Little information is available for nematode pests associated with watermelon in sub-Saharan Africa (SSA). This study recorded the abundance and prevalence of plant-parasitic nematodes from 25 localities across south-west Nigeria during 2016/2017. Of the 11 nematode species identified, those belonging to Meloidogyne spp. were predominant according to Prominence Values, followed by Helicotylenchus dihystera, Pratylenchus zeae and Scutellonema bradys. Morphological and molecular analyses revealed the identity of four species of root-knot nematodes: Meloidogyne enterolobii, M. incognita, M. javanica and M. arenaria (in descending order of abundance and occurrence). Meloidogyne arenaria is reported for the first time from south-west Nigeria, while S. bradys and Xiphinema nigeriense are first reports for watermelon. Significant associations were observed between the frequency of occurrence of the predominant nematode species and soil properties as well as rainfall. Results provide baseline information on the nematode pest occurrence on watermelon in Nigeria and in a wider context for SSA.
Aphelenchoides smolae n. sp. isolated in Ningbo Port, China, from medium soil and tissues of Lilium orientalis bulbs imported from The Netherlands, is described. It is characterised by the female body length of 826 (672-1002) μm and male body length of 785 (683-844) μm, lateral field with four lines (three bands), stylet 13.0-14.9 μm long with small basal swellings, excretory pore situated slightly posterior to nerve ring, vulval flap absent, post-vulval uterine sac well developed and extending for ca 35.7-62.4% of vulva to anus distance, conical tail with terminus bearing a single mucron with many tiny nodular protuberances under SEM, males common, with spicules 25.7-29.8 μm long (median curved line), the condylus and rostrum rounded, well developed, the dorsal limb with a hook-like tip, and tail bearing three pairs (2 + 2 + 2) of caudal papillae and a sharply pointed mucron. The new species belongs to the Group 2 category of Aphelenchoides species sensu Shahina. Phylogenetic analysis based on 18S, 28S D2-D3 of rDNA and COI mtDNA further characterised the new species.
Cryptaphelenchus paravaricaudatus n. sp., from declining Pinus massoniana in China, is described and illustrated. The new species is characterised by the 233-308 μm long females with distinctly annulated cuticle, lateral fields with four lines, lip region separated from the body by a shallow depression, delicate stylet with small knobs, post-vulval uterine sac short and rectum and anus invisible. Males are 204-259 μm long, with spicules 8.5-12.0 μm long, condylus well developed and broad, caudal papillae arranged as a single (P1) and a pair of precloacal papillae (P2) plus two pairs of postcloacal papillae (P3 and P4). Based upon the general morphology of the female, the new species most closely resembles C. varicaudatus. The morphological differences with the aforementioned species and other species having similar morphology are discussed. The phylogenetic analyses based on small (SSU) and large subunit (LSU) D2-D3 expansion segments of ribosomal DNA (rDNA) of different individuals of the new species revealed that it fell into the clade of Cryptaphelenchus in both SSU and LSU trees. The monophyly of the genus was retained.
The endomigratory root-lesion nematode, Pratylenchus scribneri, is one of the major plant-parasitic nematodes infecting potato. Accurate identification and quantification of this nematode are essential to develop management strategies but microscopic observations are particularly challenging and time consuming. In this study, a SYBR Green I-based real-time quantitative polymerase chain reaction (qPCR) assay was developed to detect and quantify P. scribneri from field soil DNA extracts. A primer set was designed from the internal transcribed spacer (ITS) region of the P. scribneri rDNA gene. Primer specificity to the target nematode was evaluated by both in silico analysis and qPCR and no detection or non-specific amplification was observed for other non-target nematode species/communities tested in this study. Standard curves were generated using DNA extracts from autoclaved soil infested with varying nematode numbers for calibration. The curves were supported by a high correlation between the P. scribneri numbers artificially added to soil or estimated from naturally infested field soils by traditional methods, and the numbers quantified using the qPCR assay. The assay was able to detect 1 out of 128 (0.0078) equivalents of the DNA of a single nematode in 0.5 g of soil. The qPCR assay developed in this study provides a specific and sensitive detection and quantification of P. scribneri from field soils and a rapid alternative to time-consuming traditional nematode identification and enumeration.
Nematode parasitism is a yield limiting factor in many cropping systems, including potato production, which can translate into substantial economic losses. These impacted financial returns are simply calculated by subtracting the cost of production from total revenue (yield times the price per yield of potatoes). The production costs can include, but are not limited to, chemical and biological control agents. To assess economic returns associated with different nematode management strategies, we evaluated complete cost estimations for a representative commercial potato farm in central Michigan, USA. Economic returns were calculated using stochastic parameters for two biological control agents (MeloCon and Majestene), six chemical controls (Mocap, Movento, Nimitz, Velum and Vydate), and two soil amendments (poultry and dairy manure). Evaluated costs included stochastic estimations for price per unit weight of potatoes, fuel, labour and production land rent. Yield data from three field trials were used to create empirical distributions. Using yield data and stochastic cost estimations, we generated 500 simulations of net returns per treatment. The top three average returns were obtained from the use of Mocap, Nimitz and poultry manure. Velum, Movento, dairy manure and Vydate also gave returns significantly higher than no treatment at all; however, the biological nematicide, Majestene, showed negative returns. This simple financial model is a crucial layer of analysis on the performance of nematicides that can be adapted to advise growers through Agricultural Extension activities and needs to include the evaluation of biological control agents.
A population of Hemicriconemoides phoenicis was recovered from Khuzestan province, south-western Iran, in association with date palm. The recovered population was characterised by 518-645 μm long females having a 76-82 μm long stylet, rounded to oblong spermatheca filled with sperm, a 28.0-39.8 μm long tail, juveniles common, with 14 longitudinal rows of rounded scales, and males absent. Compared to the original data, no morphological and morphometric differences were observed. In molecular phylogenetic analyses using the D2-D3 expansion segments of the 28S rRNA gene and a near-full-length fragment of the 18S rRNA gene sequences using Bayesian inference (BI) and maximal number of species of the genus, the two newly generated 28S sequences of the Iranian population formed a maximally supported clade with two original sequences of the species; and the 18S sequence formed a maximally supported clade with an unidentified isolate of the genus in the corresponding phylogeny. This is the second report of the species since its original description, Iran representing a new geographical record and supporting the suggestion that date palm could be its preferred host.
A new nematode species was recovered from the syconia of Ficus semicordata from Xishuangbanna Tropical Botanical Garden, Yunnan Province, China. It is described herein as Martininema semicordatae n. sp. and is characterised by having the combined characters of a long post-vulval uterine sac, excretory pore located at nerve ring level, amoeboid sperm, three pairs of subventral papillae on the male tail, rounded male tail tip with mucron, absence of gubernaculum (= apophysis), and a recurved, rose-thorn-shaped spicule lacking a terminal cucullus. Martininema semicordatae n. sp. differs from other sequenced species by differences in the partial small subunit (SSU) rRNA gene and D2-D3 expansion segments of the large subunit (LSU) rRNA gene. Phylogenetic analysis with LSU D2-D3 expansion segment sequences suggested that M. semicordatae n. sp. is clustered in a highly supported monophyletic clade with M. guangzhouense, M. fistulosus and M. baculum, and shares a common ancestor with these three species.
In this study, we provide morphological and molecular characterisation of three known species of the Criconematoidea, namely Criconema cylindraceum, Paratylenchus alleni and P. steineri, recovered from Iran. Descriptions, morphometric data, drawings and photomicrographs are provided, and comparisons are made with closely related species. Phylogenetic analysis using the D2-D3 expansion segments of the 28S rRNA gene revealed that C. cylindraceum formed a cluster with Ogma decalineatus, a species with a similar head structure, but with differences in cuticle ornamentation, tail shape and morphometric characters. Moreover, P. alleni grouped with species of Paratylenchus having four lateral lines and a short stylet (< 40 μm), exceptionally including the unresolved P. straeleni, while P. steineri formed a clade with long stylet species, including P. teres and P. wuae. The taxonomic placement of C. cylindraceum in Criconema, rather than in Criconemoides, is justified, and P. teres is molecularly differentiated from P. steineri, the two species differing in having or lacking a stylet in the fourth-stage juvenile.
Members of the family Leptolaimidae are reported for the first time from Iran with description of two new species of Leptolaimus from the Persian Gulf in the south of the country. Leptolaimus hormozganensis sp. n. is described based upon three populations. It differs from other Leptolaimus species in the position of the pharyngeal supplement and the number of precloacal tubular supplements and has a single sickle-shaped tubular pharyngeal supplement at mid-pharynx level in both sexes, 9-12 male precloacal supplements and one female preanal supplement. Leptolaimus dimorphus sp. n. is characterised by the presence of a pharyngeal tubular supplement only in some adults, one female preanal supplement and four male precloacal supplements. It differs from other species in that the pharyngeal supplement is only present in some specimens, presence of four male precloacal supplements, tail 50-59 μm long and ventrosublateral position of vulva on either the right or left side of the body. Near full length SSU rDNA sequences are provided for L. hormozganensis sp. n. and two different males (one with, and one without, a pharyngeal supplement) of L. dimorphus sp. n. COI sequences for three populations of L. hormozganensis sp. n. from different regions of the Persian Gulf are also obtained. New sequences of two Leptolaimus species formed a clade with other sequenced Leptolaimus spp. and representatives of two genera of Leptolaimidae, i.e., Aphanolaimus and Paraplectonema in a phylogeny based on SSU rDNA gene with 1.00/81 Bayesian posterior probability/maximum likelihood bootstrap (BPP/BS) values. Molecular phylogeny confirmed the synonymy of Leptolaimus and Halaphanolaimus that was formerly proposed based only on morphology. Based on SSU sequences and morphological characters, the presence of a pharyngeal supplement may not be a species-specific character and should not be used to differentiate genera.
A new species of entomopathogenic nematode, Steinernema riojaense n. sp., was isolated during a survey in La Rioja province of Spain. Morphological and morphometric traits place the new species in the glaseri-group, which is characterised by having the largest infective juvenile (IJ) with an average body length in excess of 1000 μm. The IJ of S. riojaense n. sp. possess a body length of 1043 (869-1172) μm, the lateral fields are formed by eight equally spaced and developed ridges (nine incisures) in the mid-body region, giving the formula 2, 6, 8, 4, the excretory pore is located posterior to the mid-pharynx region (D% = 58), and the hyaline region occupies ca half of the tail length. The male spicules are moderately curved with a sharp tip and are golden-brown in colour with the manubrium elongate and having a length to width ratio of 1.7:1. The first-generation male tail is non-mucronate, whereas a small papilla-like mucron is developed in the second generation. There are 11 pairs of genital papillae plus a single precloacal papilla. The first-generation female possesses a moderately protruding vulva and a slightly protruding postanal swelling. The second-generation female possesses a slightly protruding vulva and a postanal swelling. The new species is further characterised by sequences of the internal transcribed spacer (ITS) and partial 28S regions (D2-D3) of the ribosomal DNA (rDNA). Phylogenetic analyses confirm that S. riojaense n. sp. belongs to the glaseri-group and forms a monophyletic subclade with other European species.