Identification Of Tylenchidae Species Based On Morphology And Phylogenetic Analysis Using COI Gene

Nematodes in the Tylenchidae family are abundant and diverse in soil fauna,and are of great importance in soil ecological processes.Compared to other plant parasites,the taxonomy in Tylenchidae is problematic for their small size with a low observational resolution and lack of DNA sequences of most described speices.In this study,several species of Tylenchidae were identified based on morphologica and molecular characterics.Mitochondrial Cytochrome Oxidase subunit I(COI)gene of the nematodes have been sequenced and be used to evaluate the potential of COI sequences for identification of Tylenchidae species and phylogenetic analyses.1.Identification of six records of Tylenchidae: Six species belonged to six genus of Tylenchidae were identified including Tylenchus arcuatus,Malenchus bryanti,Coslenchus costatus,Lelenchus leptosome,Filenchus vulgaris,Aglenchus muktii.Based on light morphology,scanning-electron microphology and molecular characteristics.T.arcuatus,M.bryanti were first reported in China.More detailed morphologys have been recovered,and molecular date were obtained by sequencing r RNA-18S、28S D2-D3,COI genes.2.Mitochondrial COI gene is valid to delimitate Tylenchidae(Nematoda: Tylenchomorpha)species: Mitochondrial Cytochrome Oxidase I(COI)gene is an important barcoding gene that has been widely used species identifications and phylogenetic analyses.However,currently COI data in Gen Bank is only available for one species(Lenlenchus brevislitus)in Tylenchidae.To evaluate the validation and robustness of COI phylogeny in comparison to well-established r RNA phylogeny,we newly obtained 27 COI sequences from 12 species belong to Tylenchidae and newly sequenced corresponding 28 S and 18 S r RNA of analyzed Tylenchidae species.The analysis of genetic distance of the species suggested that most species can be well-separated except for two reciprocally similar genera Aglenchus and Coslenchus.Our results concur with previous studies that both regions of 28 S and 18 S r RNA showed serious limitations: phylogenies are poorly resolved and support values do not agree with each other.The results suggest that COI gene is valid to delimitate Tylenchidae species but the fail to resolve phylogenetic relationships.3.Intra-specific variations of Lelenchus leptosome or cryptic species:In the study,we recovered two populations of Lelenchus leptosoma that similar in morphology(including SEM)only with minor morphological variations,but significantly divergent in phylogenetic placements.The results showed that the extremely small size masks the actual morphological difference in nematodes.The results showed that there may be one cryptic species in Lelenchus leptosome two populations.