and Colletotrichurmfructicola were analyzed by the methods of population genetics.The evolutionary history of the populations of the Colletotrichurym gloeosporioides complex and the cause of their modern geographical distribution pattern were reasoned.Finally,we compared them with those pathogens Colletotrichum of commercial crops from other parts of the world.The main results and conclusions were as follows:1.Colletotrichum isolated from the healthy,diseased leaves of A.adenophora,as well as the diseased leaves of native plants in the invaded area in Yunnan Province showed high diversity of species.874 strains of Colletotrichum belonged to 72 ITS genotypes.Multiple-gene analysis using Bayesian method and maximum likelihood method showed that 304 strains from the dominant ITS genotypes belonged to the C gloeosporioides complex.However,the strains from different isolation sources,including geographic sites and plant sources,were admixed in the whole phylogenetic tree.The results indicated that Colletotrichum accumulated by A.adenophora had similar species composition with those from the leaf spots of native plants.It suggested that the pathogenic Collelotrichum from native plants in the invaded areas could be accumulated by A.adenophora in the form of endophytes and leaf pathogenic fungi.2.Gene flow was verified to be common among Colletotrichum populations from geographical sites with many natural obstacles.Gene flow was more frequent among neighbour populations with close geographical distances,and among those located in the developed transportation networks.Compared with other regions,the central part of Yunnan Province showed higher genetic diversity of Colletotrichum,and maybe acted as the main crossover for gene flow of Colletotrichum.Although most of the strains were isolated from A.adenophora,their spreads showed no correlation with the invasive history of A.adenophora.3.In Yunnan Province,the C gloeosporioides complex was a large and stable population,which has accumulated high genetic variation after experiencing a long period of evolution.However,the dominant phylogenetic species C.kahawae subsp.Ciggaro and C.fructicola experienced population expansion due to the selection pressure from the heterogeneous geographical environments.It suggests that some phylogenetic species of Colletotrichum in the invaded areas of A.adenophora is undergoing rapid differentiation and population expansion.4.There were the shared 12 genotypes of Colletotrichum in the invaded area of A.adenophora in Yunnan Province and those of other economic crops worldwide,accounting for 16.67%of the total genotypes;they contain 383 strains,accounting for 43.82%of the total strains.It suggests that A.adenophora does not only compete habitat sources with the native plants in the invading area during its invasive process,but also facilitate the spread of Colletotrichum,which may bring new diseases to the commercial crops in the invaded areas.Our results will help people to understand the impact of A.adenophora invasion on the structure of pathogenic fungi of Colletotrichum in the local plant ecosystem and potential ecological risks,and provide clues for future research on the role of microorganisms in the invasion process of other plant systems.It also laid a preliminary foundation for assessing the effects of exotic plants on the distribution,evolution and spread of new Colletotrichum strains in local plants,and was important for guiding the development and application of new plant resistant varieties in the future.