Important Plant-parasitic Nematodes Research Articles

First report of cyst nematode (Heterodera elachista) on Zea mays in Gansu Province, China.

The cyst nematodes are important plant-parasitic nematodes and make detrimental economic impacts worldwide. Heterodera elachista attacks rice in Japan (Ohshima 1974), Iran (Tanha et al. 2004) and China (Ding et al. 2012) and also attacks corn in Italy (De Luca et al. 2013) and northeast China (Xiao et al. 2019). Considering this nematode can infect these two most important crops with high reproduction rates, special attention should be paid to avoid its spread to new areas by soil, water, and agricultural practices. A survey for cyst nematodes was performed in fields of corn seed for propagation in September 2018 in Zhangye City, Gansu Province, which is the biggest corn seed production base in China. One hundred seventy four samples were collected by the zig-zag method in about 25 ha corn fields. Each soil sample containing approximately 1 kg soil in total was from the mixture of 20 cores (20 cm in depth and 0.2 cm in diameter). Cysts were detected in 6 out of 174 samples using the sieving-decanting method (Byrd et al. 1983). The six samples from ~ 1.2 ha corn fields in which plants displayed symptoms of dwarf, yellow leaves and earlier wilting had an average of 14 ± 2.8 cysts per 100 g soil. The cysts (n = 30) were dark brown, spherical to lemon shape, protruding, tapered vulva with ambifenestrae separated by a vulva slit, obvious and medium-sized underbridge, few dark-brown vesicles and clear swollen protrusion around underbridge and cyst cuticle with a zigzag pattern. Morphological measurements of the cysts included body length (excluding neck) (range =359.4 to 498.6 μm, mean = 429.5 ± SD 39.3 μm), vulva slit length (34.3 to 42.8, 37.9 ± 2.5), fenestral length (31.2 to 43.8, 38.0 ± 4.4) and width (26.1 to 31.4, 29.3 ± 1.6), underbridge length (74.7 to 82.9, 78.3 ± 2.8). J2 (n = 20) had the following measurements: body length (386.6 to 454.9, 425.3 ± 21.8), stylet length (17.1 to 22.2, 19.2 ± 1.6), stylet knob width (3.4 to 4.3, 3.9 ± 0.3), tail length (50.5 to 60.5, 55.5 ± 3.3) and hyaline tail length (25.0 to 34.6, 29.1 ± 3.1). The morphological characteristics are consistent with the Italian population of H. elachista through the comparison of the measurements. DNA was extracted from a single cyst randomly chosen (n = 5) using the protocol described by Subbotin et al. (2001). The ITS-rDNA and D2/D3 fragments of the 28S rRNA were respectively amplified with universal primers pairs TW81 and AB28 (Subbotin et al. 2001) and D2A and D3B (Castillo et al. 2003), and sequenced (Tsingke Biological Technology, Beijing, China). The consensus ITS sequence (GenBank Accession No. MN699476, 1037 bp) had 98.37 to 99.60% similarity with the H. elachista from corn in Italy (KC618469) and in China (MH712504), and from rice in China (HM560778) and in Iran (AF498391). The D2/D3 sequence (GenBank Accession No. MN699477, 746 bp) exhibited 99.60 to 99.73% similarity with that of H. elachista from rice in China (JN202922, HM560842), and from corn in Italy (KC618462). This nematode population was identified as H. elachista according to the morphological and molecular features. Twenty-day-old corn seedling (cv. Tiannuo) was inoculated with 3000 J2 and eggs in a pot filled with sterile soil. Eight plants were inoculated and two uninoculated plants were used as controls. J2 were found in the stained roots at 10 d after inoculation and J4 were detected at 30 d. These inoculated plants exhibited yellowing and dwarfing similar to the symptoms observed initially in the field, and the control grew normally. After 60 d, the average of 28 cysts were detected from each inoculated plant. This is the first report of H. elachista in Gansu Province, northwest China.

Response of soybean cyst nematode (Heterodera glycines) and root-knot nematodes (Meloidogyne spp.) to gradients of pH and inorganic salts

Plant-parasitic nematodes are able to sense and respond to gradients of chemical signals. How pH and inorganic salts in the rhizosphere affect nematode accumulation and host-seeking is poorly understood. We investigate the response of different groups of plant-parasitic nematodes to pH and salt concentration gradients. Responses of infective juveniles (J2) of the economically important plant-parasitic nematodes, soybean cyst nematodes (SCN; Heterodera glycines) and root-knot nematodes (RKN; Meloidogyne incognita and M. hapla) to pH and salt gradients were assessed using Pluronic F-127 gel-based assays. Microelectrodes were utilized to measure pH and ion concentration gradients in the gel. Differences were found between the three nematode species in response to acid, base and salts. For SCN, maximum nematode accumulation was between pH range 4.98–5.46 in an acid gradient, while the preferred alkaline pH ranges were 8.40–8.78 and 9.52–9.99. The preferred Cl− concentration for SCN attraction was 171–256 mM. RKN showed weak attraction to base and salt at low J2 concentration but increasing attraction at a greater nematode concentration. The pH and inorganic salts affect nematode behavior, accumulation, and survival. These findings provide new considerations for strategies to manage plant-parasitic nematodes under field conditions.

Eco-friendly management of plant parasitic nematodes

Background/Objective: Root-knot nematodes and cyst nematodes are two important plant-parasitic nematodes that cause severe plant diseases in various plant species around the world. They act as obligate and biotrophic parasite within the plant body. The objective of the study is to review for suitable management to keep the nematode population density below the threshold level. Methods: In spite of several nematode control practices such as crop rotation, use of biopesticides or nematicides, each has some limitations of their use but biotechnological applications including RNAi or miRNA represent a potential breakthrough in the application of functional genomics for plant nematode control. Here, a comparison is made between some old and modern nematode management practices but recent data shows that application of RNAi or miRNA has a better option of nematode control in some crop plants. Findings: Efficacy and biotechnological success can be maintained by holistic grasping of several soil biological and ecological factors. Therefore, modern approaches those reviewed herein due to their usefulness in minimizing plant nematode populations and increasing crop yield should be incorporated into management systems. The scientific community has entered into a new era that shows the tools to actually unravel the underlying molecular mechanisms, making this an opportunity for a review of our current knowledge and better understanding. Application: These modern eco-friendly practices may not quickly perform as synthetic chemicals, but they are pest specific, non-toxic to humans or environment, and also serves as a sustainable tool for disease management. Novelty: The present communication identifies plant nematode control approaches with emphasis on modern research. This review article emphasized the importance of modern biotechnological approaches for better crop yield than the common older practices. Keywords: Root-Knot nematode; biotrophic Parasite; threshold level; nematicides; biopesticide; micro RNA

Spatial and spatiotemporal analysis of Meloidogyne hapla and Pratylenchus penetrans populations in commercial potato fields in New York, USA

Summary Meloidogyne hapla and Pratylenchus penetrans are important plant-parasitic nematodes affecting potato in New York and the Northeastern United States, yet little is known of their spatial patterns and spatiotemporal dynamics. Spatial patterns of M. hapla and Pratylenchus spp. were quantified using semivariogram analysis and Spatial Analysis by Distance IndicEs (SADIE). Nematode populations were assessed within each of three commercial potato fields in 2016 and 2017, with fields sampled on two occasions in-season. Semivariogram analysis and ordinary kriging indicated initial population densities to be spatially dependent over an average range of 110 m for M. hapla and 147 m for Pratylenchus spp. SADIE indicated Pratylenchus spp. to be significantly aggregated in nearly all fields (10 of 12 samplings, to 2.113). Meloidogyne hapla populations were aggregated in only three of 12 samplings ( to 1.738). Spatiotemporal analysis using the association function of SADIE indicated a strong and significant association between initial and final population densities of M. hapla and Pratylenchus spp. within fields. This information is fundamental for the development of enhanced sampling protocols for estimation of plant-parasitic nematodes and evaluating the feasibility of site-specific nematicide application in New York potato fields.

Efficacy of a Soil Disinfection Machine for Fumigants to Clover Cyst Nematode

Clover cyst nematode, Heterodera trifolii, is one of the most important plant-parasitic nematode on Kimchicabbage in highland in Korea. Recently, a demand of soil disinfection machine for fumigants is increasing. This study was conducted to assess the control effects of a newly developed prototype soil disinfection machine to the cyst nematode. Two fumigants, dimethyl disulfide (DMDS) and metam sodium (MNa), were treated using the machine in a field, which was infected with the cyst nematode. After 4 weeks, control effects of fumigants were assessed as eggs hatching rates inside of cysts extracted from the soil, and as a number of females reproduced in roots of Kimchi-cabbage. DMDS (39 l/10 a) suppressed over 99.0% of the eggs hatching rate and the number of females reproduced. On the other hand, MNa (29 l/10 a) controlled the egg hatching rates from minimum 78.3% to maximum 99.4%, and the number of females from 34.7% to 49.3%. The control effects of two fumigants to clover cyst nematode by treated depth were no significant differences statistically. These results showed that DMDS treatment using the soil disinfection machine was expected to have the control effects for the clover cyst nematode.

Identification of quantitative trait loci underlying resistance and tolerance to the rice root-knot nematode, Meloidogyne graminicola, in Asian rice (Oryza sativa)

Meloidogyne graminicola is one of the most important plant-parasitic nematodes in rice. Breeding for natural resistance and tolerance is considered one of the most economical and sustainable approaches to control this damaging pathogen. Quantitative trait loci (QTL) mapping was carried out in a recombinant inbred line (RIL) population derived from a cross between the Asian rice genotypes IR78877-208-B-1-2 and Dinorado. IR78877-208-B-1-2 is an aerobic rice genotype that is resistant and tolerant to M. graminicola. Dinorado is a traditional upland rice genotype from the Philippines that is characterized by its aroma and prized for its cooking quality. The host response of 300 F4 lines derived from this cross was evaluated in both nematode infested and non-infested concrete beds in the dry seasons of 2013 and 2014. Five genotypes were found consistently resistant while 13 genotypes were consistently partially resistant to M. graminicola. QTL mapping for M. graminicola resistance/tolerance, yield-contributing traits, and yield revealed four main effect QTLs (qJ2RS2.1, qJ2GRT2.1, qJ2RS3.1, and qJ2GRT3.1) associated with reduced nematode reproduction on chromosomes 2 and 3 and two QTLs (qGR3.1 and qGR5.1) associated with reduced root galling on chromosomes 3 and 5. Twenty main effect QTLs associated with yield-contributing traits and yield were also found. Our study further identified co-locating QTLs associated with nematode resistance, yield-contributing traits, and yield on chromosomes 3 and 5. QTLs harboring candidate genes, such as OsBAK1, OsDST, OsIPT4, and DUF26, for higher grain yield and tolerance to abiotic and biotic stress, were identified. These QTLs and the RILs that are consistently resistant and tolerant to M. graminicola, and which are high-yielding in nematode-infested fields, can be utilized in breeding programs to improve the resistance and tolerance of Asian rice to this important pathogen.

Distribution of Root-Lesion and Stunt Nematodes, and Their Relationship with Soil Properties and Nematode Fauna in Sugarcane Fields in Okinawa, Japan

Sugarcane cultivation in Japan has not yet focused on suppressing plant-parasitic nematodes. For proper nematode management, it is essential to know the spatial distribution of economically important plant-parasitic nematodes and free-living nematodes that play important roles in terrestrial ecosystems. We aimed to reveal nematode fauna and soil properties in 85 sugarcane fields of three major sugarcane producing islands in Japan, and to examine their relationship by using the mixed-effect model and by visualizing the spatial distributions using the inverse distance weighting (IDW) approach. The nematode community structures were analyzed by non-metric multidimensional scaling (NMDS). Among plant-parasitic nematodes in sugarcane, the root-lesion nematodes (Pratylenchus sp.) and the stunt nematodes (Tylenchorhynchus sp.) were widely distributed in these islands, yet the abundance and the species varied geospatially. Soil pH was significantly correlated with the abundance of Pratylenchus and Tylenchorhynchus species. The abundance of Pratylenchus and Tylenchorhynchus species were significantly correlated with soil pH. The abundance of Pratylenchus was significantly correlated with the abundance of free-living nematodes, the number of free-living nematode species, and exchangeable cation K+, as were the abundance of Tylenchorhynchus to the clay content and that of non-Tylenchorhynchus. This study also revealed that the three islands had different nematode faunas, which were explained especially by soil pH, texture, and exchangeable basic cations.

Plant growth-promoting rhizobacteria: a novel management strategy for Meloidogyne incognita on turfgrass.

Meloidogyne spp., root-knot nematodes, are among the most economically important plant-parasitic nematodes in turfgrass in the United States. Only a few nematicides are available or efficacious for plant-parasitic nematodes in turfgrass in the United States, and recent work has demonstrated the potential for microbial control of root-knot nematodes in field crops. The objectives of this study were to evaluate the efficacy of 104 plant growth-promoting rhizobacteria (PGPR) strains isolated from grasses in Alabama against M. incognita in vitro, and their ability to manage plant-parasitic nematodes in the glasshouse and microplot settings. In vitro mortality ranged from 0.9% to 94.6% by all PGPR strains screened. Ten individual PGPR strains and one three-strain blend (a total of 13 PGPR strains) were advanced to glasshouse and microplot screening. In the glasshouse, six of the 11 PGPR treatments significantly reduced M. incognita population density, with a few strains also promoting some root growth. In the microplot, five of the 11 PGPR treatments significantly reduced M. incognita population density. Of these strains, 11 were identified as Bacillus spp., one as Stenotrophomonas rhizophila and one as Paenibacillus sonchi. Eight of these strains also were found to have nitrogenase activity, and seven had the ability to produce siderophores, showing a potential mechanism for growth promotion. Overall, results indicate that multiple strains of Bacillus spp. and one strain of S. rhizophila have the potential to reduce M. incognita population density and enhance turfgrass root growth. © 2020 Society of Chemical Industry.

First Report of Northern Root-Knot Nematode Meloidogyne hapla on Codonopsis pilosula in China

Worldwide, root-knot nematodes are among the most important plant-parasitic nematodes infecting and causing yield losses on many important plant species. They can cause extensive galling on plant roots, leading to serious economic losses (Azevedo de Oliveira et al. 2018). Codonopsis pilosula is used extensively in traditional Chinese herbal medicine and is a major economic crop in Gansu province. In the summer of 2019, a survey for plant-parasitic nematodes was conducted in Gansu province, northwest China. During the survey, 35 out of 76 fields of C. pilosula had plants exhibiting stunting, decline, and extensive galling on the secondary and tertiary roots. These are typical symptoms of infection by root-knot nematodes. Females, males, J2s, and eggs collected from roots of C. pilosula had the following morphometric characters: the perineal pattern of females (n = 10) were round-shaped, with low dorsal arches and small punctations near the anus, lateral line marked. Females (n = 20): body length (L) = 579.06 ± 50.19 μm (511.42 to 677.41 μm), maximum body width (W) = 423.81 ± 29.11 μm (396.72 to 467.41 μm), stylet length = 9.93 ± 0.88 μm (8.71 to 11.72 μm), distance from dorsal esophageal gland opening to the stylet knot (DGO) = 4.93 ± 0.42 μm (3.91 to 5.84 μm), stylet median bulb width (MBW) = 29.67 ± 3.61 μm (24.41 to 35.31 μm). Males (n = 10): L = 1,021.75 ± 106.38 μm (885.09 to 1,230.52 μm), stylet length = 17.15 ± 1.41 μm (15.27 to 19.89 μm), DGO = 5.04 ± 0.61 μm (4.24 to 5.83 μm), MBW = 9.82 ± 2.09 μm (7.11 to 14.24 μm), spicule length = 21.97 ± 1.67 μm (19.54 to 24.59 μm). J2s (n = 20): L = 363.66 ± 25.96 μm (322.41 to 398.88 μm), a = 24.41 ± 4.32 (21.33 to 27.12), stylet length = 10.41 ± 0.79 μm (9.01 to 11.32 μm), DGO = 4.01 ± 0.56 μm (3.22 to 5.13 μm), tail length = 53.15 ± 10.56 μm (32.74 to 71.24 μm). Eggs (n = 20): L = 73.92 ± 4.35 μm (68.43 to 80.13 μm), W = 25.19 ± 3.94 μm (20.48 to 30.74 μm). These morphological characteristics are consistent with Meloidogyne hapla Chitwood, 1949 as described by Whitehead (1968). Molecular analysis was conducted for further research; DNA was isolated from four individual females, and then the ITS region and D2/D3 region of 28S were amplified with primers18S/26S (Vrain et al.1992) and D2A/D3B (Al-Banna et al. 2004), respectively. The D2/D3 region of 28S sequence and ITS sequence were deposited in GenBank under accession numbers MN752204 and MN752202, respectively. D2/D3 region of 28S sequence was 99.84 to 99.91% identical to those of M. hapla from China (KJ755187), Myanmar (MN446015), and Japan (KF430798). The ITS region sequence was 99.31 to 99.61% identical to several sequences of M. hapla from GenBank, including ones from Spain (MH011978), Taiwan (KJ572385), the United States (AY268108), and Japan (LC030357). Furthermore, species identification was also confirmed using PCR to amplify with M. hapla-specific primers Mh-F/Mh-R (Feng et al. 2008). An expected PCR fragment of approximately 462 bp was obtained, which was consistent with M. hapla reported. No amplification products were observed in the control. A pathogenicity test of this M. hapla population was carried out in a growth chamber maintained at 20 to 25°C. Eight healthy C. pilosula seedlings were transplanted into plastic pots (one plant per pot). After 2 weeks, the roots of six plants were inoculated with 3,000 J2s and eggs per root system, and two uninoculated plants were used as a control. After 65 days, all inoculated plants exhibited yellowish leaves and stunting and had extensive galling on roots, which resembled those on field-grown plants. No galling or symptoms were observed on control plants. The final population density was quantified, and mean nematode reproduction factor (final population/initial population) was 4.3. These results confirm this root-knot nematode population on C. pilosula is M. hapla. To our knowledge, this is the first report of M. hapla in Gansu province and the first report of C. pilosula as a new host of M. hapla.

Screening for Resistance to Meloidogyne enterolobii in Capsicum annuum Landraces From Mexico.

Meloidogyne enterolobii has become an economically important plant parasitic nematode worldwide because of its high aggressiveness, increasing geographic distribution, wide host range, and pathogenicity in pepper (Capsicum annuum) cultivars carrying resistance genes to Meloidogyne incognita, Meloidogyne arenaria, and Meloidogyne javanica. The objectives of this study were to identify landraces of peppers resistant to M. enterolobii and analyze the relationship between resistance indicators and the phenotype parameters of plant height, stem width, leaf length, leaf width, relative chlorophyll, and number of flowers. Ninety landraces of C. annuum were collected from several states of Mexico and were inoculated with 2,000 eggs of M. enterolobii. Eleven resistant landraces were selected and confirmed with a second inoculation experiment. Seventy-five days after inoculation, in both experiments, the resistance of landraces UTC66, UTC90, UTC67, UTC88, and UTC81 to M. enterolobii was consistent. Although genotypes UTC24, UTC79, UTC65, UTC68, UTC69, and UTC25 were susceptible, these landraces had a significantly higher proportion of resistant plants, less root galling, and a lower reproductive index, in comparison with the rest of the 79 genotypes and the susceptible control, which were highly susceptible in both experiments. There was no correlation between resistant indicators and phenotypic parameters, although plant height, relative chlorophyll, and number of flowers were in general significantly affected compared with noninoculated controls, indicating that the nematodes reduce the growth and yield of peppers. Results indicate that all resistant plants from these landraces are promising sources of resistance for the development of pepper cultivars resistant to M. enterolobii.

Development of quantitative detection method for Meloidogyne incognita by qPCR

The root-knot nematode (Meloidogyne spp.) is the most important plant-parasitic nematode genus, they are the most common and destructive pathogens in this group. They produce some of the most drastic symptoms in plants and can significantly reduce the yield of crops. In order to achieve deploy an efficient method of plant-parasitic nematode management, is necessary an identification and quantification accurate and reliable of plant-parasitic nematodes. The aim of this study was to analyze samples in qPCR to detect and quantify M. incognita, in the field samples, comparing different methods of extraction of DNA and its efficacy in establishing the number of individuals. For this purpose the effectiveness of different DNA methods of extraction was compared through the values of CT intervals. For standard curve and method comparisons, we used nematodes multiplied in a greenhouse and carefully separated in the specific quantities of the experiments. For the number of individuals experiment field samples previously counted under an optical microscope were used. The DNA extraction was made from 100 nematodes by the methods: CTAB, Phenol: Chloroform and commercial kit (PureLink® Genomic DNA Kit, Invitrogen). In the comparative analysis using the three methods of DNA extracting from 100 nematodes, it was observed that commercial kit and CTAB methods obtained CT values similar. The CTAB method of extraction, showed less variation in the repeats and greater linearity of standard curve in comparison with other methods tested. So, it was possible to quantify the samples through the CT value intervals, established from different numbers of individuals (1, 10, 25, 100, 250, 500 and 750), in field samples. This study demonstrated that qPCR technique is an alternative sensitive and reliable for the quantification of M. incognita to support laboratories of diagnose and field survey.

Morphological and Molecular Characteristics of Pratylenchus coffeae from the Origin of Robusta Coffee Plantation in Malang, East Java

Pratylenchus coffeae is the most important plant-parasitic nematode in Robusta coffee plantations. Information regarding morphology, morphometric and molecular characters of P. coffeae has not been reported in Indonesia. This study is aimed to describe those characters of P. coffeae that attack Robusta coffee. Root samples were taken from Robusta coffee plantation in Malang, East Java. Nematode extractions was conducted using a mist chamber method. Morphology and morphometric characters were observed from the permanent nematode slides. Single nematode DNA extract was amplified at the D2D3 segment of 28S rRNA and ITS1-5.8S-ITS2 rRNA with universal primers. Amplicon was sequenced and analysed for phylogenetic tree relationships. Female morphological key character of P. coffeae observed are: lip with two annulations, four lateral lines, esophageal overlap with intestine ventrally, monodelphic, and truncated tail shape. Male spicules curved ventrally. Female morphometrics are: n=26, L = 556.4 μm, DGO = 2.4 μm, anterior gonad = 174.8 μm, a = 28.5, b = 6.1, b’ = 4.1, c = 20.1, c’ = 2.3, V = 81.7. A Male is smaller than a female with n=24, L = 505.9 μm, a = 32.3, b = 5.5, b '= 3.9, c = 15.3, c' = 2.8 and T = 40.6. The molecular characters of P. coffeae were investigated for two isolates, namely SA1 and SA2. Based on the D2D3 and ITS1-5.8S-ITS2 regions, isolate SA1 has similarity level of 99% and 97% to the P. coffeae from NCBI. Similar result was shown by Isolate SA2 with similarity of 100% and 100% respectively. Phylogenetic tree analysis using Maximum Likelihood at the D2D3 segment of 28S rRNA and ITS1-5.8S-ITS2 regions showed that P. coffeae in this study was included in one clade with P. coffeae from several countries.

Transcriptional signatures of invasiveness in Meloidogyne incognita populations from sub-Saharan Africa

Meloidogyne incognita is an economically important plant parasitic nematode. Here we demonstrate substantial variation in the invasiveness of four M. incognita populations relative to tomato. Infective (J2) stage transcriptomes reveal significant variation in the expression of protein-coding and non-coding RNAs between populations. We identify 33 gene expression markers that correlate with invasiveness, and which map to genes with predicted roles in host finding and invasion, including neuropeptides, ion channels, G Protein-Coupled Receptors, cell wall-degrading enzymes and microRNAs. These data demonstrate a surprising diversity in microRNA complements between populations, and identify gene expression markers for invasiveness of M. incognita, to our knowledge for the first time.

Effects of α-pinene on the pinewood nematode (Bursaphelenchus xylophilus) and its symbiotic bacteria

The pinewood nematode (PWN), Bursaphelenchus xylophilus, is an important plant-parasitic nematode that can cause severe mortality of pine trees. This PWN-induced harm to plants may be closely related to the abundance and diversity of the symbiotic microorganisms of the parasitic nematode. In this study, nematodes were divided into untreated and antibiotic-treated groups. Nematodes were treated by fumigation with different amounts of α-pinene, and the resultant mortality rates were analyzed statistically. Concentrations of symbiotic bacteria were calculated as colony-forming units per nematode. High-throughput sequencing was used to investigate the bacterial community structure. The results showed that the mortality of nematodes increased slightly with an increasing concentration of α-pinene, and nematodes untreated with antibiotics were more sensitive to α-pinene than those treated with antibiotics. The highest abundance of symbiotic bacteria was obtained via medium and low levels of α-pinene, but for which community diversity was the lowest (Shannon and Simpson indexes). The proportion of Pseudomonas spp. in the symbiotic bacteria of nematodes without antibiotics was relatively high (more than 70%), while that of Stenotrophomonas spp. was low (6%–20%). However, the proportion of Stenotrophomonas spp. was larger than that of Pseudomonas spp in the symbiotic bacteria associated with the antibiotic-treated nematodes. Pseudomonas sp. increased after pinene treatment, whereas Stenotrophomonas spp. decreased. These results indicate that although α-pinene has low toxicity to PWNs over a short time period, α-pinene ultimately influences the abundance and community diversity of the symbiotic bacteria of these nematodes; this influence may potentially disturb the development and reproduction of nematodes in the process of infecting pine trees.

Aptitud de cinco poblaciones de jitomate silvestre (Solanum lycopersicum var. cerasiforme) como hospedante del nematodo Nacobbus aberrans sensu lato

<em>Nacobbus aberrans</em> <em>sensu lato</em> es uno de los nematodos más importantes en el cultivo de jitomate. Para su manejo, es de importancia el estudio de estrategias sostenibles como la resistencia genética, comúnmente encontrada en parientes silvestres de los cultivos. Al respecto, surgió el interés por conocer la respuesta de poblaciones locales (Michoacán, México) de jitomate silvestre (<em>Solanum</em> <em>lycopersicum</em> var. <em>cerasiforme</em>) a la inoculación con juveniles de segundo estadio de <em>N. aberrans</em> <em>s.l.</em> Se montaron tres experimentos (E1, E2, y E3). Se evaluaron cinco genotipos silvestres y uno cultivado (cv. Río grande). A los 7 y 21 días posteriores a la inoculación (dpi) se evaluó el número de nematodos dentro de la raíz, y a los 45 y 60 dpi el agallamiento de raíces. En E1 y E2, a 7 y 21 dpi se encontraron los estadios J2 y J3-J4. En los tres experimentos ocurrió agallamiento, y a 60 dpi la producción de huevos fue evidente. <em>N. aberrans s.l.</em> invadió las raíces, y completó su desarrollo y reproducción. Estos resultados revelan la aptitud de las cinco poblaciones mexicanas de jitomate silvestre como hospedantes del nematodo, y sugieren la necesidad de explorar otras solanáceas silvestres como posibles fuentes de resistencia al nematodo.

In Vitro Acquisition of Specific Small Interfering RNAs Inhibits the Expression of Some Target Genes in the Plant Ectoparasite Xiphinema index.

Xiphinema index is an important plant parasitic nematode that induces direct damages and specifically transmits the Grapevine fanleaf virus, which is particularly harmful for grapevines. Genomic resources of this nematode species are still limited and no functional gene validation technology is available. RNA interference (RNAi) is a powerful technology to study gene function and here we describe the application of RNAi on several genes in X. index. Soaking the nematodes for 48 h in a suspension containing specific small interfering RNAs resulted in a partial inhibition of the accumulation of some targeted mRNA. However, low reproducible silencing efficiency was observed which could arise from X. index silencing pathway deficiencies. Indeed, essential accustomed proteins for these pathways were not found in the X. index proteome predicted from transcriptomic data. The most reproducible silencing effect was obtained when targeting the piccolo gene potentially involved in endo-exocytosis of synaptic molecules. This represents the first report of gene silencing in a nematode belonging to the Longidoridae family.

Evaluation of fluopyram for southern root-knot nematode management in tomato production in China

The southern root-knot nematode (Meloidogyne incognita) is one of major challenges tomato growers face in vegetable production; and phase out of methyl bromide and the restricted use of soil fumigants have been accelerating application of non-fumigant nematicides for control of this economically important plant-parasitic nematode. Fluopyram, a succinate dehydrogenase inhibitor fungicide, has been widely used to control fungal diseases in vegetable crops. However, in China, little information is currently available about the efficacy of fluopyram against M. incognita and its effect on tomato yield. In this study, the nematicidal effect of fluopyram on M. incognita was investigated under laboratory and field conditions in China. In the laboratory, fluopyram was highly toxic to the second-stage juveniles (J2) and the eggs of M. incognita with the median lethal concentration (LC50) value of 2.78 and 1.70 mg L−1, respectively. In the field trials, fluopyram was effective in reducing population levels of M. incognita, meanwhile enhancing plant growth, particularly at 480 and 640 g ha−1 in two consecutive years, which was significantly greater than that of abamectin (a standard treatment) at 480 g ha−1. Moreover, there was a yield increase of 21.4%-58.5% from the treatments with fluopyram at three doses compared with the untreated control. The results from this study indicated that fluopyram was effective against M. incognita and could be used for control of root-knot nematodes in tomato production, while enhancing tomato growth and yield.

Grass Root-Knot Nematode Meloidogyne graminis Whitehead, 1968 (Nematode: Tylenchida: Meloidogynidae)


 
 Root-knot nematodes (Meloidogyne spp.) are the most important plant-parasitic nematodes worldwide, with most temperate and tropical crops suffering yield losses from one or more species of Meloidogyne. Root-knot nematodes are the most widely recognized plant-parasitic nematodes because the characteristic galls or knots they cause on plant roots are easily observed symptoms for diagnosis. Meloidogyne graminis is damaging to many turf and forage grasses. Due to the prevalence of this nematode on grasses, and the prevalence of grasses compared to other crops in the state, it is likely the most widespread species of root-knot nematode in Florida. It is of increasing concern due to the rising importance of turfgrasses in the Florida economy, the susceptibility of grasses to this nematode, and implementation of new diagnostic techniques that have brought to light the damaging potential of this nematode.
 This document is also available on the Featured Creatures website at http://entomology.ifas.ufl.edu/creatures.
 https://edis.ifas.ufl.edu/in1231

Occurrence and seasonal variation of the root lesion nematode Pratylenchus neglectuson cereals in Bolu, Turkey

The root lesion nematode Pratylenchus spp. is one of the most important plant-parasitic nematodes causing global cereal yield losses. Effective management of plant-parasitic nematodes depends on reliable management strategies and comprehensive datasets estimating the distribution, abundance, and population change of nematode species. This study reports the occurrence of Pratylenchus neglectus in wheat-growing districts during the 2014/15 and 2015/16 cropping seasons in Bolu, Turkey. Pratylenchus neglectus was identified by both morphological and molecular methods. The nematode was detected in 11.6% of samples collected from five districts. On average, P. neglectus numbered 1556 nematodes/kg soil, while 12% of samples had more than 2500 nematodes/kg soil. P. neglectus population dynamics were evaluated by sowing a susceptible winter wheat variety (Bezostaya) in a naturally infested field near the Çaydurt district of Bolu during the 2014/15 and 2015/16 cropping seasons. There was a positive correlation (P < 0.01) between nematode abundance in roots and surrounding soil temperature. The highest abundance of nematodes in roots occurred during May (average temperature: 22 °C), while the lowest abundance was during December-March (average temperature: 5 °C). The initial population was measured as an average of 60 nematodes/100 g soil. The reproduction rate of P. neglectus ranged from 0.7 to 4.8 individuals.

Distribution and community structure of plant-parasitic nematodes and their relationship with some soil properties in betel vine-growing regions of West Bengal, India

Summary The distribution and community structure of plant-parasitic nematodes associated with betel (Piper betle) vine and their relationship with soil chemical properties were investigated in four major growing regions of West Bengal, India. Ordinary kriging method was applied to infer the patterns of spatial distribution of major plant-parasitic nematodes across the growing regions. Meloidogyne and Rotylenchulus were found to be the most abundant genera in betel vine crops in all growing regions. Co-inertia analysis between soil properties and nematode abundance indicated that soil chemical characters significantly affect abundances of plant-parasitic nematodes. The type of betel vine crop (sweet and bitter) also has a significant effect on the abundance of plant-parasitic nematodes, with the highest abundance of Meloidogyne reported from the bitter type of betel crop. Spatial distribution depicted a higher abundance of Meloidogyne throughout the North Bengal growing region. Root-knot and reniform nematodes are two important plant-parasitic nematodes of betel vine that might cause economic yield loss to the growers in West Bengal.