Studies On Taxonomy And Diversity Of Endophytic Fungi From Cucurbit Plants

Endophytic fungi are widely colonized in plants and play an important role in increasing the fitness of plant hosts by enhancing their resistance to abiotic and biotic stresses.This dissertation mainly focuses on molecular identification of endophytic fungal strains isolated from cucurbit plants in our laboratory.In order to learn more about the diversity of endophytic fungi in cucumber,the endophytic mycobiota in different tissues of cucumber were analysed by using culture-independent method.The main results in this study are listed below.1.Based on BLAST analysis of ITS sequences in GenBank,232 fungal species belonging to 84 genera were identified from 1591 fungal strains,including eight possible new species.Phylogenic analysis based on ITS sequences revealed that the endophytic fungal strains mainly belong to Ascomycota,especially Capnodiales,Pleosporales,and Botryosphaeriales in Dothideomycetes,Glomerellales,Hypocreales,and Sordariales in Sordariomycetes,Eurotiales in Eurotiomycetes.2.Phylogenic analysis of the strains,belonging to Phialemoniopsis,Plectosphaerella,and Talaromyces,respectively,revealed that four new species Ph.endophytica,Pl.sinensis,T.cucurbitiradicus and T.endophyticus based on multi-locus DNA sequences.The systematic placements of some species and the differences between similar species in related genera were discussed according to the results of molecular and morphological studies.The endophytic strains in Plectosphaerella belong to Pl.cucumerina and Pl.sinensis.The endophytic strains in Talaromyces belong to six species,i.e.T.cnidii,T.pinophilus,T.radicus,T.wortmannii,T.cucurbitiradicus and T.endophyticus.In addition,the species circumscriptions in Plectosphaerella were further clarified,the values of nucleotide polymorphisms of sequences were verified in taxonomy of Talaromyces species.Eighty-four strains were deposited in Agricultural Culture Collection of China(ACCC)and 201 DNA sequences were submitted in GenBank.3.Based on the high-throughput sequencing analysis,there were 919 OTUs of endophytic fungi in cucumber roots,stems and leaves,mainly composed of ascomycetes(69.21%)and basidiomycetes(24.81%).Pleosporales is widely distributed in different tissues and richest in leaf,the dominant genus is Alternaria.Glomerellales,Sordariales and Saccharomycetales are dominant in root.The diversity of endophytic fungi from the roots,stems and leaves were ananlyzed.The average of Chao1 indexs were 448.77,285.01 and 270.85 respectively.The average of Shannon diversity indexs were 5.23,3.20 and 2.70,respectively.The results further clarified the species constitution and main taxonomic groups of the endophytic fungi from cucurbit plants,discovered several new species,and preliminarily revealed community and diversity of endophytic fungi in different parts of cucumber plant,which provides a basis for understanding ecological fuction of endophytic fungi in cucurbit plants.