| Cytospora(teleomorph Valsa) is one of the important tree canker pathogen in the world, caused significant losses to forest ecosystems in the north of China. Taxonomic researches of this pathogen were relatively weak in China; the issues included that inaccurate identification, incompleted description, incomprehensive distribution and host lineage, as well as synonyms and homonyms. Based on 102 Cytospora isolates on 33 hosts obtained from 4 typical climatic regions in China, morphology and culture characteristics observation were conducted, and phylogenetic analyses were carried out as well. Two new records and a new species were found. Phylogenetic analyses according to the DNA sequences and ITS1 secondary structure studied synonyms and homonym in Cytospora and the relationship of intraspecific genetic differentiation with host, climate and geographic distribution in some widely-distributed species. This study provided important morphological and molecular evidence for the identification of Cytospora and offered important scientific basis about quarantine, forecast, V and epidemic pattern to the pathogens. The conclusions obtained as follows:1. According to morphological evidence and culture trait, the 102 isolates were identified as six species, i.e., C. chrysosperma, V. germanica, V.malicola, C. tritici, V. mali(anamorph C. sacculus, synonym V. ceratosperma) and an unknown species, and were described in detail. EF1-a and β-tubulin phylogenetic analyses verified the identification, delimited “species complex” into two well supported monophyletic clades respectively, which could not be resolved using r DNA-ITS phylogenetic analyses.2. This study identified the unknown species as a new species morphologically and phylogenetically, and nominated Cytospora palm sp. nov., described in detail as well. In culture, conidiomata often grew together, circular, erumpent, 2.84 ± 1.25 mm diam.; locule subudivided by invaginations, up to 7-10 unregular arranged chambers sharing common walls(rosette cytosporoid). Necks level to 1-3 mm above the disc surfaces. Conidiophores hyaline, unbranched or occasionally branched at base, 11.02 ± 2.28 × 1.30 ± 0.15 μm. Conidia hyaline, eguttulate, allantoid, aseptate, 4.36 ± 0.25 × 1.24 ± 0.18 μm.3. The phylogenetic analysis based on the combined sequence-structure information improved the resolution of phylogenetic analyses in closely related spcies in Cytospora. The result showed that Chinese V. mali were differentiated into two variants: V. mali var. mali and V. mali var. pyri. The following sprcific names in brackets were reduced to synonyms of the former namers: V. mali var. mali(V. ceratosperma sensu Kobayashi), V. mali var. pyri(V. ceratosperma). V. ceratosperma sensu Kobayashi, V. ceratosperma and other three namesakes to V. ceratosperma in Gen Bank were homonyms.4. C. chrysosperma accounted 83 % of all isolates, which indicated it was a dominant species in this study. According to multigene phylogenetic analyses of 46 C. chrysosperma isolates, the genetic divergences were proposed and the differentiation had a strong correlation with climatic regions of the isolates. Reconstruction of ancestral distribution and geographical distribution statistics showed the ratiocination about the original centers, major distribution centers and genetic diversity center of C. chrysosperma.In summary, this study used morphological and phylogenetic methods to identify and describe the pathogens, found two new records and a new species, enriched species diversity of Cytospora. Phylogeny analyses of multigene and secondary structure improved the accuracy of molecular identification, clarified phylogenetic relationship of the species in this study. |
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