Morphological and molecular characters of two Helicotylenchus species from South Africa and relationship of selected soil parameters with H. pseudorobustus

During a survey of plant-parasitic nematodes in South Africa's Limpopo Province, two species of Helicotylenchus were identified, namely H. dihystera and H. pseudorobustus. The morphological and molecular characteristics of these species were found to be consistent with those of the known species. A phylogenetic analysis of Helicotylenchus populations based on 28S rDNA was conducted, and it was found that the H. dihystera identified in this study belonged to the same group as other H. dihystera specimens with a 1.00 posterior probability support. Moreover, phylogenetic analysis of H. pseudorobustus based on 18S rDNA placed the test population close to other H. pseudorobustus specimens with 0.97 posterior probability. Scanning electron microscopy (SEM) for Helicotylenchus species also revealed noticeable dissimilarities in the labial disc and lateral field of the tail region between the two species from the present study, including H. pseudorobustus, and H. dihystera. The redundancy analysis (RDA) showed that H. pseudorobustus had a correlation with pH and clay of the soil. In conclusion, despite the challenges associated with identifying Helicotylenchus species, SEM and rDNA markers can be considered as highly effective tools to distinguish the species correctly and accurately.