The type population of Meloidogyne polycephannulata is synonymised with M. incognita based on morphological and morphometric characters, as well as biochemical, molecular and phylogenetic studies. Morphological variability and a wide host range were reported for M. incognita during its first description and later re-description. Meloidogyne polycephannulata was described in Brazil from specimens collected in a carrot field (type population). The esterase phenotype (Est) characterised for this species was identical to the phenotype Est I2 of M. incognita, the most ubiquitous phenotype used for diagnostics. Morphological and morphometric characters of the descriptions of the two nominal species showed major similarities, as well as variability within the range of variation detected in M. incognita. In PCR assays, three SCAR markers species-specific for M. incognita (incK14 F/R, Mi/FR and incB06 F/R) amplified the same fragments of 399 bp, 955 bp and 1200 bp, respectively, for populations in both species. In phylogenetic studies based either on concatenated sequences of ITS1-5.8S-ITS2, D2-D3 rRNA, mitochondrial COII regions or on RAPD and AFLP data, the populations of both species grouped in the same clade with high bootstrap support. Altogether, these results provide congruent evidence that the M. polycephannulata type isolate deposited at the Embrapa Cryopreserved National Collection of Root-knot Nematodes is not a valid species but rather a junior synonym of M. incognita.
Bacterial symbioses play important roles in shaping diverse biological processes in nematodes, and serve as targets in nematode biocontrol strategies. Focusing on the Xiphinema americanum species complex, we expanded upon recent research investigating patterns of coevolution between Xiphinema spp. and Xiphinematobacter spp., utilising two symbiont genetic markers of varying evolutionary rates. Phylogenetic analysis of nematode mitochondrial DNA (mtDNA) revealed five strongly supported major clades. Analysis of slow-evolving 16S rDNA in bacterial symbionts resulted in a phylogenetic topology composed of four major clades that grouped taxa highly congruent with the nematode mtDNA topology. A faster evolving protein-coding symbiont gene (nad) provided more phylogenetic resolution with seven well-supported clades, also congruent with the nematode mtDNA tree topology. Our results reinforce recent studies suggesting extensive coevolution between Xiphinema spp. and their vertically transmitted endosymbionts Xiphinematobacter spp. and illustrate the advantages of including genetic markers of varying evolutionary rates in coevolutionary and phylogenetic studies.
Natural volatiles released by the fungus, Annulohypoxylon sp. FPYF3050, were evaluated against the pine wood nematode (PWN), Bursaphelenchus xylophilus. Our results showed that volatile organic compounds (VOCs) caused 64.1 and 58.4% mortality of second-stage juveniles (J2) and mixed-stages (eggs, J2, third- and fourth-stage juveniles, and adults) of populations of PWN, but no inhibitive effects were detected on nematode eggs in the experiment. Analysis of the gases within the Petri plate by gas chromatography-mass spectrometry (GC-MS) showed a yield of an unique volatile with dominant 1,8-cineole in 77.4% relative area (RA) after 72 h treatment of nematodes with Annulohypoxylon sp. FPYF3050 and Botrytis cinerea. The commercial 1,8-cineole at concentrations of 2, 5, 10 and 15 μl ml−1 was applied to examine nematicidal activity. The results showed that 1,8-cineole had a 40-100% inhibition on the nematode eggs during 48 h treatment, more than 82.9% mortality of J2 after 24 h, 48 h and 96 h, and 18.7-91.9% mortality of the mixed-stage population, depending on the period after exposure. This result indicates that 1,8-cineole in the volatile gas emissions of Annulohypoxylon sp. FPYF3050 may play a crucial inhibitory effect on the pine wood nematode The nematicidal volatile gas from fungi may provide a useful biocontrol agent for controlling B. xylophilus.
Aphelenchoides medicagus n. sp. isolated in Ningbo Port, P.R. China, from dried leaves and shoots of Medicago sativa imported from the USA, is described. It is characterised by a lateral field with four lines (three bands), stylet 9.0-12.0 μm long, excretory pore situated at same level as, or slightly posterior, to the nerve ring, vagina sclerotised, female vulval flap absent, post-uterine sac short, spicules 9.2-14.2 μm long (median curved line), rosethorn-shaped, apex and rostrum rounded, poorly developed, female and male tail conical with terminus bearing star-like processes. The new species belongs to the Group 3 category of Aphelenchoides species sensu Shahina. Phylogenetic analyses based on 18S, ITS and 28S D2-D3 of rDNA and mtCOI sequences confirmed its status as a new species and closely related to A. besseyi and A. fujianensis.
One of the concerns for nematological research is the absence of information on standard nematode population densities to be used when screening to assess resistance/susceptibility levels of a genotype. In addition, the length of the growth period, especially for perennial crops such as coffee, must also be known. The objective of this work was to evaluate the ideal evaluation periods and population densities of the root-knot nematode, Meloidogyne incognita, for phenotyping Coffea arabica genotypes. Seedlings of coffee ‘Mundo Novo’ with five leaf pairs cropped in 700 cm3 plastic pots were inoculated with population densities of 700, 1400, 2800, 5600 and 11 200 eggs of M. incognita per plant and evaluated at 90, 120, 150 and 180 days after inoculation (DAI) to determine the nematode reproduction factor (RF). The use of population densities of M. incognita from 700-2000 nematodes with evaluations between 90 and 180 DAI was the most suitable to obtain higher RF values and allows earlier and more accurate evaluations, which reduces the time for phenotyping in genetic screening programmes.
Extracts of nine agricultural wastes prepared with five different solvents were assessed for their potential nematicidal activity against three nematode species, Aphelenchus avenae, Meloidogyne incognita and Pratylenchus neglectus, in in vitro condition. The 50% v/v hydro-ethanolic extracts showed the highest performance for two tested plant wastes of cabbage leaves and faba bean pods. These two extracts were tested on nematodes in three different concentrations. The highest in vitro nematistatic activity was recorded for 3000 and 1500 ppm of cabbage leaf extracts by 100% paralysis of all three nematode species after 48 h, and the highest nematicidal activity was recorded for the above-mentioned extract by 25-100% mortality depending on nematode species and extract concentration. A 14-94% mortality was recorded for all three species of nematodes after treatment with faba bean pod hydro-ethanolic extract in in vitro conditions. Hatching inhibition and repellent activity of cabbage leaf and faba bean pod extracts were observed in P. neglectus and M. incognita. In vivo assays confirmed the in vitro results when both of the extracts showed moderate to high inhibition of nematode population development and nematode infection parameters on tomato root system in pot experiments.
Salibro™ is a novel sulfonamide nematicide containing the active substance (a.s.) fluazaindolizine (Reklemel™ active). Its biochemical mode of action is presently unknown but in internal laboratory studies it exerted adverse effects on various fitness parameters (motility, mobility and infectivity) of two species of root-knot nematodes (Meloidogyne incognita and M. hapla). While not causing an immediate knock-down effect on second-stage juveniles (J2) during the first 24-48 h of exposure to concentrations of 1-50 ppm (a.s.), exposed J2 showed clearly visible symptoms of toxicological effects (including characteristic body postures) and started to lose both their mobility as well as infectivity. This decrease in mobility and infectivity was nonreversible, even if the J2 were washed, and was already observed after pre-exposure periods of 24-48 h at 1-50 ppm (a.s.). Lower temperatures during the exposure period (4-10°C) did not prevent toxicological effects of treated J2 but slightly delayed the time-to-effect. By contrast, various vermiform life-stages of the bacteriophagous nematode, Acrobeles buetschlii, did not show any signs of intoxication or reduced motility during continuous exposure to Salibro™ at up to 250 ppm (a.s.). Salibro™ slightly increased hatching of M. hapla but did not significantly impact the hatching of M. incognita at concentrations up to 50 ppm (a.s.). No adverse effects on hatching were observed for A. buetschlii at concentrations up to 250 ppm (a.s.). The results indicate that Salibro™ is an effective and selective nematicide and will be a useful new tool in sustainable nematode management.