Taxonomic And Phylogenetic Analysis Of Criconematoidea From China

Criconematoidea were a class of parasitic nematodes with ring-type esophagus,extra-root parasitism(a few semi-parasitic)plants,with a particularly wide range of hosts,mainly living around the roots of crops and woody plants.Criconematoidea cause some degree of damage to the root system of the host plants with their strong style,providing an infection site for other pathogenic microorganisms,causing complex infestations to the plant,resulting in certain economic damage.The traditional subfamily nematodes of Criconematoidea were mainly classified according to the epidermal characteristics of nematodes,and their classification systems have become more complex with the intervention of molecular identification methods.At the same time,there is still great potential for excavation in the identification of Criconematoidea species in China,and it is of great significance to conduct systematic research on Criconematoidea to clarify their geographical distribution and evolutionary relationship.We collected soil samples around various plant roots nationwide,and the Criconematoidea identification methods mainly based on morphological,and molecular biology identification was used as an auxiliary means.The main experimental results were as follows:1.Species identification and geographical distribution of Criconematoidea: 1057 samples were collected and separated from the soil around the roots of various plants nationwide from2019 to 2022.Combined with this study,the divergence between the species of Criconematoidea has been found in China.Also,the dominant species were different in various areas.In the south of China,the dominant genera of Criconematoidea were Hemicriconemoides,Discocriconemella and Hemicycliophora;the domi-nant genera of Criconematoidea in northern China were Criconemoides and Mesocriconema;Among them,conifer was the most common in maize rhizosphere soil and wheat rhizosphere soil;ring and groove ring were mainly common in areas with high altitude and large temperature difference in China.In the northern part of our country,Criconemoides informis,C.parainformis,C.geraerti,were common species.In the course of the experiment,the optimal method for making high-quality permanent slices of Criconematoidea was summarized.2.A total of 25 species of Criconematoidea were identified based on morphological and biochemical features exist.They were 2 species of Criconema,1 species of Ogma,1 species of Discocriconemella,4 species of Mesocriconema,6 species of Criconemoides,7 species of Hemicriconemoides,2 species of Gracilacus,and 2 species of Paratylenchus.Among them,two newly recorded species,Criconema petasum and Hemicriconemoides phoenicis,were found in Xinyang,Henan Province and Hangzhou,Zhejiang Province,respectively.3.Hylogenetic analysis of Criconematoidea: The gene sequences of 15 Criconematoidea were amplified based on18 S r DNA,ITS r DNA,and 28 S r DNA,and compared with the reference gene sequences in the Gen Bank database.The preliminary studies of phylogeny had been carried out.Gene sequence alignment analysis clarified that the genus Criconemoides was a paraphyletic taxa,and the genus Hemicriconemoides was a monophyletic taxa;the genus Paratylenchus and the genus Gracilacus belong to the family Tylenchulidae,and the genus Ogma,the genus Discocriconemella and the genus Hemicriconemoides belong to the family Ciconematinae.The classification was a relatively independent genetic evolution relationship;the classification of the genus based on morphological characteristics was confusing,and further research was needed.The 18 S r DNA gene sequences were used to analyze the genetic evolution of three common species in northern of our country.It was found that C.geraerti did not have intraspecific genetic differences in different regions;the nematode C.informis has great intraspecific gene differences in different regions.After accurate species identification by morphological identification,the gene sequences of 15 species of Criconematoidea were obtained by molecular identification and other methods.The gene sequence data of Ogma serratum,Mesocriconema ornatum,C.annulatus,and 12 other ring nematodes were obtained for the first time in our country,by means of morphological and biochemical identification.These sequences had been submitted to the Genbank database,will probably feed research on comparative genomics of Criconematoidea.This will also help to design new molecular markers for the identification or characterization of Criconematoidea.