Brazil has one of the largest varieties of aquatic ecosystems and rich freshwater biodiversity, but these components have constantly been damaged by the expansion of unsustainable activities. Free-living nematodes are an abundant and ubiquitous component of continental benthic communities, occurring in all freshwater habitats, including extreme environments. Despite this, hardly any studies have examined the generic composition of nematodes in different latitudes and the geographic overlap of assemblages. We provide data on nematode genera from six regions in Brazil, over a north-south gradient spanning about 4000 km, encompassing rivers, coastal lakes, and reservoirs with different levels of human impact. Interpolation/extrapolation curves were generated and the zeta diversity was used to assess the overlap of nematode assemblages. Freshwater nematode assemblages comprised 54 families and 132 genera. Mononchidae, Monhysteridae, Chromadoridae, Tobrilidae and Dorylaimidae were the most diverse families. Differences in diversity and high turnover of genera were found among regions, probably related to stochastic processes. Mononchus was the only widely distributed genus. Our results revealed a high biodiversity of free-living freshwater nematodes among the regions. The limited spatial coverage of the data reveals an enormous knowledge gap in a country with 12% of the world’s freshwater resources. The lack of spatial patterns, e.g., latitudinal variation, suggests that freshwater nematode assemblages are primarily structured by the intrinsic properties of habitats. This reinforces the uniqueness of freshwater ecosystems and suggests that the nematode assemblages may be sensitive to environmental disturbances, since the limited distributions of taxa may lead to lower resilience.
Meloidogyne graminicola is a major plant pathogen damaging rice. Altering a plant susceptibility gene that critically facilitates compatibility is considered one of the most effective strategies to control plant pathogens. However, no resource is currently available regarding M. graminicola susceptibility genes in Indica rice cultivars. In this study, transcriptome analysis was used to elucidate nematode-responsive genes to the two susceptible Indica rice cultivars ‘Guinongzhan’ and ‘Wushansimiao (R534)’ with distinct levels of susceptibility to M. graminicola at 3 days post-inoculation (dpi). A total of 33157 transcripts corresponded to the predicted genes in the Indica rice genome. Among these, 2062 and 1386 differentially expressed genes (DEGs) were identified in ‘Guinongzhan’ and ‘Wushansimiao (R534)’, respectively, as a result of nematode infection. Cluster analysis showed that 2184 DEGs were commonly regulated and 503 DEGs were differentially regulated in ‘Guinongzhan’ and ‘Wushansimiao (R534)’. These DEGs were involved in defence responses, the Ca2+ signal pathway, cell wall, hormone pathways, the ubiquitin proteasome system and transcription factors. In addition, candidate genes that may be involved in rice defence responses and susceptibility to M. graminicola were identified, and some of them were further validated by quantitative real-time RT-PCR. The transcription data reveal insights into the susceptible rice gene expression pattern changes upon nematode infection, and provide a novel set of candidate defence-related and susceptibility genes in Indica rice cultivars for M. graminicola.
The acquired resistance of plants to root-knot nematodes (Meloidogyne spp.) can be achieved by applying chemical inducers, such as β-aminobutyric acid (BABA). Recently, the use of metal nanoparticles with multifunctional use against plant-parasitic nematodes has been presented. In this study, silver nanoparticles (AgNPs) were synthesised using the aqueous leaf extract of Malva sylvestris. The effect of different AgNPs concentrations on hatching and mortality of the second-stage juveniles (J2) of Meloidogyne javanica was investigated in vitro. The effects of AgNPs on eggplants infected with 0, 1, 2, 4 and 8 eggs (cm3 soil)−1 were investigated under glasshouse conditions. The combined effects of AgNPs and BABA on eggplants infected with 4 and 8 eggs (cm3 soil)−1 were investigated in another study. The results showed that increasing the concentration of AgNPs the hatching of M. javanica decreased and the mortality of J2 increased. The number of eggs, galls, egg masses and reproduction factor in plants treated with AgNPs infected with 4 eggs (cm3 soil)−1 decreased by 43.4, 24.7, 23.5 and 43.2%, and in plants infected with 8 eggs (cm3 soil)−1, decreased by 64.5, 25.5, 63.1 and 64.5%, respectively, compared to control plants. The reproduction factor in infected plants with 4 and 8 eggs (cm3 soil)−1 that were treated with BABA (1 mM) and AgNPs decreased by 51.6 and 55.9%, respectively, compared to control plants. The results of this study demonstrated the effects of BABA, AgNPs and the combination of these two substances in reducing the damage of different inoculum densities of M. javanica in eggplant.
Aphelenchoides roulingae n. sp. is described and illustrated. This new species was isolated from Xylocopa collaris sauteri collected at Fushan, Yilan county, Taiwan. Typologically, the new species is characterised by a three-lined lateral field, conical female tail with various and not pointed termini, male spicule with well-developed and slightly dorsally truncate condylus, blunt triangular-shaped rostrum and unevenly ventrally curved dorsal contour of the spicule blade (calomus-lamina complex). The combination of typological characters of the new species is unique. Aphelenchoides roulingae n. sp. shares the three-lined lateral field and female tail shape with ‘A. helicus’, which was previously transferred to Robustodorus from Aphelenchoides, but can be differentiated from that species by its longer and more slender female tail, narrower female tail tip, and longer female stylet. In addition, the spicule morphology of A. roulingae n. sp. is unique and not similar to that of any other Aphelenchoides species. Phylogenetically, the new species forms a well-supported clade with the other Xylocopa bee-associated species, A. xylocopae, but can be typologically and molecularly distinguished from the species. In addition to the taxonomic description, some typological characters of the genus Aphelenchoides are discussed.
This paper describes a new species of Bastiania, presents a new record and redescribes a known species of Tripyla. These nematodes are all in the order Triplonchida and were collected from Shanxi Province, North China. Bastiania sinensis sp. n. is characterised by having the female with a relatively slender body 1049-1295 μm long, dorsally arcuate after heat relaxation, with outer labial setae and cephalic setae in a single circle, an oval amphid, 7-8 laterodorsal cervical setae scattered in the pharyngeal region, orthometamenes and pseudocoelomocytes present, tail conoid with a mucron 1-2 μm long, two pairs of caudal setae present, a = 58.1-75.5, b = 4.0-4.6, c = 12.7-19.7, c′ = 4.1-7.8 and V = 61.1-67.7. Males were not found. Tripyla aquatica is recorded for the first time from China, and is redescribed. Tripyla setifera has been reported from China but without a detailed description – now provided. In addition, phylogenetic relationships among the species were analysed using data from the near full length small subunit (SSU) and D2-D3 segments of large subunit (LSU) of rRNA genes. Bastiania sinensis sp. n. is monophyletic with the Bastiania sequences available in GenBank, but is on an independent branch supporting its status as a separate species; T. aquatica and T. setifera are monophyletically clustered with known Tripyla species and grouped together with sequences from their respective species.
Bursaphelenchus paraleoni n. sp. was isolated from Loblolly pine, Pinus taeda, logs from the USA. The new species is characterised by a lateral field with three lines, 13-16 μm long stylet with small basal swellings, and the excretory pore located slightly posterior to the nerve ring. The male spicules are mitten-shaped, the lamina smoothly tapering towards the distal tip. The condylus is broadly rounded, with a small dorsally bent hook, rostrum triangular or conical with finely rounded tip, and cucullus absent. One midventral precloacal papilla, one adcloacal pair and two postcloacal pairs of genital papillae are present. The bursal flap is long and spade-like with the posterior margin truncate or irregular. Females have a small vulval flap 4-6 μm long, a post-vulval uterine sac extending for 34-49% of the vulva to anus distance, a very long tail with slight ventral curvature, mostly filiform and with a finely rounded terminus, occasionally bluntly rounded. Huge variation in the tails of males and females were observed in a culture. It is similar to species of B. eidmanni, B. leoni, and B. silvestris in the leoni-group but detailed phylogenetic analysis based on 18S, ITS and D2-D3 28S sequences confirmed it as a new species.
The root-knot nematode, Meloidogyne javanica, is the most damaging species of plant-parasitic nematodes in eggplant cultivation in Iran. We studied the effect of pistachio and date palm biochars, vermicompost and a mixture of each of these biochars with vermicompost on M. javanica. To investigate the effect of these organic materials on survival, hatching and attraction of the second-stage juvenile (J2) towards the root, bioassays were performed in the laboratory using extracts of organic material. Vermicompost extract increased J2 mortality and decreased hatching and the number of J2 attracted to the eggplant roots. However, either type of biochar alone or mixed with vermicompost did not cause J2 mortality, nor did they inhibit hatching and attraction of J2 towards the root. To determine the effect of organic matter on J2 invasion and reproduction, pot experiments were performed in a completely randomised design with four replications in the glasshouse. Vermicompost reduced the number of J2 that penetrated the roots, number of egg masses and the final population of M. javanica eggs and J2. The suppressing effect of vermicompost might be attributed to the release of toxic compounds such as ammonium and improved soil nutrient and plant growth, leading to plants more tolerant to nematode damage. Pistachio and date biochars alone or combined with vermicompost had no adverse effect on the nematode reproduction compared to non-treated soil. Both types of biochar reduced the suppressing effect of vermicompost, most probably due to the absorbance of suppressive compounds in vermicompost by the high surface area of the biochar.
Despite considerable knowledge of distribution, biology and parasitic variability (PV) of Meloidogyne hapla in cropping systems, how its PV relates to soil health conditions remains unknown. This study investigated the relationship between the presence or absence of M. hapla with soil food web and the abundance of nematode community in muck (high organic matter) and mineral soils of 15 agricultural fields and adjacent natural vegetation across three vegetable production regions of Michigan, USA. Meloidogyne hapla was present in all regions and all muck soils, but only in some mineral soils. It was present in soils with degraded and disturbed soil food web conditions, but there was no pattern with nematode trophic group abundance. However, principal component analysis showed distinct relationships among M. hapla presence or absence, soils, nematode abundance parameters in agricultural and natural vegetation. The study lays down a foundation for more targeted investigations to understand any links between the PV of M. hapla and its soil environment.