Characterisation of some Scutellonema species (Tylenchida: Hoplolaimidae) occurring in Botswana, South Africa, Costa Rica and the USA, with description of S. clavicaudatum sp. n. and a molecular phylogeny of the genus

Abstract

The genus Scutellonema contains more than 40 species of spiral nematodes with enlarged phasmids called scutella. In this study, we provide morphological and molecular characterisation of S. clavicaudatum sp. n., S. brachyurus, S. bradys, S. cavenessi, S. transvaalense, S. truncatum and Scutellonema sp. A. from North and Central America, and Africa. The new species, S. clavicaudatum sp. n., was found on sugarcane in South Africa and is characterised by a lack of lip annuli as in S. africanum, S. siamense and S. truncatum. The lip region, in both males and females, is conical and marked by six large rectangular blocks separated or fused with the submedian and lateral lip sectors, which surround a round and distinct labial disc. Females of this new species also have large vaginal glands, a functional spermatheca, the lateral field posterior to the scutellum ending in a bluntly pointed shape and a clavate tail. Morphological descriptions, measurements, light and scanning electron microscopic photos and drawings are also given for S. bradys, S. cavenessi, S. transvaalense and S. truncatum. The study of spiral nematode samples from Florida, USA, confirmed the presence of a morphologically and genetically atypical populations of S. bradys. The morphology of the S. bradys population from Bermuda grass in pasture land from central Florida fits that of type specimens of this species, but differs in having a truncate tail terminus rather than round and also a prominent spermatheca filled with flagellate spermatozoa. Other Florida Scutellonema samples analysed in this study belonged to S. cavenessi, a species native to West Africa. This is the first report of S. cavenessi in Florida, where it parasitises the ornamental plant Sansevieria trifasciata. Our study showed a high level of intraspecific variation for Scutellonema rRNA and mtDNA genes, which can reach 5.6% for the D2-D3 of 28S rRNA, 12.9% for the ITS rRNA genes and 14.4% for the COI gene. Phylogenetic relationships within Scutellonema are given as inferred from the analyses of the D2-D3 of 28S rRNA, ITS rRNA and the COI mtDNA gene sequences