Morphological and molecular characterisation of Helicotylenchus zengchengensis n. sp. (Nematoda: Hoplolaimidae) from China, with a review on Helicotylenchus species in China

Abstract Helicotylenchus comprises a significant group of plant-parasitic nematodes that primarily feed on plant roots. This study focuses on the description of a newly discovered species, Helicotylenchus zenchengensis n. sp., from China. The distinguishing characteristic of this species, as observed under a microscope, is the absence of head annulation. The stylet, measuring between 23.8 and 29.3 μm, exhibits anteriorly flattened or indented stylet knobs. The elongated tail has a c value ranging from 15.8 to 22.6 and a c’ value between 1.9 and 2.4. It bears 15 to 18 tail annuli, presenting a conical shape with projections. The phasmids are located at the 4th to 10th body annulations posterior to the anus, while no males were observed. Three phylogenetic trees were constructed to determine the evolutionary relationships using the 18S rRNA, ITS, and 28S D2-D3 expansion segments of the newly discovered species and related Helicotylenchus sequences obtained from the database. Based on the ITS sequences, a phylogenetic tree revealed that H. zenchengensis n. sp. clustered with H. cuspicaudatus . However, it was distinguished from H. cuspicaudatus when examining the 18S and 28S rRNA sequences and morphological characteristics. Additionally, comprehensive and diagnostic tables for all known species of Helicotylenchus in China are provided for reference.