Summary
Steinernema bakwenae n. sp. isolate SF857 has been isolated from a soil sample from the North West province of South Africa. The infective juveniles were isolated using Cobb’s decanting and ...sieving method, hand-picked from the nematode population and inoculated directly onto wax moth larvae. Morphological and molecular characterisation provides evidence for placing the new species in the Khoisanae-clade, adding a fifth member to this all-African clade. The new species is characterised by the following morphological features: third-stage infective juveniles with a body length of 1106 (1013-1233) μm, a distance from the anterior end to the excretory pore of 90 (81-103) μm, and a tail length of 87 (76-103) μm. The first-generation males can be recognised by a spicule length of 80 (66-89) μm and by a gubernaculum length of 51 (44-56) μm. The new species was confirmed by means of crossbreeding and characterised by means of sequences of the internal transcribed spacer (ITS), the partial 28S regions (D2-D3) of the ribosomal DNA and the mitochondrial cytochrome oxidase subunit (COI). Phylogenetic analyses show that S. innovationi and S. tophus are the closest relatives to S. bakwenae n. sp. in the Khoisanae-clade.
Summary
Globodera presently contains 13 valid and three as yet undescribed species. Three species, G. rostochiensis, G. pallida and G. ellingtonae, the potato cyst nematodes (PCN), cause significant ...economic losses on potatoes around the world. In our study we provide comprehensive phylogenetic analyses of 455 ITS rRNA, 219 COI and 164 cytb gene sequences of 11 valid and two undescribed species of Globodera using Bayesian inference, maximum likelihood and statistical parsimony. New 205 COI, 116 cytb and 21 ITS rRNA gene sequences were obtained from 148 populations of these species collected from 23 countries. The phylogenetic analysis revealed that Globodera displayed two main clades in the trees: i) Globodera from South and North America parasitising plants from Solanaceae; and ii) Globodera from Africa, Europe, Asia and New Zealand parasitising plants from Asteraceae and other families. Based on the results of phylogeographical analysis and age estimation of clades with a molecular clock approach, it is hypothesised that Globodera species originated and diversified from several centres of speciation located in mountain regions and then dispersed across the world from these regions during the Pleistocene. High genetic diversity of Bolivian populations of G. rostochiensis was observed for both mtDNA genes. Analysis of phylogenetic relationships of G. pallida and G. rostochiensis populations revealed incongruence in topology between networks inferred from mtDNA genes, which might be an indication of possible recombination and selective introgression events through gene flow between previously isolated populations. This puts some limitations on the use of the mtDNA marker as universal DNA barcoding identifier for PCN. Globodera bravoae syn. n. is proposed as a junior synonym of G. mexicana.
Entomopathogenic nematodes (EPNs) are microscopic roundworms that are found in soil worldwide. They deliver an important ecosystem service through preventing natural flares in insect reproduction by ...means of utilising the soil stages of insects as a food source and by acting as natural biocontrol agents. A survey of EPNs was conducted in the JS Marais Nature Reserve, Stellenbosch, in the Western Cape province of South Africa. Soil samples were baited with the larvae of three susceptible hosts, codling moth (Cydia pomonella), wax moth (Galleria mellonella) and mealworm (Tenebrio molitor) to determine the presence of EPN. Of the 76 soil samples collected across the reserve, 39 were found to be positive for the presence of EPN (51.32%). Among the positive samples, 87% contained Steinernema isolates, 8% contained Heterorhabditis and 5% contained the Oscheius sp. Morphological and molecular studies were performed to characterise the isolates to species level. The Steinernema species were identified as Steinernema khoisanae in 34 samples, and as Steinernema nguyeni in five samples. The only species of Heterorhabditis found was H. safricana, which was identified from three samples. An unknown Oscheius sp. was found in two samples. The reserve's population of S. khoisanae showed interesting inter-individual variation (93%) early in the internal transcribe spacer (ITS) region, leading to short single-usable sequences, which, in most cases, included only the ITS1 or ITS2 region. However, using the D2D3 confirmed their identity as S. khoisanae, with such occurring in all areas and soil types of the reserve. Conservation implications The undisturbed alluvial fynbos and renosterveld of the JS Marais Nature Reserve showed high EPN abundance and diversity in stark contrast to the agro-ecosystems present in the Cape floristic region. This finding, on a micro level, should be conserved for future bioprospecting in the fynbos for EPNs with potential as biocontrol agents.
Plant-parasitic nematodes of the genus
Cobb, 1913 comprise a complex group of nematode species, some of which are important vectors of plant viruses. During a field survey to determine the soil ...health of an abandoned honeybush (
) monoculture, a high density of the dagger nematode,
Lamberti & Bleve-Zacheo, 1979 (Nematoda, Dorylaimidae), was observed in soil around the roots of honeybush plants in an abandoned farmland at Bereaville, an old mission station in the Western Cape province of South Africa. Soil samples were taken from the rhizosphere of plants and nematodes were extracted from the soil using a modified extraction tray method. Specimen of the dagger nematodes were processed for scanning electron microscopy, morphological and molecular analysis. Molecular profiling of the nematode species was done in order to give an accurate diagnosis and to effectively discriminate the nematode from other species within the
group. Phylogenetic analysis based on the D2D3 expansion segment of the 28S gene supported a close relationship of species within the
group, however, the protein-coding cytochrome oxidase (
) of the mitochondrial gene provided a useful tool for distinguishing the nematode from other species within the group. This study represents the first report of
from South Africa.
Aphelenchoides arachidis is reported for the first time from South Africa and for the fourth time outside Nigeria. The A. arachidis -infested pods from South Africa showed the following symptoms: ...small seeds with the testa wrinkled and darker in colour than that of non-infested seeds; the pods showed dark lesions and some seeds within the pods showed early germination. Differences between the two South African and the Nigerian populations of A. arachidis include more lateral lines in some specimens (2-4 vs 2) and, on average, longer post-uterine sac length (extending for 74 (41-96) and 62 (33-82) vs about 50% of vulva to anus distance). Scanning electron micrographs of this species are presented for the first time. The ITS regions of ribosomal DNA were amplified, sequenced, aligned and compared with other sequences of Aphelenchoides species. Two pathogenic fungi, Thielaviopsis basicola and Neocosmospora vasinfecta , were also isolated from this material.
A highly fecund root‐lesion nematode parasitizing a variety of crops was discovered and found to be widespread in Kenya and South Africa. These populations were molecularly identical to Pratylenchus ...teres teres and P. teres vandenbergae based on D2‐D3 of 28S rDNA and Hsp90 sequences. However, based on morphological differences with the original description of P. teres and its different geographical distribution, Pratylenchus vandenbergae stat. nov., previously known as subspecies P. teres vandenbergae, is recognized as a separate species. This species is characterized by a slightly offset labial region with three annuli, en face morphology belonging to Group II, lateral field with four incisures with two outer bands areolated as observed under a light microscope and the inner band also partially areolated at the vulva region as observed in scanning electron microscopy view, a robust stylet (14–17 μm) with rounded knobs and subcylindrical tail with annulated tail tip. This important and common species remained largely under the radar, probably due to identifications based only on sequence similarity, including mislabelled Pratylenchus bolivianus sequences in GenBank. Pathogenicity of P. vandenbergae stat. nov. in finger millet roots was confirmed through acid fuchsin staining, and reproduction and pathogenicity tests in maize, soybean, sunflower and tomato plants demonstrated its capacity to affect crop growth. Life cycle comparison with P. penetrans in vitro showed a similar life cycle length but significantly higher fecundity. Finally, significant differences in pathogenicity and reproduction of P. vandenbergae stat. nov. were found both at genotype level (finger millet genotypes OKHALE‐1 & KNE1034) and crop level (maize, soybean, sunflower and tomato plants).
Pratylenchus vandenbergae is recognized as a separate species. It was isolated from Kenya and South Africa, characterized using morphological and molecular techniques and its life cycle, fecundity and pathogenicity explained.
A survey was performed to detect the presence of cyst nematodes in the Cape Floristic Region of South Africa. Soil was collected in the rhizosphere of the dominant plant species within blocks of ...indigenous vegetation and cysts were extracted from them. A total of 81 blocks of indigenous vegetation were sampled as described. Cysts were detected in 7 of these samples, representing 6 different vegetation types. One set of primers was used to amplify the ITS regions from these cysts, including the 5.8S ribosomal gene, as well as short parts of the 18S and 28S ribosomal genes. ITS-rDNA sequences from the indigenous isolates were aligned with selected sequences of other species from the Heteroderidae. Phylogenetic analyses to resolve the relationships between indigenous isolates and selected representatives of the Heteroderidae were conducted using the Maximum Parsimony method. The consensus tree resulting from alignment of the circumfenestrate cysts revealed that isolates SK18, WK1 and WK26 are included in a clade of Globodera species that parasitise non-solanaceous plants, forming a monophyletic group with G. millefolii, G. artemisiae, and an unidentified Globodera sp. from Portugal. In a tree resulting from the alignment of the Heterodera spp., isolates OK14 and WK2 are included in the Afenestrata group, forming a monophyletic group with H. orientalis.This survey unearthed at least four potentially new species of cyst nematodes, which may prove invaluable for the study of the evolution and biogeography of the group.
Using a sand bioassay,
Steinernema yirgalemense gave 93% control of cocooned pupae and emerging moths at a concentration of 20
IJs/cm
2, 7
days after treatment. Moths infected with nematodes were ...able to emerge normally and to fly away from the sand surface, before being trapped in the surrounding container.
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► Six EPN species found during a survey of citrus orchards. ►
Steinernema yirgalemense reported from South Africa. ► Bioassays with nematodes using the soil stages of the false codling moth
Thaumatotibia leucotreta. ► Infection of emerging moths escaping from sand and aerial transport of nematodes shown.
A survey was conducted to determine the diversity and frequency of endemic entomopathogenic nematodes (EPN) in citrus orchards in the Western Cape, Eastern Cape and Mpumalanga provinces of South Africa. The main aim of the survey was to obtain nematodes as biological control agents against false codling moth (FCM),
Thaumatotibia leucotreta, a key pest of citrus in South Africa. From a total of 202 samples, 35 (17%) tested positive for the presence of EPN. Of these, four isolates (11%) were found to be steinernematids, while 31 (89%) were heterorhabditids. Sequencing and characterisation of the internal transcribed spacer (ITS) region was used to identify all nematode isolates to species level. Morphometrics, morphology and biology of the infective juvenile (IJ) and the first-generation male were used to support molecular identification and characterisation. The
Steinernema spp. identified were
Steinernema khoisanae,
Steinernema yirgalemense and
Steinernema citrae. This is the first report of
S. yirgalemense in South Africa, while for
S. citrae it is the second new steinernematid to be identified from South Africa.
Heterorhabditis species identified include
Heterorhabditis bacteriophora,
Heterorhabditis zealandica and an unknown species of
Heterorhabditis. Laboratory bioassays, using 24-well bioassay disks, have shown isolates of all six species found during the survey, to be highly virulent against the last instar of FCM larvae.
S. yirgalemense, at a concentration of 50
IJs/FCM larva caused 100% mortality and 74% at a concentration of 200
IJs/pupa. Using a sand bioassay,
S. yirgalemense gave 93% control of cocooned pupae and emerging moths at a concentration of 20
IJs/cm
2. This is the first report on the potential use of EPN to control the soil-borne life stages of FCM, which includes larvae, pupae and emerging moths. It was shown that emerging moths were infected with nematodes, which may aid in control and dispersal.
A new cyst nematode, herein described as Globodera agulhasensis n. sp., was found parasitising Senecio burchelli in the Western Cape Province, South Africa. Second-stage juveniles are characterised ...by a well developed stylet of 23.5 (22.5-24.8) μm with rounded to anteriorly flattened knobs. The dorsal pharyngeal gland outlet is 4.4 (3.5-6.5) μm posterior to the stylet knobs. The tail is 56 (49-64) μm long and the length of the hyaline region is 25 (19-29) μm. The cysts are characterised by their ovate to spherical shape, short neck, the presence of subcuticular punctations over the entire body and the absence of bullae or vulval bodies. Six to 12 cuticular ridges/lines are present on the outer surface of the cyst between the anus and vulval basin. Granek's ratio is 1.7 (1.0-3.0), the vulval basin diam. 17.6 (11.7-26.1) μm and the distance between vulval basin and anus is 28.6 (19.1-47.0) μm. Males have a stylet length of 26.1 (24.4-27.7) μm and spicule length of 30.3 (27.2-33.8) μm with a rounded tip. Females have a stylet length of 22.1 (19.0-24.4) μm, a large median bulb almost filling the body diam., and a short vulval slit 4.2 (3.2-6.6) μm long. Phylogenetic relationships of G. agulhasensis n. sp. with other species of the genus, inferred from ITS-rRNA sequences by using the neighbour-joining (NJ), maximum likelihood (ML) and maximum parsimony method (MP), indicate that G. agulhasensis n. sp. is included in the clade of Globodera sp. that parasitise non-solanaceous plants, forming a monophyletic group with unidentified Globodera spp. from Portugal, G. millefolii and G. artemisiae. For diagnostic purposes, three restriction enzymes, Hpy8I, RsaI and XceI were selected as being able to discriminate between G. agulhasensis n. sp. and other Globodera spp. present in South Africa.
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