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Lance nematodes (Hoplolaimus spp.) feed on the roots of various plants, including key horticultural products. An investigation of the genetic diversity and structure of six Hoplolaimus species, utilizing the cytochrome c oxidase I (COI) of the mtDNA gene, was based on 174 sequences available on the NCBI. Based on the COI of mtDNA, the haplotype analysis revealed 44 haplotypes. Nucleotide diversity was low among all species of Hoplolaimus, except for H. magnistylus (π = 0.04915) and H. stephanus (π = 0.06746). In contrast, haplotype diversity (Hd) was high, especially for H. stephanus (Hd = 0.89) and H. pararobustus (Hd = 0.90). Phylogenetic analysis grouped the various populations into eight clades, and the result showed that H. magnistylus was placed in three different clades, which showed high variability in haplotype supported by the haplotype network. Neutrality tests and mismatch distribution based on the mtDNA supported the hypothesis of a constant population with no expansion in Hoplolaimus, except for H. concaudajuvencus (Tajima (D) = −0.84971) and H. columbus (Tajima (D) = −0.87674). In conclusion, genetic analysis showed a neutral evolution amongst the Hoplolaimus species. The result of the present study provides a better insight into the Hoplolaimus species toward species delimitation and managing this plant-parasitic nematode in various crops.

Lance nematodes (Hoplolaimus spp.) feed on the roots of a wide range of plants, some of which are agronomic crops. Morphometric values of amphimictic lance nematode species overlap considerably, and useful morphological characters for their discrimination require high magnification and significant diagnostic time. Given their morphological similarity, these Hoplolaimus species provide an interesting model to investigate hidden diversity in crop agroecosystems. In this scenario, H. galeatus may have been over‐reported and the related species that are morphologically similar could be more widespread in the United States that has been recognized thus far. The main objectives of this study were to delimit Hoplolaimus galeatus and morphologically similar species using morphology, phylogeny, and a barcoding approach, and to estimate the genetic diversity and population structure of the species found. Molecular analyses were performed using sequences of the cytochrome c oxidase subunit 1 (Cox1) and the internal transcribed spacer (ITS1) on 23 populations. Four morphospecies were identified: H. galeatus, H. magnistylus, H. concaudajuvencus, and H. stephanus, along with a currently undescribed species. Pronounced genetic structure correlated with geographic origin was found for all species, except for H. galeatus. Hoplolaimus galeatus also exhibited low genetic diversity and the shortest genetic distances among populations. In contrast, H. stephanus, the species with the fewest reports from agricultural soils, was the most common and diverse species found. Results of this project may lead to better delimitation of lance nematode species in the United States by contributing to the understanding the diversity within this group. The main objectives of this study were to delimit Hoplolaimus galeatus and morphologically similar species by using morphology, phylogeny and a barcoding approach, and to estimate the genetic diversity and population structure of the species found. Four morphospecies were identified: H. galeatus, H. magnistylus, H. concaudajuvencus, and H. stephanus along with a currently undescribed species. Pronounced genetic structure correlated with geographical origin was found for all species, except for H. galeatus. H. stephanus, the species with the fewest reports from agricultural soils, was the most common and diverse species found.