Six species belonging to the Criconematina, including a morphologically cryptic population within the Mesocriconema curvatum-group, are characterised based on integrative taxonomy based on morphological and molecular phylogenetic inferences from analyses of the 28S-rRNA, ITS-rRNA and COI gene sequences. Mesocriconema sp. 1 is morphologically similar to M. nebraskense and M. curvatum, differing from M. curvatum by the occasional presence of 1-2 anastomoses and a relatively higher R value, and from M. nebraskense by only a narrowed first lip annulus. However, based on COI gene sequence analysis, significant differences among the three species are evident. The sequence information in the COI gene among Mesocriconema spp. continues to reveal the existence of cryptic species within well-established species designations, and the concept of Molecular Operational Taxonomic Units might be helpful in grouping the different lineages according to sequence identities. Mesocriconema nebraskense is detailed herein for the first time outside the USA. DNA sequences of Hemicycliophora labiata were similar to those in GenBank while the existence in Korea of M. curvatum, Hemicriconemoides brachyurus and Paratylenchus nanus is molecularly confirmed.
Natural volatiles released by the fungus, Annulohypoxylon sp. FPYF3050, were evaluated against the pine wood nematode (PWN), Bursaphelenchus xylophilus. Our results showed that volatile organic compounds (VOCs) caused 64.1 and 58.4% mortality of second-stage juveniles (J2) and mixed-stages (eggs, J2, third- and fourth-stage juveniles, and adults) of populations of PWN, but no inhibitive effects were detected on nematode eggs in the experiment. Analysis of the gases within the Petri plate by gas chromatography-mass spectrometry (GC-MS) showed a yield of an unique volatile with dominant 1,8-cineole in 77.4% relative area (RA) after 72 h treatment of nematodes with Annulohypoxylon sp. FPYF3050 and Botrytis cinerea. The commercial 1,8-cineole at concentrations of 2, 5, 10 and 15 μl ml−1 was applied to examine nematicidal activity. The results showed that 1,8-cineole had a 40-100% inhibition on the nematode eggs during 48 h treatment, more than 82.9% mortality of J2 after 24 h, 48 h and 96 h, and 18.7-91.9% mortality of the mixed-stage population, depending on the period after exposure. This result indicates that 1,8-cineole in the volatile gas emissions of Annulohypoxylon sp. FPYF3050 may play a crucial inhibitory effect on the pine wood nematode The nematicidal volatile gas from fungi may provide a useful biocontrol agent for controlling B. xylophilus.
The ultrastructural morphology of the buccal capsule and intestine (mid-gut) of the predatory marine nematode Sphaerolaimus balticus is investigated. The major part of the voluminous barrel-shaped buccal capsule is made up of strongly modified somatic cuticle and hence presents itself as an intricately differentiated cheilostome. The latter consists of three compartments: i.e., i) labial region; ii) striated region with six rows of fine longitudinal ribs; and iii) shagreen band penetrated by about ten projections of arcade tissue. The gymnostome and telostome are narrow and together constitute a small posterior portion of the buccal capsule. The mouth is evidently opened by contraction of anterior longitudinal somatic muscles. The intestine is characterised by a very thin and homogenous basal lamina. The cytoplasm of the enterocytes contains lipid granules, large electron-light vacuoles and rounded concentric inclusions in membranous vacuoles. Apical microvilli are separated from the lumen by a dense three-layered glycocalyx resembling the peritrophic membrane in the intestine of arthropods. The glycocalyx is only a supportive structure of the mid-gut. The most peculiar features of the intestine are the particularly strong junctions connecting the glycocalyx with the cells. The junctions appear as cytoplasmic bundles attached to the dense glycocalyx layer by dint of hemidesmosomes.
Globodera presently contains 13 valid and three as yet undescribed species. Three species, G. rostochiensis, G. pallida and G. ellingtonae, the potato cyst nematodes (PCN), cause significant economic losses on potatoes around the world. In our study we provide comprehensive phylogenetic analyses of 455 ITS rRNA, 219 COI and 164 cytb gene sequences of 11 valid and two undescribed species of Globodera using Bayesian inference, maximum likelihood and statistical parsimony. New 205 COI, 116 cytb and 21 ITS rRNA gene sequences were obtained from 148 populations of these species collected from 23 countries. The phylogenetic analysis revealed that Globodera displayed two main clades in the trees: i) Globodera from South and North America parasitising plants from Solanaceae; and ii) Globodera from Africa, Europe, Asia and New Zealand parasitising plants from Asteraceae and other families. Based on the results of phylogeographical analysis and age estimation of clades with a molecular clock approach, it is hypothesised that Globodera species originated and diversified from several centres of speciation located in mountain regions and then dispersed across the world from these regions during the Pleistocene. High genetic diversity of Bolivian populations of G. rostochiensis was observed for both mtDNA genes. Analysis of phylogenetic relationships of G. pallida and G. rostochiensis populations revealed incongruence in topology between networks inferred from mtDNA genes, which might be an indication of possible recombination and selective introgression events through gene flow between previously isolated populations. This puts some limitations on the use of the mtDNA marker as universal DNA barcoding identifier for PCN. Globodera bravoae syn. n. is proposed as a junior synonym of G. mexicana.
A new nematode species was recovered from the syconia of Ficus hirta var. roxburghii from Chaozhou, Guangdong, China. It is described herein as Ficophagus chaozhouensis n. sp. and is characterised by possessing the combined characters of a short post-uterine sac, excretory pore located near the head, amoeboid sperm, three pairs of subventral papillae on the male tail, rounded male tail tip with mucron (occasionally swollen), absence of gubernaculum (or apophysis), a blunt rosethorn-shaped spicule without a terminal cucullus, and a digitate rostrum with a broadly squared tip. Ficophagus chaozhouensis n. sp. was separated from other sequenced species by differences in the partial small subunit (SSU) rRNA gene and D2-D3 expansion segments of the large subunit (LSU) rRNA gene. Phylogenetic analysis with LSU D2-D3 expansion segment sequences suggested that F. chaozhouensis n. sp. is clustered in the same highly supported monophyletic clade with F. aculeata, F. maxima and F. yoponensis, and is sister to F. aculeata.
The rare genus and species Neometadorylaimus coomansi is characterised based on an abundant population found in West Bengal, India. New morphological and morphometric data are provided, together with SEM observations and the first description of its male. Molecular analyses (18S and 28S-rDNA sequences) were also done. A comparison of the present population with the two previously known ones, all from India, showed a remarkable variability in some features, especially the body length that ranges from 1.75 to 3.29 mm. The male is distinguished by its 1.83-2.06 mm long body, 54-55 μm long spicules, and nine or ten ventromedian supplements lacking an hiatus. New insights into the phylogeny of the genus are provided with an integrative approach combining morphological and molecular data. The monophyly of the Tylencholaimidae is supported, and a tentative relationship between Tylencholaimidae and other dorylaims lacking the pars refringens vaginae is suggested.
The plant-parasitic nematode, Paratylenchus bukowinensis, occurs ubiquitously in arable fields. Economic damage has been reported from, among others, cabbage, parsley, and celery, but other crops might be affected as well. Management of P. bukowinensis is difficult. Resistant cultivars are not available and chemical control is prohibited in most European countries. In addition, sustainable management is often hindered by a lack of information regarding the biology and host range of P. bukowinensis. To improve the management of P. bukowinensis in the future, a good understanding of the life cycle and host plant-nematode interactions is required. We investigated the host range, life cycle and natural decline of P. bukowinensis in five glasshouse experiments. A total of 26 plant genotypes comprising 22 plant species from eight plant families were studied. Plant species within the families Brassicaceae and Apiaceae were confirmed as good hosts, while plant species within the families Fabaceae, Asteraceae, Amaryllidaceae, Solanaceae, Amaranthaceae and Poaceae can be considered non-hosts or poor hosts. In roots of good hosts, P. bukowinensis completed its life cycle within 3-4 weeks. In the absence of a host plant, P. bukowinensis declined by 40% within the first 4 weeks, but then remained at this level until the experiment was terminated after 14 weeks. Overall, the host range of P. bukowinensis seems to be smaller than for other species within the genus Paratylenchus, such as P. projectus or P. similis. Control of P. bukowinensis using crop rotation should be feasible by rotating good hosts belonging to the families Brassicaceae and Apiaceae with non-hosts or poor hosts.
Two isolates of Steinernema bertusi n. sp. were separately recovered from Tito, Mpumalanga, and Port Edward, Kwa Zulu Natal, South Africa. In this paper, we describe the isolates as a new entomopathogenic nematode (EPN) species using molecular and morphological methodologies. The new species belongs to the cameroonense-clade, which consists of nematodes only isolated from the African continent. Steinernema bertusi n. sp. is characterised by having the longest infective juvenile (IJ) for this clade at 716 (628-814) μm. The IJ is further characterised by a body diam. of 32 (28-36) μm and the pattern for the arrangement of the lateral ridges from head to tail is 2, 4, 5, 4, 2. The first-generation male spicule and gubernaculum length is 82 (72-88) μm and 63 (54-72) μm, respectively. Only 25% of the second-generation males possess a mucron. The first-generation females of S. bertusi n. sp. have a slightly protruding vulva, with double-flapped epiptygmata and a mucron at the posterior end. The new EPN species is most closely related to S. sacchari and is the sixth species to be included in the cameroonense-clade.
Entomopathogenic nematodes (EPN) are excellent biological control agents possessing recycling ability as one of their major attributes. We report the presence of asymptomatic bacteria that can lead to disrupted or low progeny production in Heterorhabditis indica. In a one-to-one in vitro competitive bioassay with contaminants associated with H. indica cuticle, there was a significant suppression in the growth of Sphingomonas koreensis when stressed with the nematode symbiont Photorhabdus luminescens; however, P. luminescens was suppressed when sandwiched between Ochrobactrum anthropi. Bacillus bombysepticus associated with laboratory-reared Galleria when stressed by P. luminescens was significantly suppressed, but not so in the reverse assay. Both O. anthropi and B. bombysepticus were found to be insecticidal to Galleria larvae when fed orally. Tripartite interactive studies on the growth and multiplication of H. indica-P. luminescens symbionts in Galleria larvae, predisposed to S. koreensis, revealed no significant difference initially in the hermaphrodite formation, but subsequently there was a significant decline in the formation of amphimictic females and the final production of infective juveniles. In in vitro studies, none of the contaminants supported the growth and development of axenic H. indica. Adequate precautions should be taken to maintain proper hygiene to eliminate such contaminants while culturing the Galleria and EPN for use in the biological control of insects.
Hemicycliophora labiata was reported from the rhizosphere of Poa pratensis and for the first time in Korea. Females and juveniles are molecularly characterised and morphological and morphometric descriptions supplied. Species identification was made using an integrative approach considering morphological characteristics and the results of the analyses of the D2-D3 expansion segment of 28S rRNA, ITS1-5.8S-ITS2 of rRNA and the partial COI gene sequences. The phylogenetic position of H. labiata is resolved after recent misidentifications due to the existence of a wide morphological plasticity within the genus. Females and juveniles from Korea conform to the original description and also to subsequent species descriptions from Australia, South Africa, Sri Lanka, and India. Despite the close morphological similarities with H. typica de Man, 1921, the two species can be adequately differentiated based on molecular data. This is the first molecular characterisation of H. labiata. The use of molecular markers in species delimitation continues to explore the existence of species complexes, thus providing a better understanding of the unresolved species biodiversity within this speciose genus.