Journal of nematology最新文献

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.

Meloidogyne arenaria (peanut root-knot nematode, PRKN) is an important pest in peanut (Arachis hypogea) production in the United States, including specialty Virginia-type peanuts. Cultivars resistant to PRKN and nematicide application are two available methods for managing PRKN. The objectives of this study were to determine the impacts of resistant Virginia-type peanut cultivars (Georgia-19HP and TifJumbo) on (1) management of PRKN abundances and damage and (2) total free-living nematode soil abundances. A common susceptible cultivar (Bailey II) with or without in-furrow fluopyram nematicide was compared to the resistant cultivars without nematicide in field trials in Florida (2022 and 2023). Resistant cultivars reduced midseason PRKN abundances from roots by 92-98% and final PRKN soil abundances by 81-93% relative to the untreated susceptible cultivar. Fluopyram reduced midseason PRKN root abundances by 65-74% and final PRKN soil abundances by 42-51% relative to untreated susceptible. Although PRKN reproduced on peanuts, no damage symptoms were observed, yield did not vary by treatment in 2022, and yield was significantly greater for fluopyram than either resistant cultivar in 2023. Impacts on total free-living nematode soil abundances were inconsistent. In summary, either fluopyram or resistant cultivars are effective tools for managing PRKN abundances in Virginia-type peanuts.

Meloidosgyne fallax (false Columbia root knot nematode) is an invasive crop pest recorded across Europe, Africa, North America, and Oceania. Here we present the draft genome assembly of M. fallax which was de novo assembled and scaffolded using M. chitwoodi (Columbia root knot nematode), a close relative of M. fallax.

Interest in organic production is growing, highlighting the need for effective organic integrated management practices for sweetpotatoes. This study aimed to evaluate biopesticides and cover crops for managing Meloidogyne incognita in greenhouse and microplot settings. In the greenhouse, M. incognita reproduction factors were highest following field pea at 15.3 and crimson clover at 5.0, while daikon radish, elbon rye, and cover crop mixes had the lowest factors near 1.0. Summer cover crops sunn hemp, velvetbean, and 'Piper' sudangrass did not support M. incognita populations, with reproduction factors below 1. Greenhouse tests revealed similar M. incognita egg numbers/gram of root across all biopesticides, with MeloCon maintaining the lowest numbers. Microplot testing of the biopesticides on sweetpotatoes found M. incognita populations were similar to MeloCon, BotaniGard 22 WP plus Triple Threat Entomopathogenic Nematodes, Chitocide, Seduce, Promax, and Minuet. The highest marketable yield of 0.56 kg/plant was recorded in microplots treated twice with Chitocide, followed by BotaniGard 22 WP plus Triple Threat Entomopathogenic Nematodes, AzaGuard, and Majestene, all of which were comparable to synthetic nematicide, Velum applied at planting. In two field microplot trials, winter cover crops, black oat, daikon radish, and cover crop mixes of all cover crops tested produced the highest sweetpotato yield. Daikon radish, elbon rye, crimson clover, cover crop mix, black oats, and yellow mustard supported lower nematode populations compared to field peas. Overall, all cover crops tested, except field peas and crimson clover, reduced the M. incognita populations during the cover cropping season. Biopesticide MeloCon was most effective in reducing M. incognita populations post sweetpotato planting.

Root-knot nematodes (RKN; Meloidogyne spp.) are among the most damaging plant-parasitic nematodes. They parasitize almost every species of higher plant and induce the formation of galls along the plant roots, which are detrimental to plant growth. North Carolina's leading field crops are sweetpotato (Ipomoea batatas (L.) Lam.), soybean (Glycine max L. Merr), cotton (Gossypium hirsutum L.), and tobacco (Nicotiana tabacum L.), which are all hosts to several root-knot nematode species. This pathogen represents a major threat to farmers, obligating them to seek alternative crops that are non-host to root-knot nematodes that will help decrease soil populations and provide economic revenue. We tested seven sesame cultivars for their host status and potential resistance to four Meloidogyne species (M. arenaria, M. incognita, M. enterolobii, and M. hapla). We inoculated sesame seedlings with 1,000 nematode eggs of each species. Sixty days after inoculation, we harvested the plants to evaluate a visual gall severity rating, measure final egg counts, and calculate the reproductive factor (RF). All sesame cultivars had a significantly lower RF than the tomato (Solanum lycopersicum L.) cv. Rutgers control for all species of RKN except M. arenaria. The RF values for sesame cultivars inoculated with M. incognita and M. hapla were not significantly different from one another; however, there were significant differences in RF among sesame cultivars inoculated with M. enterolobii, suggesting that genetic variability of the host may play an important role in host status and conferring resistance.

A new species of the genus Deladenus isolated from a dead red pine tree was characterized using morphometric and molecular DNA data. Deladenus uljinensis n. sp. is characterized by its lateral fields with six to seven lines, pharyngeal corpus without a distinct median bulb and lacking a chamber, esophageal-intestinal junction located immediately behind the nerve ring, hemizonid located posterior to nerve ring, excretory pore opening within the contour of hemizonid or just at the base of hemizonid, vulva with no lateral vulval flaps, post-uterine sac rudimentary or absent, vulva-anus distance ca. equal to tail length, tail conoid, gradually tapering to a broadly rounded terminus, and slender spicules, 18.5-21.5 μm long. The new species was compared with morphologically close species including D. gilanica, D. brevis, D. pakistanensis, D. oryzae, D. uteropinusus, D. aridus, and D. durus. Additionally, D. posteroporus was also characterized and the population represents the first record of the species outside its type locality. The phylogenetic relationships among species were reconstructed using 18S-rRNA, 28S-rRNA and COI gene sequences. Inferences from the more informative 28S-rRNA gene suggest that D. uljinensis n. sp. is a sister species to the morphologically close D. gilanica.