Despite being the single largest cassava-producing country, yields in Nigeria remain consistently poor and among the lowest. Regionally, yields are also particularly low across Africa. Pests and pathogens, including plant-parasitic nematodes, play an important role in this current yield deficit. African countries are not only faced with the problem of food security but also that of nutritional deficiency, due to limited micronutrients in the diet. In this study, six biofortified cultivars were evaluated for their response to inoculation with approximately 30 000 root-knot nematode (Meloidogyne incognita) eggs in 30 l pots in Nigeria. All cassava cultivars proved highly susceptible to M. incognita infection after 6 months, with nematode reproduction factor ranging from 7.0 to 44.8. Galling was common on feeder roots and gall index scores were recorded between 4 to 5 (on a scale of 1-5 where 5 ⩽ 100 galls). Meloidogyne incognita infection significantly reduced plant height, stem girth, fresh plant mass, fresh storage root number and storage root weight. Percentage yield loss of between 41.8-88.4% was recorded in M. incognita-infected plants compared with non-infected controls. Although M. incognita reduced storage root weight, it did not necessarily affect the nutritional quality (total carotenoid) or dry weight percentage of the biofortified cassava cultivars. Total carotenoid and dry weight contents of the control cultivar were similar to some of the biofortified cultivars. The high susceptibility of the biofortified cassava cultivars to M. incognita infection indicates that substantial yield losses are likely being experienced by farmers, as this nematode pest is prevalent across sub-Saharan Africa and the tropics.
The root-lesion nematode, Pratylenchus penetrans, causes growth reduction in glasshouse-grown lettuce and is mainly controlled by chemical soil disinfestation. Integrated management strategies require more knowledge about the population dynamics and damage threshold densities. We monitored the population during 2.5 years in a commercial glasshouse by sampling soil in the same four 1 m2 spots at 0-30 cm and 30-60 cm depth. The grower grew lettuce in rotation with leek, applied 1,3-dichloropropene in summer and left the field fallow during winter. Growing leek reduced the nematode population slightly but chemical soil disinfestation lowered the numbers drastically, although 41% of the nematodes in the deeper layer survived. Black fallow resulted in a slight increase of the population, probably due to hatching. Two pot experiments with ten densities of P. penetrans were conducted to estimate the damage threshold for a summer and autumn cultivar (‘Cosmopolia’ and ‘Brighton’, respectively). The thresholds for lettuce weight were 669 and 3834 P. penetrans (100 ml soil)−1 in summer and autumn, respectively, but with considerable variability in estimated parameters. The thresholds for root damage were much lower: 204 and 48 P. penetrans (100 ml soil)−1. Nematode numbers did not increase on lettuce in the pot tests (maximum multiplication rate was 0.40) but increased slightly in the commercial setting. These results show that populations of P. penetrans build up slowly when butterhead lettuce is rotated with leek and fallow, but chemical soil disinfestation is required to avoid numbers resulting in root damage.
Within sub-Saharan Africa (SSA), although nematodes are viewed among the most important threats to crop production and food security, the presence of trained nematologists working within this discipline has traditionally been viewed as scarce. The few research studies concerning this subject address this topic from a country or sub-regional perspective and generally portray nematology as ‘insufficient’. Over the past two decades, a few initiatives have been instrumental in building greater nematology expertise. For the first time a structured survey was undertaken, involving interviews with individuals from SSA that were (or currently are) involved in nematology training programmes, research, national extension services or in African universities. This paper provides evidence of the positive impact of various initiatives and shows an increase in the number of available nematology positions, together with high rates of graduates that return home to occupy qualified positions. Our findings will help researchers, policy makers and donors to identify areas requiring support to increase the promotion of nematology in SSA and to make an impact for end-users.
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.
Bursaphelenchus rockyi n. sp., isolated in Peking, China, from peat moss imported from Russia, is described. It is characterised by a lateral field with four lines, excretory pore located at the base of the nerve ring or slightly posterior, spicule 15.9 (15.1-17.3) μm long along the chord and with high condylus and a rounded tip, rostrum triangular or conical with bluntly pointed tip, lamina curvature becoming more pronounced at 60% of total length, six caudal papillae with P3 and P4 adjacent to each other, bursa small, starting posterior to P4, vulval lips hemispherical and protruding, and tail conical with finely rounded or mucronated terminus. The new species belongs to the fungivorus-group and is most similar to B. arthuri, B. arthuroides, B. fungivorus and B. seani, but can be distinguished from related species by morphological and sequencing results.
Fumigants, such as 1,3-dichloropropene and chloropicrin, have become key to pre-plant pest management in almond production. Whilst the use of these fumigants has become increasingly restricted due to human health concerns, less is known about their below-ground non-target effects in orchards and how nematode communities recover from fumigation over time. In this study, replicated trials compared 1,3-dichloropropene + chloropicrin to non-treated controls in two almond orchards in California, USA. Nematode communities, nematode indices and nematode metabolic footprints were quantified soon after fumigation and for 2 years afterwards. Fumigation reduced the Herbivore Metabolic Footprint in year 1, and populations of Pratylenchus vulnus in year 3. Fumigation also reduced populations of larger omnivores and predators, resulting in lower levels of the Structure Index at one site. Populations of fungal-feeding nematodes were more adversely affected by fumigation than bacterial-feeding nematode populations. At both sites, fumigation still influenced nematode community composition 2 years after treatment application.
Hoplolaimus smokyensis n. sp. is a new species of lance nematode collected in Great Smoky Mountains National Park, USA. Females of H. smokyensis n. sp. have a labial region characterised by six, occasionally five, annules. The basal lip annule is subdivided by about 24 longitudinal striae. The stylet averages 47 μm long with robust, tulip-shaped stylet knobs bearing anterior projections. The hemizonid is ca 4 μm anterior to the excretory pore. The lateral field is incompletely areolated and has four continuous incisures from the metacorpus region to the tail region. There are three pharyngeal gland nuclei. Vulval epiptygma are absent. The scutellate phasmids are located one anterior and one posterior to the vulva. The male is shorter than the female and the head region is higher and more rounded than that of the female. The bursa extends to the tail tip and the gubernaculum is large and protrusible and has titillae and a capitulum. Morphologically, H. smokyensis n. sp. is most similar to H. galeatus and H. stephanus, but can be distinguished by differences such as the number of annules and longitudinal striae on the lip region and morphometric values. Hoplolaimus smokyensis n. sp. is also genetically distinct from other species according to comparisons of ribosomal and mitochondrial DNA sequences. Phylogenetic analyses based on ribosomal and mitochondrial gene sequences suggest that H. smokyensis n. sp. is a lineage distinct from related Hoplolaimus species.
Rapid diagnosis tools for detection of root-knot nematodes play an important role in the disease control and eradication programme. Recombinase polymerase amplification (RPA) assays were developed targeting the IGS rRNA gene of the pacara earpod tree root-knot nematode, Meloidogyne enterolobii. The RPA assays using TwistAmp® Basic and TwistAmp® exo kits allowed detection of M. enterolobii from gall tissues and crude nematode extracts of all stages of target species without a DNA extraction step. The results of real-time RPA assays using a real-time fluorescent detection of a series of crude nematode extracts showed reliable detection with sensitivity of 1/10 of a second-stage juvenile in a RPA reaction tube after 15-20 min. The RPA assay provides affordable, simple, fast and sensitive detection of M. enterolobii.
To fulfil different research purposes, five methods to inoculate Aphelenchoides besseyi onto seedlings and panicles of rice, Oryza sativa, were evaluated in this study and the efficiency of the inoculation methods assessed by success rates and recovery rates. Among the three methods leading to the infection of young seedlings without obvious mechanical wounds, i.e., water flotation, seed soaking and leaf spraying, the inoculation of 125 nematodes plant−1 by the water flotation method gave rise to the highest success rate and recovery rate, 95.6 and 8.3%, respectively, in growth chamber experiments. When conducted in the plastic house, seed soaking and leaf spraying of 125 nematodes plant−1 resulted in 75.6 and 66.7% success rate, respectively, and 155.7 and 178.1% recovery rates, respectively. The injection or spraying of 2000 nematodes panicle−1 at the booting or flowering stage gave 100% infection.
Nematodes respond to a multitude of environmental cues. For example, the social behaviours clumping and bordering were described as a mechanism of hyperoxia avoidance in Caenorhabditis elegans and Pristionchus pacificus. A recent study in P. pacificus revealed a novel regulatory pathway that inhibits social behaviour in a response to an as yet unknown environmental cue. This environmental signal is recognised by ciliated neurons, as mutants defective in intraflagellar transport (IFT) proteins display social behaviours. The IFT machinery represents a large protein complex and many mutants in genes encoding IFT proteins are available in C. elegans. However, social phenotypes in C. elegans IFT mutants have never been reported. Here, we examined 15 previously isolated C. elegans IFT mutants and found that most of them showed strong social behaviour. These findings indicate conservation in the inhibitory mechanism of social behaviour between P. pacificus and C. elegans.