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Taisuke Ekino, Suguru E. Tanaka, Natsumi Kanzaki and Yuko Takeuchi-Kaneko

Summary

The virulence of Bursaphelenchus xylophilus, the pine wood nematode, varies greatly among different populations. Two inbred strains, called P3 and P9, were recently established via repeated full-sib mating. They exhibited remarkable differences in pathogenicity-related traits. Although their propagation did not differ when cultured on fungal lawns, P9 reproduced better in host seedlings and exhibited higher virulence. In the present study, we obtained fundamental information about P3 and P9 in terms of tolerance to oxidative stress and examined this tolerance and the cuticular ultrastructure. P9 survived better under hydrogen peroxide (H2O2)-stressed conditions than did P3. In addition, P9 had a thicker cuticle than P3. Although further studies are needed, these results suggest that the difference in tolerance in P3 and P9 was due not only to physiological features, such as H2O2-degrading ability, but also to physical factors (cuticle thickness).

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Cassandra Edmunds, Rory J. Post, Craig S. Wilding and Robbie Rae

Summary

Entomopathogenic nematodes (EPN) of the families Steinernematidae and Heterorhabditidae are lethal insect parasites that have been commercialised as biological control agents. EPN have been isolated from across the world but it has been more than 20 years since the last survey of the UK, and species like Steinernema carpocapsae have never been found here and positively identified through molecular biology. We collected 518 soil samples from a diverse range of habitats across the UK and baited them with Galleria mellonella to isolate EPN. Dead G. mellonella were placed in White traps and emergent EPN underwent DNA barcoding analyses. From the 518 samples, 3.5% were positive for EPN. No Heterorhabditis species were found, but seven isolates of S. glaseri, one isolate of S. feltiae, eight isolates of S. affine and two isolates of S. carpocapsae were found. This was the first confirmed record of S. carpocapsae in the UK.

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Kenta Uesugi, Masaaki Katsura, Naohiro Uwatoko, Yasushi Tateishi, Gaku Murata and Kei Iwabuchi

Summary

The suppressive effect of a black oat, Avena strigosa, breeding line KH1a on Meloidogyne spp. was examined in pot tests and on Meloidogyne incognita in pot and field tests. In pot tests, roots of black oats were examined 42-46 days after inoculation of 500 second-stage juveniles. There were significantly fewer egg masses on the roots of KH1a than on 12 black oat cultivars examined. KH1a was a poor host for four isolates of M. incognita, two isolates of M. arenaria and one isolate of M. javanica, and a non-host for one isolate of M. hapla. The effect of autumn and spring cropping of KH1a on soil nematode density was examined in M. incognita-infested fields. Nematode density after autumn cropping of KH1a was significantly lower than that after susceptible black oat, resulting in significantly lower P f/P i in KH1a (0.10 and 0.13) than in susceptible black oat (0.42 and 0.74). Damage indices of the succeeding crop, sweet potato, were significantly lower in KH1a plots than in susceptible black oat plots. In spring cropping, there were significantly fewer soil nematodes in KH1a plots than in susceptible black oat plots 3 weeks after cultivation. In both autumn and spring cropping, there was no significant difference in soil nematode density between KH1a and bare fallow. These results suggested that KH1a is a good alternative to current susceptible cultivars for the management of M. incognita.

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Ebrahim Shokoohi, Hadi Panahi, Hendrika Fourie and Joaquín Abolafia

Summary

A population of Macrolaimus arboreus was collected from the rhizosphere of pine in Iran. This population of M. arboreus is characterised by the body length, 800-1010 μm in females, lip region with six seta-like papillae directed anteriad, stoma nearly as long as wide (9-11 × 7 μm), with cheilostom slightly longer than gymnostom and cheilorhabdia and gymnorhabdia well-developed, pharyngeal corpus 1.8-2.0 times the isthmus length, with slightly swollen metacorpus, excretory pore located at isthmus level, female reproductive system monodelphic-prodelphic reflexed with short post-vulval uterine sac, female tail conical (57-67 μm, c = 13.7-15.0, c′ = 3.5-3.8), ending in an acute tip which is weakly curved dorsad, and phasmids at 54-60% of tail length. Measurements and illustrations, including SEM, are provided.

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Oleg Gorgadze, Elena Fanelli, Manana Lortkhipanidze, Alberto Troccoli, Medea Burjanadze, Estachio Tarasco and Francesca De Luca

Summary

A new species of entomopathogenic nematode, Steinernema borjomiense n. sp., was isolated from the body of the host insect, Oryctes nasicornis (Coleoptera: Scarabaeidae), in Georgia, in the territory of Borjomi-Kharagauli. Morphological characters indicate that the new species is closely related to species of the feltiae-group. The infective juveniles are characterised by the following morphological characters: body length of 879 (777-989) μm, distance between the head and excretory pore = 72 (62-80) μm, pharynx length = 132 (122-142) μm, tail length = 70 (60-80) μm, ratio a = 26.3 (23.0-29.3), H% = 45 (40-51), D% = 54 (47-59), E% = 102 (95-115), and lateral fields consisting of seven ridges (eight incisures) at mid-body. Steinernema borjomiense n. sp. was molecularly characterised by sequencing three ribosomal regions (the ITS, the D2-D3 expansion domains and the 18S rRNA gene) and the mitochondrial COI gene. Phylogenetic analyses revealed that S. borjomiense n. sp. differs from all other known species of Steinernema and is a member of the monticolum-group.

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Patrick M. Norshie, Ivan G. Grove and Matthew A. Back

Batch adsorption experiments were performed to determine the sorption of the nematicide fluensulfone as a technical-grade and a granular formulation (as Nimitz 15G) in six UK arable soils. The Freundlich and equilibrium sorption coefficients KF and KD, respectively, were generally low. KF and KD correlated positively with soil organic matter in all instances. The sorption kinetics was similar for both forms, but the KD was about four times lower for Nimitz 15G than the technical-grade, suggesting concentration dependency of fluensulfone sorption. The low sorption of fluensulfone across the soils indicates that partitioning of fluensulfone to the soil liquid phase may be unlimited. Therefore, substantial availability in the soil to be effective is likely. Sorption, therefore, may not limit fluensulfone efficacy. Nonetheless, these results call for cautious use of the nematicide because leaching is possible.

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Natsumi Kanzaki, Suguru E. Tanaka, Masaaki Ito, Koji Tanaka, Bernard Slippers and Masanobu Tabata

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Hugo H. Mejía-Madrid

Soil nematode abundance and MOTU diversity were estimated from a geographically broad area of Mexico that included four out of seven recognised vegetation types. Vegetation types were assessed for abundance and diversity of nematode communities and inferred ecological relationships between them. Soils were sampled from tropical rainforest, tropical dry deciduous forest, temperate coniferous forest and xerophytic shrub during 2013, 2014 and 2015. Fourteen sampling sites with ca 10-20 samples per site from 11 localities spread across Central Mexico were assessed. Altitudes sampled ranged from 113 m a.s.l. (tropical coastal plain) to 2400 m a.s.l. (Trans-Mexican Volcanic Belt). Samples were drawn from conserved and cultivated plots from each sampling site covering an area of ⩾100 m2. A total of 13 263 individuals from 25 identified families of nematodes were collected. Family abundance and complementarity indices between sites revealed to some extent the affinities between vegetation types. Nevertheless, statistical analyses revealed no differences between nematode family abundances between sites, only between families across all sites. Molecular operational taxonomic units (MOTU) methods were employed as a framework to assess biodiversity. From these, 77 high-quality sequences for taxonomic barcoding were recovered and later identified with morphological traits. Only six sequences matched at a 98-99% level with those reported in GenBank. Sequences amounted to a total of 41 MOTU, where 100% of the MOTU from both conserved and disturbed tropical rainforest, tropical dry deciduous forest and xerophytic shrub exhibited a ⩾3% cut-off genetic identity, whilst temperate coniferous forest and disturbed temperate coniferous forest showed 73% and 70% respectively. In addition, 12.2% MOTU were shared among localities and 87.8% exhibited an apparently locality-limited distribution. The potential for a considerable diversity of nematodes, as revealed from a small sample of MOTU diversity, is discussed.

Open Access

Yuuki Nakabayashi, Takuya Aikawa, Michinari Matsushita and Kazuhiko Hoshizaki

Summary

Detection of pine wood nematode, Bursaphelenchus xylophilus, is fundamental for effective control of pine wilt disease. Recent molecular techniques, such as DNA detection, have enhanced detectability of the nematodes whereas appropriate field sampling has received less attention. In order to elucidate a sampling design that most efficiently detects B. xylophilus using a commercially-distributed DNA detection kit, we compared detection levels of B. xylophilus using wood chips taken from various positions on dead trees. Results showed that the DNA kit had a higher detection level than the conventional method, and that trunk samples had higher levels than branch samples. Statistical model revealed that among-tree variation influenced the detectability more strongly than within-tree variation. Our results suggest that, in practice, with limited resources for control, it is more efficient to take samples from many trees with a minimum number from each tree, rather than taking many samples from a small number of trees.

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Ma. Teodora Nadong Cabasan, Arvind Kumar, Stéphane Bellafiore and Dirk De Waele

Summary

Five populations of Meloidogyne graminicola isolated from different rice-growing areas in the Philippines were characterised. The populations showed little phenotypic variability of second-stage juveniles and female perineal pattern. Differences in reproduction among M. graminicola populations were not observed on mature resistant Oryza glaberrima varieties ‘TOG5674’, ‘TOG5675’, ‘RAM131’ and ‘CG14’, or on susceptible O. sativa varieties ‘IR64’ and ‘UPLRi-5’. In all infected rice varieties, plant growth and yield-contributing traits showed no differences among the populations. A search on M. graminicola populations from the Philippines for single-nucleotide polymorphism on the sequences of Internal Transcribed Spacer (ITS) of rDNA genes and mtDNA indicated only few points of heteroplasmy. Nematode reproduction and disease induction of the five M. graminicola populations in the Philippines exerted the same level of aggressiveness and virulence. The absence of resistance-breaking populations of M. graminicola is important for the maintenance of durability of resistance to this important rice pathogen.