Journal of nematology最新文献

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.

The small hive beetle (SHB), Aethina tumida Murray (Coleoptera: Nitidulidae), has become a ubiquitous, invasive, and highly destructive pest of western honeybee (Apis mellifera Linnaeus) hives worldwide. Beekeepers often attempt to control this beetle chemically. Still, ineffective registered control options and rampant off-label chemical use in the beekeeping industry have driven research toward alternative pest management strategies. Entomopathogenic nematodes (EPNs) of the families Heterorhabditidae and Steinernematidae have been established as potential biocontrol agents against soil-dwelling insect pests. However, studies are needed to determine the most appropriate EPN species to control SHB. In this study, an LD₅₀ of ~700 infective juveniles (IJs) of EPN per SHB larva was determined through dose-response experiments. This application rate was used to compare the virulence of the following seven species of EPNs against SHB larvae: Heterorhabditis bacteriophora (VS), H. floridensis (K22), H. georgiana (Kesha), H. indica (HOM1), Steinernema carpocapsae (All), S. rarum (17C+E), and S. riobrave (355). Steinernema carpocapsae (All) and H. floridensis (K22) were found to cause 100% larval mortality of SHB at 14 days post-inoculation. Assays for the persistence of virulence of H. floridensis (K22) and S. carpocapsae in the soil over several weeks from a single application found that both species maintained efficacy, causing 96% mortality of SHB larvae by week 6 post-inoculation. We recommend that S. carpocapsae (All) and H. floridensis (K22) due to their superior virulence for the control of small hive beetles.

Entomopathogenic nematodes (EPNs) have a specialized infective juvenile stage (IJ) that is mobile and has the capability to seek insect hosts to penetrate their haemocoel. EPNs are primarily applied to soil as biological control agents; thus, the IJs must move through the soil to find and infect a host. Soil characteristics are known to be an important factor that can affect the efficiency of EPN movement behavior. Previous research has shown that exposure to ascaroside pheromones can enhance EPN movement and infectivity in soil. The ability of pheromones to enhance EPN efficacy was recently demonstrated under field conditions in a pecan orchard. However, prior to our research, it was unknown whether different soils have differential effects on pheromone enhanced EPN efficacy. In different soils, we tested the biocontrol efficacy of Steinernema carpocapsae, Steinernema feltiae and Heterorhabditis bacteriophora in soil columns with and without pheromone exposure. All nematodes were evaluated in separate columns filled with oven dried commercial play sand and two different soils from pecan orchards (from Byron, GA and Tifton, GA). The soils differed substantially in several aspects such as field capacity, organic matter, nutrients, and nematode movement capacity. Efficacy was determined by baiting the bottom section of each column with larvae of the yellow mealworm (Tenebrio molitor L.). Results indicated that pheromones enhanced EPN efficacy for all EPN species and soils tested compared to treatments without pheromones. The magnitude/extent that pheromones boosted EPN movement in all EPNs regardless of soil type did not differ. Soil did not affect EPN efficacy for H. bacteriophora but did affect S. carpocapsae and S. feltiae. For both S. carpocapsae and S. feltiae efficacy was highest in the sandy field soil (Tifton soil) followed by that of the loamy sand (Byron soil) and pure sand (commercial play sand). When comparing the efficacy of EPN species to each other, we observed that H. bacteriophora killed more bait insects exposed to soil in the bottom of the soil column than other EPNs. Our findings suggest that pheromones can be used to enhance EPN efficacy in diverse soils. Future research may explore pheromone effects on EPNs in additional substrates.

Meloidogyne floridensis was first described in Florida, USA, in 2004 but has since been reported in California, South Carolina, and Georgia. Our objective was to determine the galling and reproduction differences between two isolates of M. floridensis, Mf3 and MfGNV14, on culinary herbs. A duplicated study was performed where both isolates were inoculated separately to nine culinary herbs (basil, catnip, chicory, dill, fennel, marjoram, parsley, sage, and thyme). Tomato was used as a susceptible reference. Regardless of the isolate, chicory and marjoram had the lowest gall indices (1.85 and 1.00, respectively) and egg mass indices (1.25 and 0.90, respectively). The reproduction rate of Mf3 was greatest under catnip (959 eggs/g fresh root) and thyme (701 eggs/g fresh root), followed by sage (549 eggs/g fresh root) and parsley (501 eggs/g fresh root). Catnip (2,151 eggs/g fresh root) stood out for number of eggs among all tested herbs, followed by tomato (1,153 eggs/g fresh root) and sage (847 eggs/g fresh root) for MfGNV14. Marjoram was a non-host, chicory, fennel, and thyme were poor hosts, and catnip, parsley, and tomato were good hosts to both M. floridensis isolates. Basil, dill, and sage responses were isolate-specific, i.e., resistant to Mf3 but susceptible to MfGNV14.

Cyst nematodes of the genus Heterodera comprise 87 nominal species of economically important plant parasites, with the Avenae-group one of the largest, consisting of 12 species. Samplings for cyst nematode studies were carried out from multiple locations in Greece from 2013 to 2021. Cysts of the genus Heterodera were recovered from potato fields, athletic stadium turfgrass and a garlic field. The recovered populations were identified using sequences of 28S, ITS1 and ITS2 rRNA, mitochondrial COI, and nuclear Hsp90. Using integrative taxonomic approaches, the recovered isolates were identified as H. filipjevi (from potato fields and turfgrass), H. hordecalis (from potato fields) and H. mani (from a garlic field), representing new records for Greece. Population diversity within each species was investigated using statistical parsimony of ITS rRNA and mtCOI, revealing haplotypes of the Greek populations and their relationships to others found in the Mediterranean basin and worldwide.

Meloidogyne floridensis is a recently described species of root-knot nematode (RKN) that is very closely related to many other tropical RKN species, including M. incognita. Despite its close phylogenetic relationship, M. floridensis is distinctive from its close relatives in both its meiotic mechanism of reproduction and its documented virulence on many of the most common RKN resistance genes in cultivated peach, tomato, and pepper. To further characterize the virulence profile of M. floridensis, we conducted replicate screens using this nematode to infect a panel of pepper lines that carry different sets of known RKN resistance genes. We found that M. floridensis was virulent against all the most common RKN resistance genes, including N, Me1, and Me3. We also found that two of these lines, PA 136 and PM 217, were highly resistant to M. floridensis. PA136 was previously considered to be universally susceptible to all other RKN species. Further testing of an F1 hybrid of this line confirmed this result and indicated that PA 136 contains a yet uncharacterized and potentially dominant source of species-specific resistance against M. floridensis. These surprising results provide additional data on the differences between M. floridensis and its close relatives, and identify new sources of resistance that could be used by pepper breeding programs to develop new cultivars with resistance against this nematode.