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In: Nematology

Summary

Bursaphelenchus taedae sp. n. of the eggersi-group was detected in loblolly pine logs from the USA together with B. antoniae. It is characterised by a relatively small stylet with basal swellings, a lateral field with three lines, and the excretory pore located at the level of the nerve ring. The female has a very small extension of the anterior vulval lip over the vulva (= a ‘vulval flap’), a long PUS extending for 40.1-67.8% of vulva to anus distance, and hook-like tail conical, gradually tapering to a finely rounded or broadly rounded terminus. The male spicules are 17-22 μm long in chord, only slightly ventrally curved, condylus short, truncate, slightly dorsally bent to dorsally hooked, rostrum ca 3-4 μm long, close to the proximal spicule end, without cucullus. Seven genital papillae present. Bursaphelenchus taedae sp. n. can be distinguished from other species of the eggersi-group by morphological and molecular characters.

In: Nematology

Summary

The entomopathogenic nematode (EPN), Heterorhabditis bacteriophora, is an important biological control agent worldwide. Industrially produced EPN need to meet the climatic requirements for the control of pests in field agriculture in autumn and spring when temperatures are low. For this trait (virulence at low temperature), previous EPN improvement attempts relied on phenotypic selection and the selected trait had low stability. The use of molecular markers can increase the efficacy of EPN breeding by tracking traits associated with specific genotypes. To date, fewer than 200 polymorphic and reproducible sequence-tagged molecular markers in H. bacteriophora have been reported. Here, we enhanced the palette of highly polymorphic genetic markers for this EPN by applying genotyping by sequencing (GBS). By analysing 48 H. bacteriophora homozygous wild-type inbred lines from different origins, we determined 4894 single nucleotide polymorphisms (SNPs) with at least one polymorphism along the tested set. For validation, we designed robust PCR assays for seven SNPs, finding 95% correspondence with the expected genotypes along 294 analysed alleles. We phenotyped all lines for their virulence at low temperature (15°C) against mealworm and observed infectivity ranging from 38 to 80%. Further, we carried out association analyses between genotypic and phenotypic data and determined two SNPs yielding potential association with H. bacteriophora virulence at low temperature. The use of these candidate SNPs as breeding markers will speed up the generation of strains better adapted to low temperature in this species. The generated set of lines and SNP data are a versatile tool applicable for further traits in this EPN.

In: Nematology

Summary

Effectors synthesised in the pharyngeal glands are important in the successful invasion of root-knot nematodes. Meloidogyne javanica is among the nematodes that cause the most damage to various crops. In this study, an effector named MJ-10A08 of M. javanica was identified and investigated. Mj-10A08 was exclusively expressed in the dorsal pharyngeal gland cell and highly expressed in the parasitic second-juvenile stage of M. javanica. Transgenic tobaccos that over-expressed Mj-10A08 were more susceptible to M. javanica; however, host delivered RNAi of Mj-10A08 in tobacco significantly decreased the expression level of Mj-10A08 and the infection efficiency of M. javanica. Transient expression in tobacco leaves demonstrated that MJ-10A08 suppressed programmed cell death caused by BAX and Gpa2/RBP-1. Our results indicated that MJ-10A08 is implicated in the suppression of plant defence response during nematode infection and plays an important role in the parasitism of M. javanica.

Open Access
In: Nematology

Summary

Tylenchulus semipenetrans nematodes affect citrus crops and may develop resistance to commercially available nematicides. In this sense, two series of 1,3,4-oxa- and thiadiazole compounds have been recently synthesised and tested as nematicides against T. semipenetrans, demonstrating promising results. We report herein a molecular modelling study that combines these two series of congeneric compounds to form a single and enhanced data set. The chemical structures of these compounds were correlated with the respective nematicidal activities (pLC50) using multivariate image analysis (MIA) descriptors in quantitative structure-activity relationship (QSAR) analysis. The partial least squares (PLS) regression yielded reliable and predictive models (r20.85, q20.70, and rpred20.71). Therefore, novel 1,3,4-oxa- and thiadiazole derivatives were proposed and a few of them exhibited predicted nematicidal performance better than those of the parent compounds.

In: Nematology

Summary

Over the last few years, novel synthetic nematicides, such as Salibro™ nematicide (a.s. fluazaindolizine - Reklemel™ active), Velum Prime® (a.s. fluopyram) or Nimitz® (a.s. fluensulfone), have been commercialised in various regions around the world. Whilst considerable scientific information exists on their field efficacy against plant-parasitic nematodes, very little has been published on their bio-compatibility with beneficial soil fungi. In this paper in vitro studies are presented with various nematophagous (Athrobotrys, Monacrosporium, Harposporium, Purpureocillium), entomoparasitic (Beauveria, Isaria) and disease-suppressive (Trichoderma) fungi that were exposed to these nematicides under laboratory conditions. Assessments were made on their impact on radial growth and sporulation of those fungi. Clear differences in sensitivity to the nematicides were seen between the different fungi. Intrinsically, fluopyram showed the strongest adverse effects on the tested fungi that often became already visible at a concentration of 5 ppm (a.s.). Negative effects were significant at higher concentrations of 50 ppm. Fluensulfone showed limited adverse impacts on the tested fungi at 5 ppm (a.s.) but clearly inhibited most of the fungi at 50 ppm (a.s.). Fluazaindolizine had the least impact of the novel nematicides, with no adverse effects recorded on any species at 5 ppm (a.s.), and very minor growth reductions at 50 ppm (a.s.). Even when tested at 250 ppm (a.s.) fluazaindolizine still showed no impact on Purpureocillium lilacinum, as well as only a weak impact on some Trichoderma species. Vydate (a.s. oxamyl), which was often included as a traditional carbamate nematicide in the test, also showed excellent bio-compatibility with the tested fungi at concentrations of from 5 to 50 ppm (a.s.). Overall, the studies showed that beneficial soil fungi differ in their intrinsic sensitivity to these modern nematicides. These interactions may be considered when designing integrated nematode management programmes that leverage endemic or introduced biocontrol agents. However, it should be noted that additional studies under field conditions with recommended label rates of the products are needed to confirm the trends seen in these laboratory data.

In: Nematology

Summary

The Humuli group of the genus Heterodera contains species that parasitise dicotyledons and are characterised by a lemon-shaped cyst having a bifenestrate vulval cone (ambifenestrate for H. fici), long vulval slit and weak underbridge. Presently, the Humuli group includes seven species: H. amaranthusiae, H. fici, H. humuli, H. litoralis, H. ripae, H. turcomanica and H. vallicola. In this study we provided comprehensive phylogenetic analyses of COI and ITS rRNA gene sequences of species from the Humuli group using Bayesian inference, maximum likelihood, and maximum and statistical parsimony. All seven valid species from the Humuli group, one putatively new species belonging to this group and the willow cyst nematode, H. salixophila, sharing a common ancestor with the Humuli group, were analysed. Some 84 COI and 5 ITS rRNA new gene sequences from 37 nematode populations collected from 12 countries were obtained in this study. Our results confirmed that the COI gene is a powerful DNA barcoding marker for identification of populations and species from the Humuli group. Based on the results of phylogeographical analysis and age estimation of clades with a molecular clock approach, it was hypothesised that some species of the Humuli group primarily originated and diversified in Western and Middle Asian regions during the Pleistocene and Holocene periods and then dispersed from this region across the world. Two secondary diversification centres of the Humuli group were likely located in East and Southeast Asia, Russian Far East, and Oceania.

In: Nematology

Summary

A new species of the genus Ficophagus was recovered from the syconia of Ficus variegata from Shenzhen, Guangdong province, China. It is described herein as Ficophagus giblindavisi n. sp. and is characterised by possessing the longest stylet in males (35.1-45.8 μm) and most lateral incisures (5) of all currently described species in the genus, a short PUS (8.4-11.4 μm or 0.3 VBD long), excretory pore situated at or posterior to the nerve ring, amoeboid sperm, three pairs of subventral papillae on the male tail, rounded male tail tip with a mucron, absence of gubernaculum and sickle-shaped spicules with a terminal cucullus. Ficophagus giblindavisi n. sp. was differentiated from other sequenced species by the partial small subunit (SSU) rRNA gene and D2-D3 expansion segments of the large subunit (LSU) rRNA gene. Phylogenetic analysis with the LSU D2-D3 expansion segment sequence suggested that F. giblindavisi n. sp. is clustered in the same highly supported monophyletic clade with F. auriculatae and F. fleckeri.

In: Nematology

Summary

Ruehmaphelenchus americanum n. sp., isolated from southern yellow pine (Pinus taedae L.) from the USA is described and figured. It is characterised by a relatively stout body (a = 30 for females and males), three lines in the lateral field, both oocytes and spermatocytes arranged in two rows, male spicules relatively small (14-18 μm) with weakly developed condylus and rostrum, short tail with a bluntly pointed tip, seven papilliform genital papillae present, female vulva positioned at ca 82% of body length, vulval lips slightly protruding, post-uterine branch extending two-thirds of vulva to anus distance, tail cylindrical, ca two anal body diam. long, terminus forming a spike-like projection or mucron, 7.6-12.2 μm long, with pointed tip. The new species can be separated from 11 known species (except R. thailandae) by male genital papillae arrangement (the second and third pair adjacent vs separated). Detailed phylogenetic analysis based on 18S and 28S D2-D3 region ribosomal RNA (rRNA) sequences has confirmed the status of this nematode as a new species.

In: Nematology