Meloidoderita whittoni (Sledge & Christie, 1962) comb. n. (Tylenchida: Sphaeronematidae) and its parasitic habits on sweet gum (Liquidambar styraciflua L.)

Abstract

Morphological and molecular analyses of three populations of Meloidoderita whittoni (Sledge & Christie, 1962) comb. n. (syn. Sphaeronema whittoni; Tumiota whittoni) collected in Florida from sweet gum (Liquidambar styraciflua L.) indicated that this species is a representative of Meloidoderita rather than Sphaeronema, where it was included in the original description, or Tumiota, to where it was subsequently transferred. However, this species can be considered an atypical representative of the genus, because it differs from the other species of this genus in having females retaining the eggs inside a thin-walled uterus, which remains encased inside their body. After egg deposition inside the uterus, the female dies and its body is transformed into a persistent tanned sac with a thick cuticle, devoid of ornamentations, which protects the eggs like a heteroderid cyst. The female secretes from the vulva a gelatinous matrix, which becomes hardened in time and encases its body for protection against predation and parasitism by biological antagonists as has been suggested for other tylenchuloid nematodes. No egg deposition outside the female body was observed. Second-stage juveniles of this species have a semi-endoparasitic, rather than endoparasitic, habit as in other known Meloidoderita species. This is the first report of a sphaeronematid having a cyst stage fitting the definition of a heteroderid cyst. Phylogenetic relationships between some species of Tylenchuloidea and Criconematina are analysed using the partial 18S rRNA, the D2-D3 of 28S rRNA and the ITS rRNA gene sequences.