Morphological and Molecular Characterization of Hoplolaimus tuberosus n. sp. (Nematoda: Hoplolaimidae) Associated with Potato in Uganda

The new nematode species Hoplolaimus tuberosus n. sp., isolated from potato rhizosphere in Budwale sub-county, Mbale district, Eastern Uganda, is characterized based on light and scanning electron microscopy alongside four molecular markers. Females of H. tuberosus n. sp. are moderately large (1.2–1.6 mm) and exhibit distinctive morphological features, including an offset lip region with 4–5 lip annuli, a basal lip annule divided into 10–12 irregular blocks, a robust stylet (45–50 μm), a variable lateral field, characterized by one incisure (zigzag longitudinal line formed by anastomoses) anteriorly and posteriorly, and 2–3 irregular, incomplete striae at mid-body, a secretory-excretory pore positioned anterior to the hemizonid, 6 gland nuclei, and a hemispherical to bluntly rounded tail with 8–10 annuli. Males are slightly smaller at 1.0–1.3 mm, have a basal lip annule divided into 2–4 blocks and relatively long spicules (46–58 μm). Phylogenetic analyses of COI mtDNA, ITS-rRNA, 18S-rRNA and D2D3 of 28S-rRNA demonstrated a close relation of the new species with morphologically similar species (Hoplolaimus columbus, Hoplolaimus indicus, Hoplolaimus seinhorsti, Hoplolaimus dubius and Hoplolaimus pararobustus) yet H. tuberosus n. sp. had in all analyses a distinct phylogenetic position. The population density of 50–75 H. tuberosus n. sp. per 100 ml of soil, combined with the polyphagous nature of related Hoplolaimus species, suggests that this new species could pose a significant pest threat to potato crops, warranting further pathogenicity studies.