Journal of nematology最新文献

This experiment investigates five small grain winter cover crops including multiple genotypes of barley (Hordeum vulgare L), oats (Avena sativa L.), rye (Secale cereale L.), triticale (x Triticosecale Wittmack), and wheat (Triticum aestivum L.) as a sustainable nematode management strategy for Meloidogyne incognita (root-knot nematode) and Rotylenchulus reniformis (reniform nematode) in cotton production in a Southeastern U.S. Greenhouse (2019), and field experiments (2019-2021) evaluated these crops for nematode host status, forage quality, and grain yield. Greenhouse experiments showed that all small grains had higher average M. incognita egg counts than a standard corn (Zea mays L.) variety. Overall, barley and wheat were suitable hosts (Rf>2), triticale and oat were moderate hosts (Rf=1-2), while three cultivars (Forerunner' and 'OG170039' triticale, "ORO 4372' oat) were poor hosts (Rf<1). In field trials, oat had the highest biomass and grain yield, followed by triticale, barley, rye, and wheat. Barley supported the highest population density of M. incognita. Oat, barley, and rye displayed similar population density of R. reniformis and were greater than triticale and wheat. Forage quality experiments showed oat with the highest biomass, wheat with the highest crude protein, and rye and triticale leading in fiber content. Oats had the greatest total digestible nutrients (TDN) and relative feed value (RFV), indicating superior digestibility. All small grains demonstrated high forage quality (RFV>100). Cover crop selection should be based on specific management and agronomic goals as nematode populations varied by cover crop but were low in all field trials. Further research on crop-specific responses and long-term effects on nematode populations and soil health is needed to optimize small grain winter cover crops in integrated pest management programs.

Entomopathogenic nematodes (EPNs) used as biocontrol agents are sensitive to ultraviolet (UV) light, high temperature, and desiccation. Thus, formulations have been developed to protect EPNs during application. However, the ability of these formulations to enhance storage capacity has not been investigated. This study analyzed storage capacity (survival and efficacy) of EPN species, Heterorhabditis bacteriophora (SGI 245), Steinernema tophus (ROOI 352) and Steinernema innovationi (SG I35) produced either in vivo or in vitro and formulated in 2% gel of either Barricade^® or potassium polyacrylate hydrogel (PPH). The formulations were stored at 10°C and survival of the infective juvenile nematodes (IJs) was evaluated at two-weeks intervals for eight weeks. The efficacy of formulated nematodes was evaluated using Tenebrio molitor. After two weeks, all control treatments had 0% IJ survival for all the three isolates, whereas the gel formulations exhibited 58-76% survival. The three isolates in both the Barricade^® gel and PPH formulations exhibited 37-69% IJ survival at six weeks, which declined to 0-13% after eight weeks. Both formulations of the three isolates were 60-90% effective at six weeks. The in vitro-produced IJs had a higher survival than the in vivo-produced IJs for S. innovationi and H. bacteriophora. However, the in vivo-produced IJs were more effective at killing T. molitor than the in vitro-produced EPNs for H. bacteriophora but not the Steinernema spp. In conclusion, Barricade^® and PPH gel formulations substantially increased survival of the three EPN species during storage.

A new species of the genus Geraldius isolated from the wood of a dead black pine tree is characterized using morphological data and molecular DNA barcodes. Geraldius jejuensis n. sp. is characterized by its lateral fields with two incisures; lip region conoid to rounded and continuous with body; hemizonid and excretory pore located posterior to nerve ring; excretory pore opening just at the beginning of hemizonid or within the contour of hemizonid; vulva a transverse slit in ventral view; opening in a depression, creating a circular profile in lateral view; rectum 1.4 to 1.7 times longer than anal body diameter; phasmids located 55.0 to 78.5 μm from anal opening; tail elongated, 146.0 to 177.0 μm long; gubernaculum 27.0 to 33.5 μm long, caudal papillae arrangement of seven pairs pre-cloacal, two adcloacal, and six post-cloacal; and three additional midventral papillae on anterior cloacal lip. The new species was compared with the three known species of the genus, including G. bakeri, G. galapagoensis and G. inserrai. The phylogenetic relationships among species were reconstructed using 18S-rRNA and 28S-rRNA gene sequences. Inferences from both genes corroborate the close morphological relationships between Geraldius and Diastolaimus.

Nematodes such as Caenorhabditis elegans and Pristionchus pacificus are powerful models for associating phenotypes to genotypes. However, exploring the evolution of identified genetic loci requires a robust phylogenomic framework. Here, we present an updated genome of the nematode Parapristionchus giblindavisi which is the only known member of the sister group of Pristionchus. Reassembly of previously generated long read sequencing data combined with new Hi-C data resulted in a near chromosome-scale genome assembly spanning 302.5Mb. The Hi-C contact map, karyotyping data and comparative genomic analysis support an organization of the P. giblindavisi genome into six chromosomes, whereby all autosomes correspond to individual Nigon elements and the sex chromosome represents a fusion of Nigon elements D and X. The further improved P. giblindavisi genome will be useful as an outgroup for dating and polarizing lineage-specific genomic signatures.

[This corrects the article DOI: 10.2478/jofnem-2023-0033.].

Research efforts are needed to develop new biocontrol strategies against plant-parasitic nematodes (PPNs) to replace chemicals and maintain sustainable crop production. In this study, filtrates obtained from fungi isolated from cyst nematodes (Heteroderidae) were evaluated for activity against eggs and second-stage juveniles (J2) of five PPNs: Globdera ellingtonae, Heterodera glycines, Meloidogyne incognita, M. hapla, and M. chitwoodi. Initially, filtrates of 42 fungal isolates were evaluated for effects on G. ellingtonae and H. glycines egg viability. After the initial screening, six of the fungal isolates were selected for further evaluation against additional PPN eggs and J2 based upon evidence of usage in other studies, fast growth, and frequency of isolation. Filtrates from Alternaria tenuissima JB217, Fusarium acaciae-mearnsii JB201, Purpureocillium lilacinum JB209, and Trichoderma virens JB98 reduced H. glycines egg viability by >80%. Aureobasium sp. JB70, F. proliferatum JB173, and P. lilacinum JB209 reduced G. ellingtonae egg viability by >50% but had negligible effect on the J2 stage of this nematode. Filtrate from F. acaciae-mearnsii JB201was the most lethal against PPNs, immobilizing ~100% of J2 of all nematode species while filtrate from A. tenuissima JB217 only immobilized J2 of G. ellingtonae, M. chitwoodi, and M. hapla. These fungal filtrates are therefore promising alternative sources of natural bioactive substances for the potential management of PPNs.

Philaenus spumarius specimens were found naturally parasitized by Mermithidae nematodes in Central Italy. Nematodes infected all spittlebug instars, showing a highly variable parasitization rate according to sampling locations. Molecular analysis highlighted the presence of two distinct species that are apparently not cohabitant in the same site. However, complete taxonomic identification will occur when adult nematodes are obtained. Further research is needed to identify these two putative nematode species and to understand their ecological requirements. Furthermore, new studies aimed to elucidate the relationship between P. spumarius and Mermithidae nematodes, as well as the role of these parasites in regulating spittlebug populations, can be useful in identifying potential natural enemies for pest control. To our knowledge, this is the first report of Mermithidae infecting P. spumarius in Europe.

Calcium alginate beads are one of the substrates used to formulate and store the infective juveniles (IJs) of entomopathogenic nematodes (EPNs). Due to the sensitivity of EPNs to heat, cooling devices are needed to transfer them from the production site to the field or greenhouse. Therefore, it is important to develop a formulation that can be stored at room temperature. The hypothesis of this study was that nematodes formulated in alginate beads would be more stable at room temperature than in sterile water. To compare and select the optimal conditions, formulations were tested at two temperatures: 25 and 8 Celsius (ºC). The formulation included sodium alginate (1.5-1.75%), glycerin, nematode suspension in distilled water (~15,000 IJs), food coloring, and two proprietary water-absorbent compounds. The suspension was added to CaCl₂ (8:2 CaCl₂: glycerin) to create calcium alginate beads. The beads were stored at 8 ºC and 25ºC with a control treatment consisted of sterile water. The study measured survival, reproduction rate, and infectivity of Heterorhabditis bacteriophora, Steinernema carpocapsae, and S. feltiae IJs in calcium alginate beads over time (1-180 days post-formulation). The survival rate of IJs in bead formulations was significantly higher than in the water control treatment. H. bacteriophora experienced higher survival at 25ºC, while S. carpocapsae experienced higher survival at 8ºC. S. feltiae's survival was not affected by temperature. The pathogenicity of EPNs did not decrease over time. Calcium alginate effectively encapsulated living IJs of various EPN species, keeping them alive for up to three months at room temperature. These results suggest that alginate beads are a suitable material for EPNs formulation. Further research is needed to enhance the efficacy and economic viability of these formulations.

Helicoverpa zea is a major agricultural pest, particularly in cotton, and poses significant challenges due to its ability to develop resistance to chemical insecticides. This study evaluates the efficacy of the entomopathogenic nematode (Steinernema adamsi) and its mutualistic bacteria (Xenorhabdus) as biological control agents against H. zea larvae in both laboratory and field settings. In laboratory assays, mortality rates for 1^st to 4^th instars were high, ranging from 74.2% to 100%, while 5^th instars exhibited significantly lower susceptibility (<37% mortality). Pupae were completely resistant to nematode infection. The impact of UV radiation on nematode efficacy was assessed, with mortality decreasing from 100% in control conditions (0 hours of UV exposure) to 71.8% after 5 hours of UV exposure, highlighting the vulnerability of S. adamsi to UV degradation. In addition, Xenorhabdus caused 100% mortality in H. zea larvae when injected directly into the hemocoel, but oral toxicity was significantly lower, with 36% mortality in 7 days post-exposure. Field experiments demonstrated that the combination of S. adamsi with 0.05% sodium alginate (hygroscopic agent) and 0.02% Congo red (UV protectant) resulted in a significant increase in larval mortality. In field test A, where S. adamsi was applied in water, mortality averaged 56% with 82% EPN infection. In field test B, the combined treatment of sodium alginate and Congo red led to 98% larval mortality, although infection rates were lower and statistically non-significant. The addition of these protective agents likely enhanced the environmental stability and efficacy of the nematodes under field conditions. These findings suggest that S. adamsi can be an effective biological control agent for H. zea, particularly when combined with formulations that protect against UV radiation and desiccation. Future research should focus on optimizing nematode delivery systems to improve field efficacy under diverse environmental conditions.

Meloidogyne enterolobii, is an emerging root-knot nematode species in the southern United States. To date, no studies have evaluated the host status of onions to M. enterolobii. This study aimed to assess the reproduction and pathogenicity of M. enterolobii on onion cultivars commonly grown in Georgia. Six Vidalia onion cultivars ('Rio del Sol', 'Sapelo', 'Sweet Magnolia,' 'Tania,' 'Vidora,' and 'NUN 1011'), three red onion cultivars ('Red Duke,' 'Red Halen,' and 'Red Maiden'), and a white onion cultivar ('Monjablanca') were evaluated. Each cultivar was inoculated with 8,000 eggs of M. enterolobii in a repeated greenhouse trial with six replications each. Twelve weeks post-inoculation, plants were harvested to determine reproduction and pathogenicity based on the reproduction factor (Rf = final nematode population/initial nematode inoculum) and reductions in bulb and shoot weights, respectively. All tested cultivars were susceptible to M. enterolobii, with Rf values greater than 1, though significant differences were observed. 'Vidora' and 'Tania' exhibited the highest galling index and Rf values, while 'Sweet Magnolia' and 'Sapelo' had the lowest. All red onion cultivars showed significant reductions in weight for both bulbs and shoots, whereas among the Vidalia cultivars, only 'NUN 1011' exhibited notable reductions in bulb and shoot weights. These findings suggest that onions are suitable hosts for M. enterolobii, and that the nematode's reproduction and pathogenicity vary with onion type and cultivar.