Phylogeny And Taxonomy Of Cytospora In Yellow River Region Of China

Cytospora species are important phytopathogens causing severe canker disease with a worldwide distribution and broad host range with more than 85 plant species. The canker disease of Eucalyptus, Malus, Populus and Salix associated with Cytospora species are the most harmful diseases threating the health of these trees, even dead, which lead to severe economic and ecological losses.A total of 110 species epithets named Cytospora have been recorded and 31 epithets were recognized in China. The traditional identification of Cytospora species was based mainly on their host affiliations, often with vague morphological descriptions whereas the host-specificity of some Cytospora species is not stable. In addition, most species lack available type speciemens and ex-type strains, as well as DNA data and backbone tree, which has led to confusions of identification and overmuch specific epithets with unidentified speices, hosts and distributions. Cytospora has been considered as asexual state of Valsa, Leucostoma, Valsella and Valseutypella, which have been treated as the synonyms of Cytospora. Few significant study of taxonomy could cause great difficult to identifications of species, diagnosis and control of fugal diseases derictly. Therefore, the aim of the present study was to delimit the species associated with canker disease in Yellow River region of China based on widely investigations and collections of fresh specimens; and to establish the taxonomic system of Cytospora based on morphological observation and phylogenetic analysis.The land resources of Yellow River region are abundant and have been regarded as an important forest protected areas with high disease frequency. In the current study,700 isolates were collected from ca.684 specimens on various hosts, which included 45 species residing in 25 genera of 14 families from Yellow River region of China. Morphological observation includes shape of fruit bodies in branches or twigs, size of conidia and ascospores and cultural characteristics. Phylogenetic analysis consist of MP, ML and Baysian methods based on two ribosomal genes and four genes coding proteins to analysis the connections and evolution in Cytospora. The conclusions in the current study are below.1. Clarify the morpholocal key to Cytospora species. Six groups were proposed based on morphology of conidiomata. Group I was characterized by conidiomata has single locule and single ostiole with present black conceptacle. Group I was characterized by conidiomata has single locule and single ostiole with black conceptacle. Group II was characterized by conidiomata has multiple locules and single ostiole with black conceptacle. Group III was characterized by conidiomata has multiple locules and multiple ostioles with black conceptacle. Group IV was characterized by conidiomata has multiple locules and single ostiole without black conceptacle. Group V was characterized by conidiomata has single locule and single ostiole without black conceptacle. Group VI was characterized by conidiomata has multiple locules and multiple ostioles without black conceptacle. Of which multiple locules separated to two subgroups according to individual or sharing the walls of locules. Besides, cultural characteristics, size of conidia and sexual morph were important morpholocal key, as well as some special structures and hosts.2. Describe the morphology and habitat of 22 Cytospora species and clarify the species, distributions and host range of Cytospora in Yellow River region. Of which seven Cytospora were new species, i.e., Cytospora berberidis, C. gigalocus, C. gigaspora, C. pruinopsis, C. rostrate, C. sibiraeae, C. sophoricola. The most common species is C chrysosperma distributed in Salicaceous plants in many provinces we investigated.3. Analyze the relationship of Cytospora species using multigene phylogeny. The phylogram was performed by Maximum Parsimony (MP), Maximum Likelihood (ML) and Bayesian Inference (BI) based on internal transcribed spacer (ITS), ribosomal RNA large subunit (LSU), actin (act), RNA polymerase II second largest subunit (rpb2), translation elongation factor 1-alpha (tefl-a) and beta-tubulin (tub) genes. The results indicated ITS, LSU, act, rpb2, tefl-a and tub have significant inter-and intra-distince to indentify differentiation of Cytospora. Therefore, the selected six genes could be used for rapid identification to Cytospora species as the DNA barcoding candidate.4. Clarify Cytospora species diversity in willow, popular, walnt, elm and China scholar tree hosts. Willow canker disease was caused by Cytospora chrysosperma, C. nivea, C. populina and C. rostrate. Cytosproa atrocirrhata, C. chrysosperma, C. gigalocus and C. sacculus were responsible for walnut canker disease. Cytospora carbonacea, C. chrysosperma, C. pruinopsis and C. ribis were associated with elm canker disease. Cytospora chrysosperma, C. sophorae and C. sophoricola were found in China sholar trees with various symptom of canker or dieback desease. The current study also represents that Cytospora chrysosperma could infect Ulmus spp., Styphnolobium spp., Rhus typhina, Cornus alba and Fraxinus chinensis for the first time and common hosts Populus spp., Salix spp.