The root-lesion nematode, Pratylenchus penetrans, causes growth reduction in glasshouse-grown lettuce and is mainly controlled by chemical soil disinfestation. Integrated management strategies require more knowledge about the population dynamics and damage threshold densities. We monitored the population during 2.5 years in a commercial glasshouse by sampling soil in the same four 1 m2 spots at 0-30 cm and 30-60 cm depth. The grower grew lettuce in rotation with leek, applied 1,3-dichloropropene in summer and left the field fallow during winter. Growing leek reduced the nematode population slightly but chemical soil disinfestation lowered the numbers drastically, although 41% of the nematodes in the deeper layer survived. Black fallow resulted in a slight increase of the population, probably due to hatching. Two pot experiments with ten densities of P. penetrans were conducted to estimate the damage threshold for a summer and autumn cultivar (‘Cosmopolia’ and ‘Brighton’, respectively). The thresholds for lettuce weight were 669 and 3834 P. penetrans (100 ml soil)−1 in summer and autumn, respectively, but with considerable variability in estimated parameters. The thresholds for root damage were much lower: 204 and 48 P. penetrans (100 ml soil)−1. Nematode numbers did not increase on lettuce in the pot tests (maximum multiplication rate was 0.40) but increased slightly in the commercial setting. These results show that populations of P. penetrans build up slowly when butterhead lettuce is rotated with leek and fallow, but chemical soil disinfestation is required to avoid numbers resulting in root damage.
Paracrobeles psammophilus from the type locality is redescribed based on SEM studies. In addition, material of P. psammophilus previously described from Sicily (Italy) is revised. Species of Paracrobeles are analysed and form two morphological groups: the laterellus-group with three species (P. kelsodunensis, P. laterellus and P. mojavicus) having a lip region with two guard processes at both primary and secondary axils and shorter and more robust spicules, and the psammophilus-group with two species (P. deserticola and P. psammophilus) having primary axils bearing two guard processes and secondary axils with only one guard process and longer and slender spicules. Another four species (Acrobelinema cornis, Cervidellus cancellatus, C. rarus and C. sonorensis), having an intermediate morphology between Paracrobeles and Nothacrobeles, are transferred to Nothacrobeles (= Acrobelinema n. syn.).
Management of plant-parasitic nematodes in no-tillage systems relies on knowledge of the species, their abundance and their host range in a certain cropping area. Crop rotation is one of the most efficient techniques in the control of plant-parasitic nematodes; thus, the identification of non-host plant species is essential. Therefore, the aim of this study was to evaluate the host suitability of different cover crops used in crop rotations to control two of the most devastating plant-parasitic nematodes in the Brazilian central region, Meloidogyne javanica and M. incognita. Two experiments were conducted in a completely randomised design under glasshouse conditions. In the M. incognita experiment, seven treatments (cover crops) were evaluated: Crotalaria juncea (sunn hemp; CJ), Stylosanthes humilis (Townsville stylo; TS), Pennisetum glaucum (millet; M), Triticum aestivum (wheat; W), Mucuna aterrima (black mucuna, BM), Glycine max (soybean treated with nematicide (fluensulfona) (SN) and soybean without nematicide (SwN)). In the M. javanica experiment, nine treatments were evaluated: Cajanus cajan (pigeon pea), Brassica napus (canola), B. nigra (mustard), CJ, M, W, BM, SN and SwN. The evaluations were performed 60 days after inoculation, when eggs and juveniles were present in the plant roots and soil, and the nematode reproduction factors (RF) were determined. The results indicated that CJ, M and BM were effective in controlling M. javanica and M. incognita. The SwN and even SN resulted in high RF and were not effective in the control of M. javanica and M. incognita.
Helicotylenchus ciceri n. sp. and H. scoticus are described and illustrated based on morphological, morphometric and molecular characters. The new species is characterised by a conical and truncated lip region with five or six distinct annuli, stylet 32-37 μm long with anteriorly concave knobs, secretory-excretory pore posterior to the pharyngo-intestinal valve, dorsally convex-conoid tail with a terminal projection, phasmids 14 (7-20) annuli anterior to the level of anus, empty spermatheca and absence of males. Intraspecific variation of 16 populations of H. scoticus, collected from chickpea and lentil fields in Kermanshah province, western Iran, is discussed. The results of the phylogenetic analyses based on the sequences of the partial 18S rRNA, D2-D3 expansion segments of 28S rRNA and ITS rRNA genes are provided for the studied species, confirming their differences from each other and determining the position of them and their relationships with closely related species.
There is no single feature to distinguish free-living soil nematodes from freshwater nematodes, also because all free-living nematodes are essentially aquatic. This notwithstanding, by examining the frequencies of some characters of 1141 European species, differences of qualitative/quantitative characters between soil and freshwater nematodes were found. In particular, aquatic and semi-aquatic species are, on average, longer and slimmer than soil species, have a longer tail, greater body weight, smooth cuticle and larger amphids. A new body parameter, length of the pharynx in relation to the length of the whole digestive tract (e), was also taken into consideration.
The aim of this study was to examine the impact of water extracts of Narcissus tazetta bulb on hatching, behaviour and mortality of second-stage juveniles (J2) and reproduction of the soybean cyst nematode (SCN; Heterodera glycines) in laboratory and glasshouse assays. Results demonstrated that N. tazetta bulb extracts did not affect hatching but significantly reduced J2 motility and nematode attraction to the soybean root tip, and resulted in considerable nematode mortality relative to the control. J2 exposure to different concentrations of bulb extracts caused 59-93% reduction in nematode reproduction on soybean roots. Compared with the monoculture control, soybean-N. tazetta intercropping in a pot trial reduced SCN reproduction by 37%. In addition, N. tazetta bulb powder as a soil amendment is effective in controlling SCN reproduction. Thus, the results suggest that N. tazetta bulb extract or derived active compounds may be considered as potential natural nematicides against SCN.
Morphological observations were made on paratypes and populations of 11 species of Amplimerlinius, including A. amplus, A. clavicaudatus, A. globigerus, A. icarus, A. intermedius, A. macrurus, A. magnistylus, A. nectolineatus, A. paraglobigerus, A. siddiqii, and A. uramanatiensis, deposited in various international nematode collections. Results showed that A. clavicaudatus differs from other Amplimerlinius species by having four lateral incisures at the deirid level, the tail terminus has a refractive inner cuticle layer, and there is a less thickened hyaline region at the tail terminus. As the latter species shares its main morphological characteristics with Paramerlinius, it is proposed herein to transfer this species to Paramerlinius as P. clavicaudatus n. comb. (= A. clavicaudatus).
The study of soil nematode communities is a powerful tool that has been widely used as an indicator of soil health. This study explored whether soil nematode composition of different land use types could be used as a baseline to indicate the soil health of both natural and anthropogenic ecosystems. The soil nematode community compositions were documented for five land use types in tropical China: bare land, secondary forest, old forest, eucalyptus plantation and litchi orchards. The first three land use types are natural ecosystems and considered as a vegetation succession, whereas the other two are anthropogenically managed ecosystems. The vegetation succession from bare land to secondary and old forests increased soil nematode abundance, diversity, diversity-weighted abundance and complexity of community structure. During the wet season, the abundances of the total nematodes, bacterivores, fungivores and herbivores were significantly lower in eucalyptus plantation and litchi orchards than in secondary and old forests, but higher than in bare land. During the dry season, the abundances of the total nematodes and each trophic group were greatest in orchards. The pattern of the diversity-weighted abundance of each nematode trophic group was similar to that of nematode trophic group abundance. The results indicate that soil nematode communities of different land use types could be used for comparison of soil health conditions in natural and managed ecosystems. Particularly, the soil health conditions as indicated through nematode communities of the two managed ecosystems were not as good as those of secondary and old forests, whereas litchi orchards might have better soil health conditions than eucalyptus plantations in tropical China.
Within sub-Saharan Africa (SSA), although nematodes are viewed among the most important threats to crop production and food security, the presence of trained nematologists working within this discipline has traditionally been viewed as scarce. The few research studies concerning this subject address this topic from a country or sub-regional perspective and generally portray nematology as ‘insufficient’. Over the past two decades, a few initiatives have been instrumental in building greater nematology expertise. For the first time a structured survey was undertaken, involving interviews with individuals from SSA that were (or currently are) involved in nematology training programmes, research, national extension services or in African universities. This paper provides evidence of the positive impact of various initiatives and shows an increase in the number of available nematology positions, together with high rates of graduates that return home to occupy qualified positions. Our findings will help researchers, policy makers and donors to identify areas requiring support to increase the promotion of nematology in SSA and to make an impact for end-users.