Summary

This study investigated the abundance, biomass, species richness, species distribution and feeding types of free-living nematodes in Lake Constance, a deep, oligotrophic lake in Germany. Three water depth zones, the sublittoral (13-30 m water depth), profundal (31-99 m) and deep profundal (100-250 m), were distinguished and 16 sites from each water depth zone were sampled. A high nematode species richness was determined at all three zones, with 129 species in the sublittoral, 113 in the profundal and 92 in the deep profundal. In total, 171 nematode species were identified in this study. The dominant species (relative abundance > 5%) in all water depths were Ethmolaimus pratensis, Eumonhystera filiformis, E. longicaudatula, E. vulgaris and E. andrassyi, Hofmaenneria brachystoma, Ironus tenuicaudatus, Monhystera paludicola/stagnalis, Prismatolaimus intermedius and Tobrilus gracilis. High mean densities of 507-730 indiv. 10 cm−2 were found at each water depth, with a mean overall density of 627 indiv. 10 cm−2. The high abundance resulted in a high mean biomass (1.19 mg wet weight 10 cm−2; range 0.92-1.37 mg wet weight 10 cm−2) for nematodes in Lake Constance. Deposit feeders were the dominant feeding type at all water depth zones (51.7%), followed by epistrate feeders (17.6%), chewers-omnivores (15.9%) and chewers-predators (11.0%). Suction feeders accounted for <4% in the lake as a whole. The structure of the nematode communities in the three zones correlated with sediment texture (water content, clay content), as well as total sulphur and nutrient-related parameters (ATP, bacteria, algae, C:N ratio).

In: Nematology

Summary

The cereal cyst nematode, Heterodera latipons, is an important plant parasite causing substantial yield losses in wheat throughout the world. This study aimed to determine genetic and pathogenic variation in H. latipons populations obtained from the southern part of Turkey. The populations were identified as H. latipons by sequencing the ITS-rDNA region and further sequence analysis showed an intraspecific genetic variation in H. latipons populations, which were clustered into different groups. The International Test Assortment materials were used to determine pathogenic variation (pathotypes) in these populations. The results showed that ‘Ortolan’, ‘Morocco’, ‘KVL191’, ‘Bajo Aragon 1-1’, ‘Herta’, ‘Martin 403-2’, ‘Sun II’ and ‘Pusa Hybrid Bsi’ cultivars were resistant or moderately resistant to the tested nematode populations. ‘Emir’, ‘Dalmatische’ and ‘Capa’ were susceptible to H. latipons populations. The Hatay population of H. latipons was detected as the most virulent nematode population because ten out of 20 cultivars were susceptible or moderately susceptible to this population. The least virulent population was the Kilis population, which caused susceptible reaction on six out of all cultivars with different levels. Based on this scheme, the Turkish populations were in the Ha1 group: the reactions of barley, oats and wheat classified them as either Ha41 or Ha51. Barley ‘KVL191’ was resistant to all nematode populations but susceptible to Ha51, and the reactions of the other barley cultivars were also consistent with the Turkish populations being Ha51. ‘AUS10894’ was susceptible to three nematode populations but resistant to Ha41, and the reaction of ‘Capa’ was also consistent with the Turkish populations being Ha51. However, the degree of susceptibility of all wheat differentials distinguishes the Turkish populations from other pathotypes in the Ha1 group.

In: Nematology

Summary

Whilst investigating plant-parasitic nematodes in Urmia City, West Azerbaijan, Iran, soil samples were collected from the rhizosphere of willow trees (Salix babylonica) known to have a population of cyst nematodes. Morphological, numerical and molecular approaches revealed that this population represented the willow cyst nematode, Heterodera salixophila, the first report of this species from Iran. Reproduction of the nematode on S. babylonica was confirmed by inoculating 5000 viable eggs and second-stage juveniles (J2) per kg soil on 2-year-old seedlings of S. babylonica grown in pots containing sterilised soil and incubated under glasshouse conditions. Principal Component Analysis (PCA) and hierarchical cluster analysis of morphometric characters of J2 and vulval plates of species within the Humuli group supported the separation of H. salixophila from other species in this group. In the ITS-rRNA phylogenetic tree, the Iranian population of H. salixophila formed a cluster with two other populations of the species from Belgium and Ukraine, while in the D2-D3 expansion segments of the 28S rRNA tree, it grouped with a population from Belgium as a basal clade in the Humuli group.

In: Nematology

Summary

Incorporation of castor bean cake into the soil results in the emission of four main compounds: skatole, γ-decalactone, 4-methylphenol and phenol. The toxic effects of these compounds on the life cycle of Meloidogyne incognita were studied here. Only phenol did not reduce hatching of M. incognita second-stage juveniles (J2) at any of the concentrations tested. The other compounds reduced J2 hatching by 42.1 to 59.3% at the highest concentrations. When J2 were immersed in Tween 80® solutions of each compound, at their respective LC50 values and inoculated into soil with tomato plants, reductions in the numbers of galls (48.5-69.3%) and eggs (42.8-62.5%) were observed in comparison with the control; this result was similar to that of carbofuran. The highest reductions in the numbers of galls (21.8-88.5%) and eggs (49.6-98.9%) occurred with all compounds when the highest concentration (500 mg l−1) was applied to the substrate at the moment of J2 inoculation. Volatile compounds of γ-decalactone and skatole failed to cause J2 immobility or mortality. However, phenol caused 95.8% and 4-methylphenol caused 100% mortality. With fumigation, the highest concentration (1000 mg (l substrate)−1) of any tested compound reduced gall numbers at a similar rate to the nematicide dazomet (98.7-100%) and reduced egg numbers (87.1-99.7%). The volatile compounds skatole, γ-decalactone, 4-methylphenol and phenol have a nematicidal effect on the life cycle of M. incognita and alter its pathogenic behaviour on the plant.

In: Nematology

Summary

Bursaphelenchus acaloleptae n. sp. is described and figured based upon its morphological characters and molecular profiles. The new species belongs to the xylophilus-group of the genus and is typologically characterised by its secretory-excretory pore being located slightly posterior to the median bulb, weakly tapering, relatively broad and straight female tail with variously shaped terminus, and rounded male bursal flap with squared terminus. The new species is phylogenetically and biologically closest to B. luxuriosae. These cryptic species share the host (habitat) tree species, Aralia elata (Araliaceae), the same carrier insect species, Acalolepta luxuriosa (Cerambycidae), and a characteristic phoretic adult form. However, the new species is typologically distinguished from all other xylophilus-group species by the combination of the above-mentioned characters and molecular profiles (SSU and LSU molecular barcodes). Further, B. acaloleptae n. sp. can be distinguished from its closest relative, B. luxuriosae, by mating experiments, i.e., these two species did not produce a viable F1 generation in reciprocal crossings, thereby confirming separate species status using the biological species concept.

In: Nematology

Summary

Based on earlier investigations, Bursaphelenchus sexdentati sensu lato consists of two distinct forms, a central European and a southern European type. In this paper we recognise these forms at species level and propose B. dietrichi sp. n. for the southern European type, regarding it as distinct from B. sexdentati sensu stricto. The relatively long (733-881 μm) and slender (a = 34.7-43.3) females of the new species have a small vulval flap, a long post-uterine sac extending for 46.6-75.3% of the vulva to anus distance, and a mostly conical tail with a more or less bluntly rounded terminus. The male spicules are strongly ventrally arcuate, measuring 13-17 μm along the arc, and have a bluntly pointed rostrum ca 2-3 μm long in the proximal part and a small cucullus at their distal end. The capitulum is slightly concave and the condylus is ca 2-3 μm long, truncated and slightly hooked. The oval bursa and the disposition of the male caudal papillae, as well as the presence of four lateral lines, justify the assignment of this taxon to the sexdentati-group. Bursaphelenchus dietrichi sp. n. can be distinguished from B. sexdentati s.s. and other related species by morphological characters and sequencing results. Bursaphelenchus sexdentati s.s. is also recorded from China for the first time.

In: Nematology
Author: Sergio Molinari

Summary

Plants have an immune system that can be exerted by every cell against a vast array of pathogens and parasites. This immune system has several levels of specialisation. A first level induces a general basal defence, after which specific pathogen-associated molecular patterns (PAMPs) are recognised by plant receptors. Normally, this basal defence is overcome by specialised pests by secreting specific effectors that suppress this first line of defence. Plant-parasitic nematodes have been found to secrete several such effectors through amphid and cuticle secretions or directly into the cells through their stylets. Many studies carried out on endoparasitic sedentary nematodes (ESN), in particular, reported the suppression of plant defence, especially in terms of down-regulation of the genes involved in salicylic acid (SA)-mediated defence, in the very first stages of plant-nematode interaction. However, plants can be immunised or primed against nematode attacks. Immunised plants respond to nematode infection more rapidly and efficiently and let a minor number of invasive juveniles become sedentary, develop to gravid females and reproduce. Immunisation of plants can be achieved by pre-treatments with chemicals that are functional analogues of the phytohormones that mediate defence reactions, such as salicylic acid (SA). Moreover, plants provided with the beneficial microorganisms commonly present in a healthy rhizosphere, such as arbuscular mycorrhizal fungi or opportunistic symbiotic fungi, have been found to be immunised against ESN. Immunisation is mainly mediated by up-regulation of SA-dependent defence genes, such as pathogenesis-related genes (PR-genes). Immunisation is systemic and can also work against herbivorous insects.

In: Nematology

Summary

Longidorus barsii sp. n., from Mt Tara in the Balkan Peninsula, is described and characterised by using a polyphasic approach. The species has numerous males. The female body is 5-7 mm long, rather stout and resembles a large Xiphinema. The lip region is wide, with rounded sides continuous with the neck, frontally flattened and depressed around the oral aperture, amphids are pouch-like and distinctly bi-lobed and the odontostyle is moderately long. The nuclei of the pharyngeal glands are in the normal position, the dorsal nucleus located somewhat posterior to anterior third of bulb. The uteri are long, the distal inner epithelium densely covered with papilla-like outgrowths. The tail is rounded, bluntly conoid and very short. Alpha-numerical identification codes: A4/5, B45, C3, D3, E2, F3, G 1(2), H1, I2, J1, K67. The morphologically most similar species are L. kheirii, L. polyae and L. profundorum. Additional observations are provided on the anterior body region and genital organs in L. barsii sp. n., L. piceicola, L. silvae, and L. uroshis. Selected features are discussed from the taxonomic and functional points of view. The D2-D3 expansion domains of the 28S rRNA gene and the ITS region of L. barsii sp. n. were amplified and sequenced. Phylogenetic analysis using the D2-D3 expansion domains of the 28S rRNA gene revealed close evolutionary relationships with L. polyae, L. athesinus and three unidentified Longidorus spp.

In: Nematology

Summary

Ektaphelenchoides shiroodensis n. sp. is described and illustrated based upon morphological, morphometric and molecular data. It was recovered from the bark samples of a dead alder tree (Alnus sp.) from countryside around Shirood city, Mazandaran province, in the north of Iran. The new species is characterised by 768-985 μm long females, its lip region separated from the body contour by constriction, lateral field with three barely visible lines, forming two weak bands, 26-29 μm long stylet with wide lumen without conophore and basal swellings, excretory pore always at the level with median bulb, post-vulval uterine sac (PUS) 43-76 μm long, elongate conoid posterior body region ending to a long filiform part with pointed tip, males common with dorsally convex conical tail ending to a short narrower region with pointed tip, seven precloacal + cloacal + caudal papillae and arcuate spicules with wide condylus, blunt rostrum and simple end. Based upon the similar posterior body region (‘tail’) and comparable PUS length, the new species was compared to three known species, viz., E. attenuata, E. hunti and E. pini. Comparisons with the aforementioned species and similar species under the genus Seinura are discussed. The phylogenetic affinities of the new species, based upon two partial small and large subunit ribosomal DNA (SSU and LSU rDNA D2-D3) sequences, are discussed. Furthermore, several ektaphelenchid and seinurid species previously described from Iran were recovered in the present study, sequenced for their aforementioned genomic markers, and included in the phylogenetic analyses.

In: Nematology