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.