Journal of nematology最新文献

Nematodes play a vital ecological role in soil and marine ecosystems, but there is limited information about their dietary diversity and feeding habits. Due to methodological challenges, the available information is based on inference rather than confirmed observations. The lack of correct dietary requirements also hampers rearing experiments. To achieve insight into the prey of mononchid nematodes, this study employed high-throughput Illumina paired-end sequencing using universal eukaryotic species 18S primers on 10 pooled mononchid nematode species, namely Mylonchulus brachyuris, M. brevicaudatus, Mylonchulus sp., Clarkus parvus, Prionchulus sp. M. hawaiiensis, M. sigmaturellus, M. vulvapapillatus, Anatonchus sp. and Miconchus sp. The results indicate that mononchids are associated with a remarkable diversity of eukaryotes, including fungi, algae, and protists. While the metabarcoding approach, first introduced here for mononchids, proved to be a simple and rapid method, it has several limitations and crucial methodological challenges that should be addressed in future studies. Ultimately, such methods should be able to evaluate the dietary complexity of nematodes and provide a valuable avenue for unraveling the dietary requirements of previously unculturable nematodes. This can contribute to the methodology of understanding their feeding habits and contributions to ecosystem dynamics.

Plant-parasitic nematodes (PPN) are an understudied pathogen group in the Oregon cool-season grass seed cropping system. In this survey, the PPN associated with annual ryegrass, bentgrass, fine fescue, orchardgrass, perennial ryegrass, and tall fescue were determined. Thirty-seven fields were sampled in the 2022 or 2023 growing season by collecting 10 soil cores in each of six 100-m transects for nematode extraction and visual identification. PerMANOVA testing indicated significant differences in PPN community composition across grass host and sampling time. Pratylenchus and Meloidogyne were the most commonly encountered nematodes, with maximum population densities of 1,984 and 2,496 nematodes/100 g soil, respectively. Sequencing of the COX1 gene region indicated the presence of P. crenatus, P. fallax, P. neglectus, P. penetrans, and P. thornei, with some of these species being detected for the first time on these grass hosts. The only Meloidogyne sp. found in these grasses was M. nassi, based upon sequencing of the ITS gene region. This first-of-its-kind survey indicates the need for further assessment of the impact of these PPNs on yield and stand longevity in cool-season grass seed fields in Oregon.

In the southern United States, corn earworm, Helicoverpa zea (Boddie), and soybean looper, Chrysodeixis includens (Walker) are economically important crop pests. Although Bt crops initially provided effective control of target pests such as H. zea, many insect pests have developed resistance to these Bt crops. Alternative approaches are needed, including biological control agents such as entomopathogenic nematodes (EPNs). However, the effectiveness of EPNs for aboveground applications can be limited due to issues such as desiccation and ultraviolet radiation. Effective adjuvants are needed to overcome these problems. Ten strains of EPNs were tested for virulence against eggs, first to fourth instars, fifth instars, and pupae of H. zea and C. includens in the laboratory. These 10 EPN strains were Heterorhabditis bacteriophora (HP88 and VS strains), H. floridensis (K22 strain), Hgkesha (Kesha strain), Steinernema carpocapsae (All and Cxrd strains), S. feltiae (SN strain), S. rarum (17c+e strain), and S. riobrave (355 and 7-12 strains). EPNs could infect eggs of H. zea or C. includens in the laboratory, but the infection was low. The mortality caused by 10 EPN strains in seven days was significantly higher for the first to fourth instars of H. zea compared to the control, as was the fifth instars of H. zea. Similarly, for the first to fourth and fifth instars of C. includens, the mortality was significantly higher compared to the controls, respectively. However, only S. riobrave (355) had significantly higher mortality than the control for the pupae of H. zea. For the pupae of C. includens, except for H. bacteriophora (HP88), S. rarum (17c+e), and H. floridensis (K22), the mortality of the other seven strains was significantly higher than the control. Subsequently, S. carpocapsae (All) and S. riobrave (7-12) were chosen for efficacy testing in the field with an adjuvant 0.066% Southern Ag Surfactant (SAg Surfactant). In field experiments, the SAg Surfactant treatment significantly increased the mortality and EPN infection for S. carpocapsae (All) on first instars of H. zea in corn plant whorls. On soybean plants, with the SAg Surfactant, S. carpocapsae (All) was more effective than S. riobrave (7-12) on fifth instars of C. includens. This study indicates that EPNs can control H. zea and C. includens, and SAg Surfactant can enhance EPN efficacy.

Viviparity is generally considered to be rare in animals. In nematodes, only six species of Rhabditida are viviparous. Five of these species have been identified in association with Onthophagus dung beetles, with Tokorhabditis atripennis being repeatedly isolated from the dung beetle Onthophagus atripennis in Japan. T. atripennis is easy to culture in a laboratory setting, and its host, O. atripennis, is distributed all over Japan. Therefore, T. atripennis is an ideal candidate for ecological and evolutionary studies on viviparity. However, the extent of their distribution and relationship with dung beetles, as well as habitats, remain unclear. In the present study, we conducted field surveys and successfully isolated 27 strains of viviparous nematodes associated with tunneler dung beetles from various regions of Japan, all of which were identified as T. atripennis. T. atripennis exhibited a strong association with Onthophagus dung beetles, especially O. apicetinctus and O. atripennis. And it was predominantly found in specific anatomical locations on the beetle bodies, such as the 'groove between pronotum and elytron' and the 'back of the wings'. Our findings suggest that Onthophagus species are the primary hosts for T. atripennis, and T. atripennis exhibits a close relationship with the living environments of tunneler beetles. This association may play a significant role in the evolution of viviparity in nematodes.

Infective second-stage juveniles (J2) of Meloidogyne spp. migrate towards host roots, which depends on several factors, including root exudates and soil temperature. Although Meloidogyne enterolobii is a highly virulent nematode that affects major agricultural crops worldwide, there is limited ecological data about it. The objective of this study was to determine the J2 migration pattern vertically in 14-cm long segmented soil columns towards tomato (Solanum lycopersicum) and marigold (Tagetes patula) roots, each grown at two soil temperatures (20 or 26ºC). Bottomless cups with tomatoes or marigolds were attached to the top of each column; cups with no plants were used as untreated controls. Juveniles (1,000/column) were injected into a hole located 1 cm from the bottom of each column. The apparatuses were placed in growth chambers at 20 or 26ºC, and J2 were allowed to migrate for 3, 6, 9, or 12 days after injection (DAI). At each harvest, J2 were extracted from each ring of the columns and counted to compare their distribution, and root systems were stained to observe root penetration. M. enterolobii migrated over 13 cm vertically 3 DAI regardless of temperature, even without plant stimuli. The vertical migration was greater at 26ºC, where 60% of active J2 were found at distances >13 cm at 12 DAI. Temperature did not affect root penetration. Overall, a greater number of J2 was observed in tomato roots, and root penetration increased over time.

The reniform nematode, Rotylenchulus reniformis, is a major yield-limiting pest of upland cotton (Gossypium hirsutum) in the United States that has been steadily increasing in incidence in many states. Reniform nematode-resistant cotton cultivars have recently become commercially available for cotton producers; however, few field trials have evaluated their efficacy as a nematode management tool. The aim of this study was to evaluate reniform nematode population development, plant growth, and seed cotton yield of reniform nematode-resistant cotton cultivars in two nematode-infested fields in Louisiana. Replicated small-plot field trials were conducted in St. Joseph, LA (NERS field) and Winnsboro, LA (MRRS field) during the 2022 and 2023 growing seasons. In 2022, cultivars evaluated included: (1) DP 1646 B2XF (susceptible/tolerant), (2) DP 2141NR B3XF (resistant), (3) PHY 332 W3FE (resistant), (4) PHY 411 W3FE (resistant), and (5) PHY 443 W3FE (resistant). In 2023, an additional susceptible cotton cultivar, PHY 340 W3FE, was also included. All nematode-resistant cotton cultivars evaluated provided suppression of reniform nematode population development relative to that of the susceptible cotton cultivars, with suppression of nematode soil population densities at harvest ranging from 49 - 81% relative to DP 1646 B2XF. The resistant cultivar PHY 411 W3FE provided the most consistent suppression of reniform nematode population development, reducing reniform nematode soil population densities at harvest in both field locations and both trial years. In contrast, DP 2141NR B3XF only reduced soil population densities at harvest in the NERS field in 2023. Despite relatively consistent nematode suppression and improvements in plant vigor ratings and canopy coverage associated with the resistant cotton cultivars, a yield increase was only observed with PHY 332 W3FE and PHY 411 W3FE planted at the NERS field in 2023. Despite strong resistance to reniform nematode in the evaluated cotton cultivars, nematode soil population densities still increased during the growing season in plots planted with resistant cotton cultivars, emphasizing the need for additional management tactics to use alongside host resistance. This study indicates that new reniform nematode-resistant cotton cultivars show promising potential to reduce nematode population development during the growing season in Louisiana.

Weeds that compete with valuable crops can also host plant-parasitic nematodes, acting as a source of nematode inoculum in a field and further damaging crops. The host status of 10 weed species commonly found in North Carolina, USA, was determined for the root-knot nematodes Meloidogyne enterolobii and M. incognita race 4 in the greenhouse. Each weed species was challenged with 5,000 eggs/plant of either M. enterolobii or M. incognita race 4, with five replicate plants per treatment in two separate greenhouse trials. Root galling severity and total number of nematode eggs per root system were recorded 60 days after inoculation. Reproduction factor (Rf = final nematode population/initial nematode population) was calculated to determine the host status of each weed species to M. enterolobii and M. incognita race 4. Four weed species (Datura stramonium, Digitaria sanguinalis, Senna obtusifolia, and Cyperus esculentus) were poor hosts (Rf < 1) to both nematode species, and roots of these weed plants did not display galling. Four weed species (Ipomoea hederacea, Amaranthus palmeri, Portulaca pilosa, and Ipomoea lacunosa) were hosts (Rf > 1) to both nematode species, and all had observable root gall formation. Sida rhombifolia and Cyperus rotundus were poor hosts to M. enterolobii but susceptible hosts to M. incognita. This study documents a differential host status of some common weeds to M. enterolobii and M. incognita race 4, and these results highlight the necessity of managing root-knot nematodes through controlling weeds in order to protect valuable crops.

Nothotylenchus savadkoohensis n. sp. was recovered from rotten wood samples of an unidentified forest tree in the Mazandaran province and described herein. It is mainly characterized by an elongated conoid tail ending in a sharply pointed tip and four lines in the lateral field. Females of the new species have 379-662 μm long bodies with 5.8-6.9 μm long stylets ending in fine posteriorly sloping knobs, the metacorpus not valvate, the pharyngeal bulb slightly overlapping the intestine, and the vulva at 76.5-84.0% of body length. Males are also common and have 13.0-14.5 μm long spicules and bursa cloacal. By having an elongated conoid tail and four lines in the lateral field, the new species comes close to four known species, namely N. acris, N. acutus, N. antricolus, and N. truncatus. The morphological differences between the new species and the abovementioned species are discussed. The new species was sequenced for its D2-D3 segment of LSU and ITS rDNA regions. In the LSU phylogenetic tree, the currently available LSU sequences of the genus Nothotylenchus occupied distant placements from each other and the LSU sequence of the new species formed clade with a sequence assigned to Neotylenchus sp. In ITS phylogeny, the newly generated sequence of the new species formed a clade with a clade that includes sequences of Ditylenchus sp. and Neomisticius platypi and N. variabilis.

Metaparasitylenchus hypothenemi is a nematode that naturally parasitizes Hypothenemus hampei in a coffee-producing region in Chiapas, Mexico. This study investigated changes in the attraction of parasitized borers to light. We compared the attraction of adult H. hampei females (parasitized and uninfected) to 14 different light wavelengths (350-670 nm) with a control (570 nm, yellow) under laboratory conditions. The response ranges of non-parasitized and parasitized borers were 370-650 nm and 340-650 nm, respectively. The attraction curve showed a similar shape in both borer groups (parasitized and non-parasitized), but a wide wavelength range (380-590 nm) attracted more parasitized than non-parasitized borers. The maximum response of the uninfected borers occurred at 520 nm (green), while parasitized borers exhibited three response peaks (380 nm, violet; 460 nm, blue; 520 nm, green). Parasitized borers were significantly more attracted to green light (520 nm) than to the control. The altered attraction to light in borers parasitized by M. hypothenemi is discussed from the perspective of possible host manipulation and the natural prevalence of this parasite.

The prevalence of Heterodera glycines and other cyst and vermiform genera was determined from 8,009 soil samples over two decades. Prevalence of cyst nematodes for farms increased from 16% in 1998 to 1999, reaching a peak of 40%, with marked differences among Wisconsin's nine agricultural districts in how much the odds of a positive test increased. Estimates at the sample scale also increased over time but peaked at 29%. Assay of all nematodes beginning in 2012 showed Pratylenchus, Helicotylenchus, and Xiphinema to be more prevalent in Wisconsin soybean fields than cyst nematodes. Prevalence estimates for Pratylenchus and Helicotylenchus for soybean and rotation crops ranged from 76 to 89% and 58 to 83%, respectively. Species identification of Pratylenchus from a subset of the samples revealed six species. The majority of cyst-positive samples were infested with Pratylenchus, and count data showed that the number of cyst eggs and juveniles per 100 cm³ soil was 60% lower in samples positive for Pratylenchus. The influence was reciprocal, as Pratylenchus population densities were 41% lower in samples positive for cyst nematodes, suggesting a competitive interaction. The Wisconsin soybean nematode testing program provides a useful model for estimating nematode prevalence using citizen-based surveys.