Taxonomic And Phylogenetic Studies Of A Rust Genus Chrysomyxa In China

Biotrophic rust fungi of the genus Chrysomyxa are widespread in the northern hemisphere where they cause witches' brooms and needle and cone diseases,mainly on Picea,Tsuga and Keteleeria.Chrysomyxa rusts are responsible for significant economic losses,especially in spruce plantations.The traditional identifications of the rust genus,which is based on host specificity and spore morphology,leave many open questions.To better understand the taxonomy and phylogenetic relationship of Chrysomyxa in China,it is necessary to reveal the interspecific taxonomy and phylogenetic relationship through the combination of morphology and molecular phylogeny,and to establish a reliable taxonomy system.In our study,a total of 364 specimens from China were included,and light and scanning electron microscopy and genomics approaches were used to determine the taxonomic status of the rust genus and the patterns of evolution as well as host specialization.The phylogenetic trees constructed from 28S and the ITS have revealed the relationship between Chrysomyxa,Diaphanopellis and Caeoma species and the relationship between Chrysomyxa,Diaphanopellis and Caeoma.Main results are as follows:1.The valid names of 15 Chrysomyxa species in China are given,together with synmonyms,new descriptions for each spore stages,revised descriptions,specimens examined,distribution and the classification table of Chrysomyxa species are also listed.The morphological characteristics and molecular phylogenetic studies of 15 Chrysomyxa species distributed in China were studied systematically for the first time.2.The surface structure of aeciospores and urediniospores have been proved to be more reliable and accurate taxonomic characters for the delimitation of Chrysomyxa species.Furthermore,the aeciospore-surface structures of 15 Chrysomyxa species were classified into ten types based on gross shape and size of processes on the spore surface,and they were categorized into four major types:echinulate,annulate,verrucose and nailheaded,in particular,the annulate type was further classified into seven subtypes(A1-A7)on the basis of the shape of processes.The urediniospore-surface structures were classified into three major types:coronate,annulate,and verrucose.3.The relationship between Chrysomyxa and Caeoma was discussed,and the aecial stage of Caeoma yunnanensis was firstly described.This study was undertaken to infer the taxonomic placement of Caeoma species and to clarify their phylogenetic affinities to Chrysomyxa species using molecular data,and to determine reliable morphological characters as taxonomic criteria for the separation of these genera.4.Chinese specimens collected on needles of P.wilsonii were morphologically identified and proved to be the aecial stage of Chrysomyxa succinea by molecular phylogenetic analysis for the first time.Based on aeciospores and aecial perdium morphology,and the two rust fungi on P.asperata were identified as two new Chrysomyxa species,Chrysomyxa diebuensis C.J.You&J.Cao and Chrysomyxa zhuoniensis C.J.You&J.Cao.5.The molecular phylogenetic relationship of Chrysomyxa based on 28S and ITS regions was established.The relationship between phylogenetic groups and morphological clades showed that the aeciospore surface-structure and urediniospore surface-structure are reliable taxonomic characters.