ITS-nrDNA sequence study of important species in genus Cytospora

摘要

ITS sequences of Cytospora, combined the related sequences in GenBank, were analyzed by Neighbor Joint Method of Software Mega 4.0. The results show that all tested Cytospora isolates can be divided into two groups, and five subgroups in Group1. Group 2 is a mixture group of poplar rot pathogens and pear rot pathogens. The first subgroup in Group1 is eventually poplar Cytospora pathogens. The second subgroup is made of pathogens of apple rot pathogen and pear rot pathogen. The third subgroup is Cytospora cincta. The fourth subgroup is Lecucotosma persooni, while the fifth subgroup is the rot pathogens all from host Populus cathayana. The overall diversity of Cytospora sequences is 0.1789, Tajima-Nei value is 0.254762, which manifests Cytospora is a species deviated from Hardy-Weinberg Balance, and positive mutant events in the progress of evolution are distinguished. The effects of environment factors to the evolution progress are dominated. Poplar Cytospora pathogens from China are subjected to 3 clusters, total diversity of intra-species sequences is 0.180102, Tajima-Nei value is 0.139, which also imply the positive mutant events in the evolution progress. Most isolates of Cytospora chrysosperma are subject to Subgroup I, and coincided with the sexual isolates of Valsa sordida from GenBank, which verified the consistence between asexual Cytospora chrysosperma and sexual Valsa sordida. On the other hand, the phylogeny tree also shows Cytospora chrsosperma isolates in China are more homogenous with isolates in America and Iran than those in UK. The relationships between C. chrysosperma and C. mandshuria, C. ambiens and C. mandshuria are not clear in this paper, and ITS sequences are not enough to distinguish them if there is no other gene's assistance.