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A new root-knot nematode (RKN) species, Meloidogyne karsseni n. sp., associated with sweet pepper from Mexico, and a population of M. paranaensis from Guatemala, are described using data from morphological, biochemical (isozyme enzymes), molecular, and phylogenetic analyses. Meloidogyne karsseni n. sp. can be morphologically diagnosed using the combined features of the second-stage juveniles, viz. body length (345 to 422 µm), a conical rounded head region, a post-labial annule lacking transverse striation, a thin stylet 11 to 12 µm long, rounded to oval and backwardly sloping knobs, dorsal gland orifice (DGO) at 5.2 to 6.0 µm from the knobs, a hemizonid just above the secretory-excretory (SE) pore, a tapering tail with finely rounded terminus and one or two very weak constrictions at hyaline tail tip; the female characters viz. oval-to-rounded perineal pattern with coarse striation on lateral sides around the anus, low dorsal arch with finer striations, and distinctly visible lateral lines; and the male characteristics viz. a rounded and continuous head, a post-labial annule without transverse striations, a robust stylet 20 to 24 µm long, rounded-to-oval and slightly backwardly sloping knobs, and a DGO at 2.4 to 2.9 µm from the knobs. In all the studied males of M. paranaensis, a characteristic sclerotization around the duct of SE-pore was also observed for the first time. Sequences of 18S, D2-D3 of 28S, and ITS of rDNA, and cox1 of mtDNA were generated for the two species, and in the phylogenetic trees based on these genes, both species appeared in the tropical RKN species complex clade.

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Five species of root-knot nematodes (RKN), Meloidogyne spp. (M. haplanaria, M. incognita, M. floridensis, M. javanica, and M. arenaria) were detected in 67% of vegetable-growing regions in Georgia, United States (Marquez et al. 2021a, b; Marquez and Hajihassani 2022a, b). In October 2021, two sweet potato (Ipomoea batatas) samples (FF1 and FF2) collected at harvest from a field located in Tattnall County, Reidsville, GA were received for assessment. Symptoms of RKN damage on storage roots included a veiny appearance, surface cracking, and bumpy yellow to brown colored specks (Fig. 1). The population density of RKN second-stage juveniles (J2) was 148 and 180 J2/100 cm3 of soil for FF1 and FF2 samples, respectively. Genomic DNA was isolated by smashing females (n=10) individually in 20 µL of PCR-grade water, followed by freezing at -20°C overnight and thawing at 95°C for 1 min. Each DNA sample was first analyzed with a duplex PCR method using RKN species-specific primer sets for the most common nematode species: Mi2F4/Mi1R1 (M. incognita) and Far/Rar (M. arenaria) and SEC-1F/SEC-1R (M. incognita) and Fjav/Rjav (M. javanica) (Zijlstra et al. 2000; Hajihassani et al. 2022). Since this method failed to identify the RKN species, DNA samples were amplified with Me-F and Me-R primers, specific for diagnosing M. enterolobii (Long et al. 2006). Species-specific PCR produced a 240 bp DNA fragment for FF1 and FF2 samples (Fig. 2), corresponding to M. enterolobii. RKN species identification was confirmed by DNA sequencing using C2F3/1108 and TRNAH/MRH106 primers (Powers et al. 2018; Stanton et al. 1997). Products of C2F3/1108 (GenBank accessions ON320401 and ON320405) were 100% identical with 100% query coverage to a North Carolina M. enterolobii isolate (MN809527), while TRNAH/MHR106 sequences (ON320402 and ON320406) was 99.4-99.8% identical with 89-91% query coverage to a China isolate (MF467278). Measurements [Mean (range)] of body length of M. enterolobii J2 (BL): 454.0 (411.3-485.1) µm; maximum body width (BW): 15.1 (13.8-17.0) µm; stylet length: 14.3 (12.7-15.2) µm; total BL/greatest BW: 30.1 (28.6-31.4) µm; and BL/head end to posterior end of metacorpus: 7.3 (6.5-8.2) µm. Morphological measurements of J2 were comparable to the original description of M. enterolobii Yang and Eisenback. The host suitability of sweet potato varieties [Covington (susceptible to M. enterolobii), Beauregard (susceptible to intermediate), and Regal (resistant)] to the M. enterolobii isolate was assessed (Rutter et al. 2021). Nematode eggs were extracted from skin/bumps of samples FF1 and FF2 by blending (15 sec) and shaking in a 0.5% NaOCl solution (5 min), followed by washing and centrifugation in a standard sucrose solution. Sweet potato slips were transplanted in 10.8-cm-diam. pots filled with sand and steamed field soil (1:1 v/v), and two days after planting, were inoculated with 10,000 eggs of M. enterolobii (six replicates per plant variety). Plants were maintained in a greenhouse at 25-28°C for 85 days in a completely randomized design. Root galling index (scale of 0 to 5) of 4.4, 4.2, and 0.8 (Fig. 3) and reproduction factor (final egg numbers/initial egg number) of 8.2, 7.5, and 0.01 were obtained for Covington, Beauregard, and Regal, respectively confirming that Covington and Beauregard are susceptible to M. enterolobii while Regal is resistant. Meloidogyne enterolobii has not been reported in GA and this is the first report of the nematode on sweet potato in the state. This RKN species is an emerging pest of economic importance in many crops in the Southern United States (Brito et al. 2004; Rutter et al. 2018; Ye et al. 2013). Development of effective short- and long-term control procedures is urgently needed for managing M. enterolobii.

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Southern blight, caused by the soilborne fungus Athelia rolfsii, has increased in frequency and severity in the southern United States since the use of methyl bromide fumigation ceased. The objective of this study was to evaluate three cultivars of sticky nightshade (Solanum sisymbriifolium), previously used as tomato rootstocks because of resistance to root-knot nematode, for resistance to southern blight. Field experiments in infested soil were done in Georgia in 2020 and 2021 and in South Carolina in 2021. Tomato cultivar Roadster was used as the scion. Control treatments included nongrafted 'Roadster' in all experiments and self-grafted 'Roadster' in Georgia. In all three experiments, all rootstocks significantly reduced incidence of southern blight and increased vigor ratings compared to control treatments (P ≤ 0.007). The rootstocks Maxifort, White Star, and SisSyn II, but not Diamond, significantly increased marketable weight (P ≤ 0.02) and crop value (P < 0.05) compared to control treatments. In South Carolina only, because of greater yields than in Georgia, net returns with Maxifort and White Star were significantly greater than net return with nongrafted 'Roadster' (P = 0.004). When the wholesale price for fresh market tomato is ≥$13/box, grafting may be an effective and economical management for southern blight.

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BACKGROUND: Cover crops can suppress soilborne nematodes and fungal pathogens by serving as a poor host to pathogens and producing allelopathic compounds. Yet, cultural practices can influence their effectiveness. Cover crop and weedy fallow rotations and their interactions with deep tillage were evaluated from 2019 to 2021 in a three-season vegetable cropping system (spring tomato, fall squash, and winter cabbage) for their suppressive effects on soilborne diseases. Experimental plots were arranged in a split-plot 2 × 4 factorial design in randomized complete blocks. Whole-plot tillage treatments were shallow-tilled or deep-tilled. Subplots had two factors of crop rotations: rotation type (cover crop [spring or fall sunn hemp or winter rye] or weedy fallow) and rotation season. RESULTS: Independent of tillage practice, sunn hemp and weedy fallow reduced population density and root galling severity of root-knot nematode (Meloidogyne incognita) for the first subsequent vegetable compared to the all-vegetable rotation (P < 0.05) but had little effect on fungal pathogens. Fall sunn hemp had higher plant biomass and reduced gall severity for the second subsequent vegetable. Spring and fall sunn hemp improved vegetable yields. Winter rye only reduced ring nematodes (Mesocriconema spp.) population density in the first subsequent vegetable. Deep tillage reduced incidence of fungal pathogens of Rhizoctonia solani and Sclerotinia sclerotiorum, and population density of stubby-root nematode (Nanidorus minor). CONCLUSION: Sunn hemp is effective in suppressing M. incognita, whereas deep tillage can be used to suppress R. solani, S. sclerotiorum, and N. minor in vegetable production systems. © 2023 Society of Chemical Industry.

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Meloidogyne floridensis is of particular concern because it reproduces on tomato, pepper, corn, and tobacco cultivars that have resistance to the common tropical root-knot nematode (RKN) species (i.e., Meloidogyne incognita, M. arenaria, and M. javanica). During a survey of 436 randomly selected vegetable fields in Georgia in 2018, 6 M. floridensis-infested fields were found and cultured from single egg-mass isolates on a susceptible tomato (cultivar Rutgers), and speciated using molecular analyses. Five isolates of M. floridensis were identified from collard, cowpea, cucumber, watermelon, and tomato fields by DNA sequence-based identification targeting mitochondrial genes (cytochrome c oxidase subunit II, transfer RNAHis, large subunit ribosomal RNA, and NADH dehydrogenase subunit 5). Two greenhouse trials determined the host preference and reproduction level for each M. floridensis isolate. Evaluations were conducted on Rutgers tomato, a resistant tomato (cultivar Skyway, carrying the Mi-1.2 gene), and vegetable crops associated with the origin of M. floridensis populations. This study confirmed that most associated vegetables, except collards, were good hosts to M. floridensis, having a reproduction factor >1. All isolates were able to reproduce aggressively on the resistant tomato. We found variations among M. floridensis isolates in pathogenicity and reproduction levels on the vegetable crops tested which should be considered when using or developing host resistance.

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Root-knot nematode (RKN; Meloidogyne spp.) is the most prevalent plant-parasitic nematode in vegetable fields of Georgia, with an incidence of 67.3%. Because aggressive RKN species are reported in the southeastern United States, molecular-based identification of RKN species was conducted on soil samples taken from a nematode surveillance study in 2018 from 292 RKN-infested vegetable fields in southern Georgia. The RKN-infested soil was potted with tomato cultivar Rutgers, and individual nematode females were isolated from galled roots and subjected to species-specific PCR and mitochondrial haplotype-based RKN species identification. The incidence (%), mean, and maximum relative abundance (second-stage juveniles per 100 cm3 of soil) of the five RKN species identified consisted of M. incognita (91.9, 486, 14,144), M. arenaria (36.0, 707, 14,144), M. floridensis (2.2, 909, 5,264), M. javanica (5.5, 352, 1,488), and M. haplanaria (0.7, 8, 14). A large proportion of fields (29%) had mixed populations of M. incognita and M. arenaria, which may reflect the region's long history of cotton and peanut cultivation. For unknown reasons, mixed populations of M. incognita and M. arenaria were associated with higher population densities. M. incognita is the most important RKN species in vegetable fields, followed by M. arenaria; therefore, pure or mixed populations of these species should be addressed in nematode management programs. Although at a lower incidence, the newly detected species, M. floridensis and M. haplanaria, have the potential to become a major threat since they reproduce on vegetables with Mi-resistant genes.

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The soil-borne pathogens, particularly Fusarium oxysporum f. sp. niveum (FON) and southern root-knot nematode (RKN, Meloidogyne incognita) are the major threats to watermelon production in the southeastern United States. The role of soil micronutrients on induced resistance (IR) to plant diseases is well-documented in soil-based media. However, soil-based media do not allow us to determine the contribution of individual micronutrients in the induction of IR. In this manuscript, we utilized hydroponics-medium to assess the effect of controlled application of micronutrients, including iron (Fe), manganese (Mn), and zinc (Zn) on the expression of important IR genes (PR1, PR5, and NPR1 from salicylic acid (SA) pathway, and VSP, PDF, and LOX genes from jasmonic acid (JA) pathway) in watermelon seedlings upon inoculation with either FON or RKN or both. A subset of micronutrient-treated plants was inoculated (on the eighth day of micronutrient application) with FON and RKN (single or mixed inoculation). The expression of the IR genes in treated and control samples was evaluated using qRT-PCR. Although, significant phenotypic differences were not observed with respect to the severity of wilt symptoms or RKN galling with any of the micronutrient treatments within the 30-day experimental period, differences in the induction of IR genes were considerably noticeable. However, the level of gene expression varied with sampling period, type and concentration of micronutrients applied, and pathogen inoculation. In the absence of pathogens, micronutrient applications on the seventh day, in general, downregulated the expression of the majority of the IR genes. However, pathogen inoculation preferentially either up- or down-regulated the expression levels of the IR genes at three days post-inoculation depending on the type and concentration of micronutrients. The results demonstrated here indicate that micronutrients in watermelon may potentially make watermelon plants susceptible to infection by FON and RKN. However, upon infection the IR genes are significantly up-regulated that they may potentially aid the prevention of further infection via SA- and JA-pathways. This is the first demonstration of the impact of micronutrients affecting IR in watermelon against FON and RKN infection.

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Meloidogyne incognita, the southern root-knot nematode (RKN), is the most predominant plant-parasitic nematode species of tomato and causes significant yield loss. The Mi-1.2 gene confers resistance in tomatoes to M. incognita; however, virulent RKN populations capable of parasitizing resistant tomato cultivars have been reported from different regions in the world. Four naturally occurring virulent populations of M. incognita were found in vegetable fields from four counties in Georgia with no history of tomato cultivation of the Mi gene. Two consecutive greenhouse trials showed that all four virulent RKN populations reproduced on tomato cultivars, including Amelia, Skyway, and Myrtle, with the Mi-1 gene, while an avirulent population of M. incognita race 3 was unable to overcome host resistance. Virulent RKN populations varied in reproduction among resistant cultivars, with Ma6 population having the greatest reproduction potential. No difference in penetration potential of the virulent (Ma6) and avirulent populations was found on susceptible and resistant tomato cultivars. However, virulent Ma6 population females were successful at egg-laying, whereas avirulent female development was arrested in the resistant cultivars. The virulent Ma6 population also induced feeding sites in the roots of resistant cultivars, whereas the avirulent population did not. To our knowledge, this is the first report of resistance-breaking populations of M. incognita in Georgia and the second state in the United States after California.

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We profiled the global gene expression landscape across the reproductive lifecycle of Brassica napus. Comparative analysis of this nascent amphidiploid revealed the contribution of each subgenome to plant reproduction. Whole-genome transcription factor networks identified BZIP11 as a transcriptional regulator of early B. napus seed development. Knockdown of BZIP11 using RNA interference resulted in a similar reduction in gene activity of predicted gene targets, and a reproductive-lethal phenotype. Global mRNA profiling revealed lower accumulation of Cn subgenome transcripts relative to the An subgenome. Subgenome-specific transcription factor networks identified distinct transcription factor families enriched in each of the An and Cn subgenomes early in seed development. Analysis of laser-microdissected seed subregions further reveal subgenome expression dynamics in the embryo, endosperm and seed coat of early stage seeds. Transcription factors predicted to be regulators encoded by the An subgenome are expressed primarily in the seed coat, whereas regulators encoded by the Cn subgenome were expressed primarily in the embryo. Data suggest subgenome bias are characteristic features of the B. napus seed throughout development, and that such bias might not be universal across the embryo, endosperm and seed coat of the developing seed. Transcriptional networks spanning both the An and Cn genomes of the whole B. napus seed can identify valuable targets for seed development research and that -omics level approaches to studying gene regulation in B. napus can benefit from both broad and high-resolution analyses.

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Zinc (Zn) accumulation and deficiency affect plant response to pests and diseases differently in varying pathosystems. The concentrations of Zn in plants aid in priming defense signaling pathways and help in enhanced structural defenses against plant pathogens. Studies are lacking on how concentrations of Zn in watermelon plants influence defense against two important soil-borne pathogens: Fusarium oxysporum f. sp. niveum (FON) and southern root-knot nematode (RKN, Meloidogyne incognita). In this study a comparative transcriptomics evaluation of watermelon plants in response to high (1.2 ppm) and low (0.2 ppm) levels of Zn were determined. Differential transcript-level responses differed in watermelon plants when infected with FON or RKN or both under high- and low-Zn treatment regimes in a controlled hydroponics system. Higher numbers of differentially expressed genes (DEGs) were observed in high-Zn-treated than in low-Zn-treated non-inoculated plants, in plants inoculated with FON alone and in plants inoculated with RKN alone. However, in the co-inoculated system, low-Zn treatment had higher DEGs as compared to high-Zn treatment. In addition, most DEGs were significantly enriched in hormone signal transduction and MAPK signaling pathway, suggesting an induction of systemic resistance with high-Zn concentrations. Taken together, this study substantially expands transcriptome data resources and suggests a molecular potential framework for watermelon-Zn interaction in FON and RKN.

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Plant-parasitic nematodes (PPN) limit yields of vegetable production in the United States. During the spring and fall cropping seasons of 2018, 436 fields in bare ground and plastic bed cropping systems were randomly sampled from 29 counties in southern Georgia. The incidence (%), mean relative abundance, and maximum relative abundance (nematodes per 100 cm3 of soil) of the 10 different PPN genera detected in 32 vegetable crops in bare ground and plastic bed cropping systems include Meloidogyne spp. (67.3%; mean, 292; maximum, 14,144), Nanidorus spp. (49.4%; mean, 6; maximum, 136), Mesocriconema spp. (39.6%; mean, 17; maximum, 340), Helicotylenchus spp. (31.6%; mean, 20; maximum, 1152), Pratylenchus spp. (20.1%; mean, 2; maximum, 398), Rotylenchulus spp. (5.9%; mean, 1; maximum, 116), Hoplolaimus spp. (12.6%; mean, 1; maximum, 78), Heterodera spp. (2.3%; mean, <1; maximum, 60), Tylenchorhynchus spp. (0.9%; mean, <1; maximum, 12), and Xiphinema spp. (0.2%; mean, <1; maximum, 2). A nonmetric multidimensional scaling analysis indicated that most environmental and geological factors (i.e., longitude, precipitation, soil moisture, sand and silt content, and soil electrical conductivity) had no apparent relationship with nematode counts, except for latitude, soil pH, and temperature. The multirank permutation procedure followed by indicator species analysis and nonparametric Kruskal-Wallis analysis of variance indicated that Meloidogyne spp. are the predominant PPN associated with plastic beds in the south region sampled. The south region consisted mainly of commercial fields that rotated multiple vegetables crops through the same plastic beds. All other PPNs were associated with bare ground beds in the north region that are commonly rotated with row crops. This study validates that Meloidogyne spp. are the most important PPN in vegetable fields of southern Georgia and suggests that cropping systems have a greater effect on PPN population dynamics than the environment.

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Meloidogyne floridensis, also known as the peach root-knot nematode (RKN), is a new emerging species found to break crop host-resistance to M. incognita (Stanley et al. 2009). It was first described from Florida (Handoo et al. 2004) parasitizing M. incognita-resistant rootstock cultivars of peach (Prunus persica), and tomato (Solanum lycopersicum) (Church 2005). The nematode has recently been reported in California's almond orchards (Westphal et al. 2019) and peach rootstock (cv. Guardian) in South Carolina (Reighard et al. 2019). In a 2018 survey of vegetable fields sampled randomly in South Georgia, RKN was found with a high density (5,264 second-stage juveniles (J2)/100 cm3 of soil) from a tomato field in Ware County, GA. The soil sample consist of 30 soil cores sampled at 20-cm depth across the field in a zig-zag motion. To perform Koch's postulate, 2,000 eggs from a single egg-mass culture were inoculated into deepots filled with mixture of sand and sterilized field soil (1:1 v/v) and grown with tomato cv. Rutgers for 60 days in the greenhouse. A reproduction factor of 21.1 ± 6.1 was obtained confirming the nematode parasitism on tomato (Fig. 1S). For molecular identification, DNA was extracted by smashing three individual females isolated from the galled roots in 50 µl sterile distilled water, followed by a freeze-thaw (95°C, 1 min). Results of PCR analyzes by species-specific primers (Fjav/Rjav, Finc/Rinc and Far/Rar) did not detect the nematode species (Zijlstra et al. 2000). PCR products were obtained and sequenced from two primer sets consisting of the forward NAD5F2 (5'-TATTTTTTGTTTGAGATATATTAG-3') and the reverse NAD5R1 (5'-CGTGAATCTTGATTTTCCATTTTT-3') for amplification of a fragment of the NADH dehydrogenase subunit 5 (NADH5) gene (Janssen et al. 2016), and the forward TRANH (5'-TGAATTTTTTATTGTGATTAA-3') and the reverse MRH106 (5'-AATTTCTAAAGACTTTTCTTAGT-3') for amplification covering a portion of the cytochrome c oxidase subunit II (COII) and large subunit 16SrDNA (16S) gene (Stanton et al. 1997). DNA sequence of NADH5 gene fragment (accession no. MT795954) was 100% identical (532/532 bp) with a M. floridensis isolate from California and South Carolina (accession no. MH729181 and MN072363), while fragment of the COII and 16S genes (accession no. MT787563) was 99.76% identical (421/422 bp) with an isolate from Florida (accession no. DQ228697). The nematode females were also used for morphometric and perennial pattern analysis. Several micrographs with the inverted microscope (ZEISS Axio Vert.A1, Germany) and camera (ZEISS Axiocam 305 color, Germany) were taken from ten J2s for mean, standard deviation and range of body length: 362.7 ± 11.2 (340.4-379) µm, maximum body width: 15 ± 1.3 (12.4-16.4) µm, stylet length: 12.3 ± 1.3 (9.5-14) µm, hyaline tail terminus: 8.9 ± 1.1 (7.5-10.9) µm and tail length: 35.7 ± 4.4 (28.5-39.5) µm. Morphological measurements and configuration of perineal patterns (Fig. 2S) were comparable to previous reports of M. floridensis isolates from Florida (Handoo et al. 2004; Stanley et al. 2009). To the best of our knowledge, this is the first report of M. floridensis in Georgia as the fourth state in the USA after South Carolina, California and Florida. This nematode has been reported to parasitize several vegetable crops, including cucumber, eggplant, tomato, snap bean and squash. Furthermore, RKN resistant cultivars of tomato (harboring Mi-1 gene), pepper (harboring N gene), corn cv. Mp-710 and tobacco cv. NC 95 have been found susceptible to M. floridensis (Stanley et al. 2009), making it a serious threat.

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Root-knot nematodes (RKNs), Meloidogyne spp., are sedentary endoparasites that negatively affect almost every crop in the world. Current management practices are not enough to completely control RKN. Application of certain chemicals is also being further limited in recent years. It is therefore crucial to develop additional control strategies through the application of environmentally benign methods. There has been much research performed around the world on the topic, leading to useful outcomes and interesting findings capable of improving farmers' income. It is important to have dependable resources gathering the data produced to facilitate future research. This review discusses recent findings on the application of environmentally benign treatments to control RKN between 2015 and April 2020. A variety of biological control strategies, natural compounds, soil amendments and other emerging strategies have been included, among which, many showed promising results in RKN control in vitro and/or in vivo. Development of these methods continues to be an area of active research, and new information on their efficacy will continuously become available. We have discussed some of the control mechanisms involved and suggestions were given on maximizing the outcome of the future efforts.

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Meloidogyne partityla is the dominant root-knot nematode (RKN) species parasitizing pecan in Georgia. This species is known to cause a reduction in root growth and a decline in the yields of mature pecan trees. Rapid and accurate diagnosis of this RKN is required to control this nematode disease and reduce losses in pecan production. In this study, a loop-mediated isothermal amplification (LAMP) method was developed for simple, rapid, and on-site detection of M. partityla in infested plant roots and validated to detect the nematode in laboratory and field conditions. Specific primers were designed based on the sequence distinction of the internal transcribed spacer (ITS)-18S/5.8S ribosomal RNA gene between M. partityla and other Meloidogyne spp. The LAMP detection technique could detect the presence of M. partityla genomic DNA at a concentration as low as 1 pg, and no cross reactivity was found with DNA from other major RKN species such as M. javanica, M. incognita and M. arenaria, and M. hapla. We also conducted a traditional morphology-based diagnostic assay and conventional polymerase chain reaction (PCR) assay to determine which of these techniques was less time consuming, more sensitive, and convenient to use in the field. The LAMP assay provided more rapid results, amplifying the target nematode species in less than 60 min at 70°C, with results 100 times more sensitive than conventional PCR (~2-3 hrs). Morphology-based, traditional diagnosis was highly time-consuming (2 days) and more laborious than conventional PCR and LAMP assays. These features greatly simplified the operating procedure and made the assay a powerful tool for rapid, on-site detection of pecan RKN, M. partityla. The developed LAMP assay will facilitate accurate pecan nematode diagnosis in the field and contribute to the management of the pathogen.

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Oilseed radish and oat are cool season annual crops that are potentially used as "trap" or "biofumigant" crops for the suppression of plant-parasitic nematodes in soil. Cultivars of oilseed radish (Carwoodi, Cardinal, Final, Image, Concorde, Control, Eco-Till, Karakter and Cannavaro), white (Tachiibuki) and black (Pratex) oats were evaluated for their ability to reduce reproduction of three root-knot nematode species: Meloidogyne javanica, M. incognita race 3, and M. arenaria race 1. Nematode penetration and development were also evaluated using selected resistant and susceptible cultivars under greenhouse conditions. Root galling severity, number of eggs per gram of fresh root, and rate of reproduction varied among the cultivars in response to nematode infection. Oilseed radish cv. Carwoodi was resistant to M. javanica, whereas Karakter and Concorde were maintenance hosts allowing the nematode to maintain or increase its population on the plants. For M. incognita, Control and Carwoodi oilseed radish and Tachiibuki oat were resistant hosts. The cultivars that supported little reproduction of M. arenaria were Karakter and Carwoodi radish, and Tachiibuki oat. Comparable numbers of nematodes entered the roots of susceptible and resistant cultivars of oilseed radish and oat during early stages of infection. However, the development of the nematodes as evident from counting young and egg-laying females in roots were significantly decreased or inhibited in the resistant cultivars compared to the susceptible cultivars indicating that resistance occurs at post-infection stages. Histopathological examinations of galled-root tissues also revealed the susceptibility and resistance responses of selected cultivars of oilseed radish and oat to these nematode species.Oilseed radish and oat are cool season annual crops that are potentially used as "trap" or "biofumigant" crops for the suppression of plant-parasitic nematodes in soil. Cultivars of oilseed radish (Carwoodi, Cardinal, Final, Image, Concorde, Control, Eco-Till, Karakter and Cannavaro), white (Tachiibuki) and black (Pratex) oats were evaluated for their ability to reduce reproduction of three root-knot nematode species: Meloidogyne javanica, M. incognita race 3, and M. arenaria race 1. Nematode penetration and development were also evaluated using selected resistant and susceptible cultivars under greenhouse conditions. Root galling severity, number of eggs per gram of fresh root, and rate of reproduction varied among the cultivars in response to nematode infection. Oilseed radish cv. Carwoodi was resistant to M. javanica, whereas Karakter and Concorde were maintenance hosts allowing the nematode to maintain or increase its population on the plants. For M. incognita, Control and Carwoodi oilseed radish and Tachiibuki oat were resistant hosts. The cultivars that supported little reproduction of M. arenaria were Karakter and Carwoodi radish, and Tachiibuki oat. Comparable numbers of nematodes entered the roots of susceptible and resistant cultivars of oilseed radish and oat during early stages of infection. However, the development of the nematodes as evident from counting young and egg-laying females in roots were significantly decreased or inhibited in the resistant cultivars compared to the susceptible cultivars indicating that resistance occurs at post-infection stages. Histopathological examinations of galled-root tissues also revealed the susceptibility and resistance responses of selected cultivars of oilseed radish and oat to these nematode species.

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Root-knot nematodes (Meloidogyne spp.) are important contributors to yield reduction in tomato. Though resistant cultivars to common species (Meloidogyne arenaria, M. incognita, and M. javanica) are available, they are not effective against other major species of root-knot nematodes. Cultivars or lines of Solanum sisymbriifolium were examined to assess the presence and level of resistance to five major species: M. arenaria race 1, M. incognita race 3, M. haplanaria, M. javanica, and M. enterolobii. Differences in S. sisymbriifolium response to the nematode infection were apparent when susceptibility or resistance was classified by the egg counts per gram fresh weight of root and the multiplication rate of the nematodes. The cultivar Diamond was highly susceptible, Quattro and White Star were susceptible, while Sis Syn II was resistant to M. arenaria. Quattro, White Star, and Sis Syn II exhibited a moderate to high level of resistance to M. incognita but the nematode increased 2.5-fold from the initial population of the M. incognita on Diamond. All S. sisymbriifolium cultivars were highly resistant to both M. haplanaria and M. enterolobii, while highly susceptible to M. javanica. A microplot study under field conditions using Sis Syn II confirmed that M. arenaria, M. incognita, and M. haplanaria were not pathogenic on the plant. Likewise, an examination on cross-sections of galled root tissues confirmed the susceptibility and resistance of S. sisymbriifolium lines to Meloidogyne spp. Using S. sisymbriifolium as a resistant rootstock or a new source of resistance may result in the development of nonchemical and sustainable management strategies to protect the tomato crop.

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We found that Nanidorus spp. was pathogenic to seashore paspalum (Paspalum vaginatum) turfgrass as its population increased from 100 to 2,080 nematodes per pot 180 days after inoculation under greenhouse conditions. Morphological measurements of adult females were similar to those described for N. minor. Molecular analysis also confirmed the morphological identification by targeting three different regions of the genomic DNA. Three primer pairs targeting 18S rDNA (360F/932R), 28S rDNA (D2A/D3B) and ITS1 rDNA (BL18/5818) were used in singleplex PCR. Forward and reverse sequences of each individual primer set were then subjected to multiple alignment and the complimentary sequences were assembled into a consensus sequence. Upon nucleotide blast on the NCBI website, they were all confirmed to be N. minor. A one-step multiplex PCR method using specific primers and a fragment size of 190 bp also confirmed the identity of N. minor. To the best of our knowledge, this is the first report of N. minor infecting seashore paspalum turfgrass in Georgia.

RESUMEN

The southern root-knot nematode (RKN), Meloidogyne incognita, is particularly difficult to manage because of high susceptibility of all commercial cucumber (Cucumis sativus) cultivars to this nematode. Growers have conventionally relied on nematicide applications to control RKN. Two microplot experiments were conducted in which four nonfumigant nematicides, oxamyl, fluopyram, fluensulfone, and fluazaindolizine, were examined for their efficacy in reducing gall severity and postharvest soil nematode numbers in microplots inoculated with increasing inoculation densities (1,000, 5,000, 10,000, and 20,000 nematodes/microplot), and improving growth and yield of cucumber. Nematicides were applied 1 day prior to transplanting cucumber seedlings, except fluensulfone, which was applied 7 days before transplanting. At harvest, root gall indices differed significantly (P < 0.0001) among nematode inoculation densities and nematicides. All four nematicides were effective in reducing the root gall index when compared with the untreated control on a consistent basis at all M. incognita inoculation densities. At the lowest inoculation density, no significant difference in gall index or final population density was observed among nematicides; however, gall index increased with increasing nematode inoculation densities in nematicide-treated microplots. Correlations between gall index and inoculation density clearly showed that soil treatment with fluensulfone, fluazaindolizine, or fluopyram was more effective in reducing gall severity than treatment with oxamyl. Regression analysis also indicated no significant effect of nematode inoculation densities on yield of cucumber treated with these nematicides. Results of this study will provide guidance for improving nematicide efficiencies in soil with varying inoculation densities of RKN.

Asunto(s)

RESUMEN

Ginger (Zingiber officinale L.) and turmeric (Curcuma longa L.) are two her baceous perennial plant species with rhizomes that are commonly used for flavoring or medicinal purposes. In January 2018, stunting and poorly developed root systems typically associated with plant-parasitic nematode infection were observed on organically grown edible ginger and turmeric in a hoop house in Wheeler County, Georgia. Examination of soil and root samples from symptomatic plants revealed the presence of high populations of root-knot nematodes (Meloidogyne spp.). The second-stage juveniles (J2s) were extracted from soil samples as described by Jenkins (1964). Nematode counts were 285 and 155 J2s per 100 cm3 soil in the areas planted with ginger and turmeric, respectively. Nematode eggs were recovered from infected root systems using the bleach (1%) and blending method (Hussey and Barker, 1973). Examination of the root samples showed the presence of 840 and 320 eggs per g of roots in ginger and turmeric, respectively. Primary diagnosis of the Meloidogyne specimens was done by comparing morphological features observed in the J2s (n = 10) and perineal pattern of females (n = 11) based on the description given by Eisenback and Triantaphyllou (1991) and were tentatively identified as M. javanica (Treub, 1885; Chitwood, 1949). For species identification, DNA sequencing was performed using multiple markers located in 18S ribosomal RNA and 5.8S internal transcribed spacer 1 regions, (18S + ITS) (GenBank Accession No. MK390613), 28S domain 2 and 3 (28S D2/D3) (MK385596), cytochrome oxidase subunit I (COI) (MK391558), and subunit II and 16S (COII + 16S) (MK391557) of mitochondrial DNA following methods as described in Ye et al. (2015). PCR assays by species-specific primers were also conducted to confirm species identity as described by Zijlstra et al. (2000). The blast search results of DNA sequences of 18S + ITS, 28S (D2/D3), COI and COII + 16S revealed the best match as M. javanica, M. incognita (Kofoid and White, 1912; Chitwood, 1949) and M. arenaria (Neal, 1889; Chitwood, 1949) with 99-100% identity. These genes are highly conserved across these three most common root-knot nematode species. However, results of PCR assays by species-specific primers were only positive for M. javanica using primers Fjav/Rjav, but negative for M. incognita by Finc/Rinc and M. arenaria by Far/Rar as described by Zijlstra et al. (2000). Based on morphological characteristics and molecular analyses, the root-knot nematodes infecting ginger and turmeric were identified as M. javanica. After confirmation of the nematode species, a test was conducted in the greenhouse to assess the pathogenicity of the nematode on ginger and turmeric. Five seedlings per plant species (cultivars unknown) were grown in 15 cm-diam plastic pots containing equal parts of pasteurized field soil and sand, and then inoculated with 2,000 eggs of M. javanica. The egg suspension was added into three holes around the base of each seedling. Non-inoculated seedlings (n2 = 25) were used as controls. Plants were arranged in completely randomized design and grown at 25 ± 3 °C for 10 weeks. At the termination of the experiment, small galls were noticed on the roots of the inoculated seedlings of both ginger and turmeric. No galls were observed on the roots of non-inoculated plants. Egg were extracted from the galled roots (Hussey and Barker, 1973) yielding an average of 1040 ± 96 and 732 ± 54 eggs per g of root of ginger and turmeric, respectively. On ginger, the nematode produced large numbers of galls and egg masses on both primary and secondary (feeder) roots, but the galls produced on turmeric were often observed only on primary roots (Fig. 1). No symptoms of root-knot nematode infestation including galls or water-soaked lesions were observed on the outer surface of rhizomes of both ginger and turmeric. However, the size of rhizomes in the M. javanica-infested areas was visibly smaller than that in non-infested areas (Fig. 2). A similar reduction in the growth of turmeric rhizomes was also observed. Meloidogyne incognita has been commonly reported as a nematode pest of ginger (Myers et al., 2017) and turmeric (Hall et al., 2017) in the USA and both M. incognita and M. javanica are known to cause damage on these plant hosts (Ray et al., 1995; Singh and Gupta, 2011). To the best of our knowledge, this is the first report of M. javanica on ginger and turmeric in the USA.Ginger (Zingiber officinale L.) and turmeric (Curcuma longa L.) are two her baceous perennial plant species with rhizomes that are commonly used for flavoring or medicinal purposes. In January 2018, stunting and poorly developed root systems typically associated with plant-parasitic nematode infection were observed on organically grown edible ginger and turmeric in a hoop house in Wheeler County, Georgia. Examination of soil and root samples from symptomatic plants revealed the presence of high populations of root-knot nematodes (Meloidogyne spp.). The second-stage juveniles (J2s) were extracted from soil samples as described by Jenkins (1964). Nematode counts were 285 and 155 J2s per 100 cm3 soil in the areas planted with ginger and turmeric, respectively. Nematode eggs were recovered from infected root systems using the bleach (1%) and blending method (Hussey and Barker, 1973). Examination of the root samples showed the presence of 840 and 320 eggs per g of roots in ginger and turmeric, respectively. Primary diagnosis of the Meloidogyne specimens was done by comparing morphological features observed in the J2s (n = 10) and perineal pattern of females (n = 11) based on the description given by Eisenback and Triantaphyllou (1991) and were tentatively identified as M. javanica (Treub, 1885; Chitwood, 1949). For species identification, DNA sequencing was performed using multiple markers located in 18S ribosomal RNA and 5.8S internal transcribed spacer 1 regions, (18S + ITS) (GenBank Accession No. MK390613), 28S domain 2 and 3 (28S D2/D3) (MK385596), cytochrome oxidase subunit I (COI) (MK391558), and subunit II and 16S (COII + 16S) (MK391557) of mitochondrial DNA following methods as described in Ye et al. (2015). PCR assays by species-specific primers were also conducted to confirm species identity as described by Zijlstra et al. (2000). The blast search results of DNA sequences of 18S + ITS, 28S (D2/D3), COI and COII + 16S revealed the best match as M. javanica, M. incognita (Kofoid and White, 1912; Chitwood, 1949) and M. arenaria (Neal, 1889; Chitwood, 1949) with 99­100% identity. These genes are highly conserved across these three most common root-knot nematode species. However, results of PCR assays by species-specific primers were only positive for M. javanica using primers Fjav/Rjav, but negative for M. incognita by Finc/Rinc and M. arenaria by Far/Rar as described by Zijlstra et al. (2000). Based on morphological characteristics and molecular analyses, the root-knot nematodes infecting ginger and turmeric were identified as M. javanica. After confirmation of the nematode species, a test was conducted in the greenhouse to assess the pathogenicity of the nematode on ginger and turmeric. Five seedlings per plant species (cultivars unknown) were grown in 15 cm-diam plastic pots containing equal parts of pasteurized field soil and sand, and then inoculated with 2,000 eggs of M. javanica. The egg suspension was added into three holes around the base of each seedling. Non-inoculated seedlings (n2 = 25) were used as controls. Plants were arranged in completely randomized design and grown at 25 ± 3 °C for 10 weeks. At the termination of the experiment, small galls were noticed on the roots of the inoculated seedlings of both ginger and turmeric. No galls were observed on the roots of non-inoculated plants. Egg were extracted from the galled roots (Hussey and Barker, 1973) yielding an average of 1040 ± 96 and 732 ± 54 eggs per g of root of ginger and turmeric, respectively. On ginger, the nematode produced large numbers of galls and egg masses on both primary and secondary (feeder) roots, but the galls produced on turmeric were often observed only on primary roots (Fig. 1). No symptoms of root-knot nematode infestation including galls or water-soaked lesions were observed on the outer surface of rhizomes of both ginger and turmeric. However, the size of rhizomes in the M. javanica-infested areas was visibly smaller than that in non-infested areas (Fig. 2). A similar reduction in the growth of turmeric rhizomes was also observed. Meloidogyne incognita has been commonly reported as a nematode pest of ginger (Myers et al., 2017) and turmeric (Hall et al., 2017) in the USA and both M. incognita and M. javanica are known to cause damage on these plant hosts (Ray et al., 1995; Singh and Gupta, 2011). To the best of our knowledge, this is the first report of M. javanica on ginger and turmeric in the USA.

RESUMEN

Root-knot nematode (Meloidogyne spp.) exhibits a substantial problem in pepper production, causing reduction in yield throughout the world. Continued assessment for root-knot resistance is important for developing new resistance cultivars. In this study, the effect of Me and N genes on the penetration and reproduction of M. incognita race 3, M. arenaria race 1, M. javanica, and M. haplanaria was examined under controlled greenhouse conditions using susceptible and resistant pepper lines/cultivars (Mellow Star, Yolo Wonder B, Charleston Belle, HDA-149, HDA-330, PM-217, and PM-687) differing in the presence or absence of resistant genes. The penetration and resistance responses of these pepper lines differed depending on the nematode species. More second-stage juveniles penetrated roots of susceptible control cultivar Mellow Star than roots of resistant cultivars/lines. Although, there was no significant difference in the nematode penetration among resistant lines 1 and 3 days after inoculation (DAI), variability in the penetration of M. incognita, M. javanica, and M. haplanaria was observed 5 DAI. This demonstrates the variability among different nematode resistance genes to invasion by Meloidogyne spp. Based on nematode gall index (GI) and reproduction factor (RF), Charleston Belle, HDA-149, PM-217 and PM-687 showed very high resistance (GI < 1 and RF < 0.1) to M. incognita, M. arenaria, and M. javanica. Although, all the Meloidogyne-resistant pepper lines evaluated were resistant to M. javanica and M. haplanaria, the susceptible cultivar Mellow Star was a good host for all nematode species having an RF ranging from 8.1 to 34.7. The N, Me1, and Me3 genes controlled resistance to reproduction of all species of Meloidogyne examined.Root-knot nematode (Meloidogyne spp.) exhibits a substantial problem in pepper production, causing reduction in yield throughout the world. Continued assessment for root-knot resistance is important for developing new resistance cultivars. In this study, the effect of Me and N genes on the penetration and reproduction of M. incognita race 3, M. arenaria race 1, M. javanica, and M. haplanaria was examined under controlled greenhouse conditions using susceptible and resistant pepper lines/cultivars (Mellow Star, Yolo Wonder B, Charleston Belle, HDA-149, HDA-330, PM-217, and PM-687) differing in the presence or absence of resistant genes. The penetration and resistance responses of these pepper lines differed depending on the nematode species. More second-stage juveniles penetrated roots of susceptible control cultivar Mellow Star than roots of resistant cultivars/lines. Although, there was no significant difference in the nematode penetration among resistant lines 1 and 3 days after inoculation (DAI), variability in the penetration of M. incognita, M. javanica, and M. haplanaria was observed 5 DAI. This demonstrates the variability among different nematode resistance genes to invasion by Meloidogyne spp. Based on nematode gall index (GI) and reproduction factor (RF), Charleston Belle, HDA-149, PM-217 and PM-687 showed very high resistance (GI < 1 and RF < 0.1) to M. incognita, M. arenaria, and M. javanica. Although, all the Meloidogyne-resistant pepper lines evaluated were resistant to M. javanica and M. haplanaria, the susceptible cultivar Mellow Star was a good host for all nematode species having an RF ranging from 8.1 to 34.7. The N, Me1, and Me3 genes controlled resistance to reproduction of all species of Meloidogyne examined.