Morphological and molecular analyses of three populations of Meloidoderita whittoni (Sledge & Christie, ) comb. n. (syn. Sphaeronemawhittoni; Tumiotawhittoni) 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.
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.
Two populations of needle nematode, Longidorus longicaudatus Siddiqi, 1962, are described from Quercus hemisphaerica, Q. nigra and Q. virginiana from north Florida, USA. These populations are characterised morphologically by females having a body shorter than 3800 μm, a rounded or slightly flattened lip region, an amphidial fovea pouch-like often with two symmetrical lobes, an odontostyle 99-110 μm long, a conoid tail ending in a bluntly pointed terminus, ranging values of ratio c′ greater than 2, and males very rare. The polytomous code for these populations is A34, B23, C2, D23, E2, F12, G12, H6, I12, J1, K6. Although the morphology and morphometrics of these two populations fit the original description of Longidorus longicaudatus, Florida specimens have greater diameters of lip region, mid and anal body than those of the five type specimens used for the description of this species. The Florida L. longicaudatus is similar to L. paralongicaudatus, but differs from the paratypes of this species in having smaller and greater values of ratios c (53.8 (43.8-64.5) vs 79.2 (61.9-103.5)) and c′ (2.4 (2.1-2.9) vs 1.8 (1.5-2.0)), respectively, and longer tail (60 (53-67) vs 46 (36-53) μm). Molecular characterisation of one of the two Florida L. longicaudatus populations was made based on the D2-D3 of 28S rRNA, ITS1 rRNA and COI gene sequences. The results of the ITS1 rRNA gene sequence analysis indicated that it is genetically different from L. paralongicaudatus. A few specimens of a needle nematode associated with L. longicaudatus were identified morphologically and molecularly as the pine needle nematode, L. americanus. This detection is a new record of the occurrence of the pine needle nematode in Florida.
Hemicaloosia vagisclera n. sp. is described from Bermuda grass (Cynodon dactylon) in Florida. This new species is characterised by females with body slightly ventrally arcuate in death, face with a prominent elliptical oral disc, large amphids, slender stylet with mean length 64 μm, lateral field consisting of a single longitudinal line marked by continuous and discontinuous transverse striae, oval and full spermatheca, sclerotised vaginavera and tail annuli width greater than that of remaining body annuli. Diagnostic characters for the males are a C-shaped body, head with 4-5 faint lip annuli and pronounced oval oral disc, lateral field with two longitudinal lines intersected by transverse striae, tail digitate in the distal portion posterior to bursa, distinctly annulated and with a round terminus. Molecular characterisation of H. vagisclera n. sp. using the D2-D3 domain of 28S rRNA, partial 18S rRNA and ITS rRNA gene sequences is also provided. The phylogenetic relationships of this species with other representatives of the suborder Criconematina are presented and indicate that H. vagisclera n. sp. has sister relationships with Caloosia longicaudata supporting the classification of Caloosia together with Hemicaloosia as separate genera in the family Caloosiidae. A diagnostic PCR-ITS-RFLP profile for H. vagisclera n. sp. is also given together with an identification key for seven known species of Hemicaloosia.
The cystoid sedentary nematodes of the Heteroderidae include more than 30 recognised species belonging to from nine to 11 genera, depending on the opinion of the authority. In the present study, we collected nematode populations of species belonging to some of these genera, as well as other cyst-forming species from different locations in the USA, Vietnam, Germany and Russia. The populations of cystoid nematodes represent seven valid species, Atalodera carolynae, Cryphodera sinensis, Meloidodera astonei, M. floridensis, M. mexicana, M. sikhotealiniensis, Rhizonemella sequoiae, two unidentified species of Atalodera, six unidentified species of Cryphodera, and three putative new species of Rhizonemella. We also obtained samples of cyst-forming nematodes that include an unidentified species of Betulodera from California, and Heterodera guangdongensis from Vietnam. A population of Rotylenchulus sp. from Arizona, intercepted in Florida, and a population of an unidentified species of Verutus from Germany were also added to this study. All of these populations were characterised using sequences of the D2-D3 of 28S rRNA, ITS rRNA or mitochondrial COI genes. A total of 89 new sequences were obtained from these analyses. Phylogenetic relationships within the family Heteroderidae were reconstructed based on the D2-D3 of 28S rRNA, ITS rRNA and mitochondrial COI gene sequences. Results revealed that the subfamily Ataloderinae was paraphyletic. Ekphymatodera thomasoni, a non-cyst-forming species, clustered with the cyst-forming nematodes. Representatives of the subfamily Verutinae formed clades within Heteroderidae. The genus Meloidodera was non-monophyletic and distributed within two clades: i) M. sikhotealiniensis and Cryphodera spp. from Asia and Europe; and ii) M. astonei, M. floridensis and M. mexicana from North America. Based on comparative molecular analysis Meloidodera alni syn. n. is proposed as a junior synonym of M. sikhotealiniensis. Problems of taxonomy and phylogeography of cystoid nematodes are also discussed.
Morphological identification of spiral nematodes of the genus Helicotylenchus is a difficult task because most characters used for their diagnosis vary within species. In this paper we provide morphological and molecular characterisations of several spiral nematodes, H. broadbalkiensis, H. digonicus, H. dihystera, H. microlobus, H. paxilli and H. pseudorobustus, collected in different geographical areas of USA, Switzerland, Italy, New Zealand, Spain, UK, South Korea and Russia. We suggest that H. microlobus and H. pseudorobustus are valid species separated from each other morphologically and molecularly. Seven species with distinct molecular characteristics are also distinguished, but are not ascribed morphologically to any specific taxon because of the low number of specimens available. Phylogenetic relationships of H. pseudorobustus with other Helicotylenchus species are given as inferred from the analyses of 154 sequences of the D2-D3 of 28S rRNA gene and 37 sequences of ITS rRNA gene.
The stubby root nematodes are world-wide distributed polyphagous root ectoparasites and can cause damage to a wide range of crops and natural vegetation. In this study, 22 valid and putative species of stubby root nematodes were identified in 37 samples collected in Malaysia, Mexico, Russia, and the USA (California, Florida, Minnesota and Nevada). The analysis of 58 new sequences of the D2-D3 expansion fragments of 28S rRNA gene revealed the following species: Nanidorus minor from California, Florida and Mexico, N. renifer from Florida, two unidentified Nanidorus species from California and Malaysia, respectively, Paratrichodorus allius from Florida and Minnesota, P. pachydermus and Paratrichodorus sp. from Russia, Trichodorus californicus, T. intermedius, and T. obscurus from California, T. obtusus from Florida, eight unidentified Trichodorus species from California, one unidentified Trichodorus species from Nevada, and two unidentified species of stubby root nematodes, one of Trichodorus and another undetermined species from Mexico. Molecular characterisation of T. californicus, T. intermedius and T. obscurus is given for the first time. The phylogenetic tree reconstructed from the analysis of 108 D2-D3 of 28S rRNA gene sequences of 58 valid and putative species of the stubby root nematodes contained five major clades: i) Trichodorus from Europe, Asia and North America; ii) Nanidorus and Trichodorus from Asia; iii) Trichodorus from California; iv) Paratrichodorus from several distant geographical regions; and v) Monotrichodorus from Central and South America. It has been hypothesised that the California Floristic Province is one of the centres of origin and diversification of stubby root nematodes. There is no information on the economic importance of the stubby root nematode species found in California and Mexico. The confirmation of the occurrence of N. renifer and P. allius in Florida should be of concern for the blueberry and potato industries in the state.
Phylogenetic analysis of five gene fragments: ITS-rRNA, D2 and D3 of 28S
rRNA, 18S rRNA, Hsp90 and actin, of Heterodera species and two
representative Afenestrata species, A. koreana and A. orientalis, form a
clade with H. cynodontis, H. bifenestra and an unidentified Heterodera sp.
infecting grasses. Based on these results and the consideration that the key
diagnostic characters of Afenestrata are convergent and do not define a
clade, synonymisation of Afenestrata with Heterodera is proposed. The
following new combinations are made: H. africana comb. n., H. axonopi comb.
n., H. koreana comb. n., and H. orientalis comb. n. Furthermore, H. (=
Afenestrata) sacchari is renamed as H. saccharophila nom. nov. to avoid
homonymy. All these species, together with H. bamboosi, are regarded as
members of a paraphyletic ‘Afenestrata group’ within Heterodera. Whilst
recognised as artificial, the Afenestrata group is nevertheless an aid to
discussion about these similar species. Morphological and molecular
characterisation of populations of H. koreana comb. n. from Florida and H.
orientalis comb. n. from Florida and Guatemala verify the identification of
these populations as valid representatives for molecular studies of the
species. Light and SEM observations also provide new detail and a broader
understanding of the morphological range of both species. These include a
longer stylet for females of H. koreana comb. n. and H. orientalis comb. n.
than reported in the original descriptions. In addition, previously
unreported tuberculate ridges are noted on the surface of vulval lips of H.
orientalis comb. n. The lip region of second-stage juveniles of H. koreana
comb. n. and H. orientalis comb. n. both include fused adjacent submedian
lips that also fuse with the labial disc and the second lip annulus. The
ITS-rRNA gene sequences of H. orientalis comb. n. populations from Florida
and Guatemala were similar to those from the Russian type locality.
Diagnostic PCR-RFLP of ITS-rRNA profiles with six enzymes for H. orientalis
comb. n. and H. koreana comb. n. are given. A key for the morphological
identification of species of the Afenestrata group is provided.