On the morphology and phylogeny of Robustodorus Andrássy, 2007 and two ‘Aphelenchoides’ species (Nematoda: Aphelenchoidinae)

Abstract

In a survey of nematode damage in groundnut ( Arachis hypogaea ) (Fabaceae) production areas in the Vaalharts Irrigation Scheme in the Northern Cape Province of South Africa, a nematode was recovered and initially believed to be a member of the genus Robustodorus , i.e. , the species has a characteristic robust stylet with very well-developed teardrop-shaped (garlic bulb-like) basal swellings. The specimens were recovered in large numbers from damaged hulls and kernels of field-collected groundnuts and, after thorough morphological and molecular studies, were subsequently identified as Aphelenchoides arachidis . Molecular analysis based on near-full-length small subunit (SSU), internal transcribed spacer (ITS) and D2-D3 expansion segments of the large subunit (LSU) rRNA genes supported the monophyly of A. arachidis , A. subtenuis and R. megadorus within the subfamily Aphelenchoidinae. Based on the typological characters observed in the present study compared with descriptions in the literature, these three species are considered as congeneric, i.e. , they share very well-developed basal swellings of the stylet. Accordingly, these two Aphelenchoides species are transferred to Robustodorus as R. arachidis n. comb. and R. subtenuis n. comb. In addition, the male tail characters of Robustodorus and Aphelenchoides are discussed