Integrative taxonomy of Mesocriconema onoense (Tylenchida: Criconematidae) from Vietnam highly suggests the synonymization of Mesocriconema brevistylus and related species.

The genus Mesocriconema is one of the most diverse genera within the family Criconematidae, known as ring nematodes, with more than 90 species. Although species in this genus usually show distinct morphological characterizations, the identification based only on morphology can lead to misidentification in many studies resulted in a number of synonymizations in the genus over time. In this study, an integrated approach has been applied in characterizing Mesocriconema onoense from Vietnam. The molecular data of 28S rRNA, ITS, 18S rRNA regions were analyzed and discussed to confirm the correct names on GenBank. Besides, phylogenetic analyses of 28S rRNA, ITS, and 18S rRNA regions of Mesocriconema species revealed that Mesocriconema brevistylus should be considered as a junior synonym of M. onoense. Consequently, M. helicus, M. onostris, and M. paronostris should also be considered as the synonyms of M. onoense.

The genome of the migratory nematode, Radopholus similis, reveals signatures of close association to the sedentary cyst nematodes.

Radopholus similis, commonly known as the burrowing nematode, is an important pest of myriad crops and ornamentals including banana (Musa spp.) and Citrus spp. In order to characterize the potential role of putative effectors encoded by R. similis genes we compared predicted proteins from a draft R. similis genome with other plant-parasitic nematodes in order to define the suite of excreted/secreted proteins that enable it to function as a parasite and to ascertain the phylogenetic position of R. similis in the Tylenchida order. Identification and analysis of candidate genes encoding for key plant cell-wall degrading enzymes including GH5 cellulases, PL3 pectate lyases and GH28 polygalactouranase revealed a pattern of occurrence similar to other PPNs, although with closest phylogenetic associations to the sedentary cyst nematodes. We also observed the absence of a suite of effectors essential for feeding site formation in the cyst nematodes. Clustering of various orthologous genes shared by R. similis with other nematodes showed higher overlap with the cyst nematodes than with the root-knot or other migratory endoparasitic nematodes. The data presented here support the hypothesis that R. similis is evolutionarily closer to the cyst nematodes, however, differences in the effector repertoire delineate ancient divergence of parasitism, probably as a consequence of niche specialization. These similarities and differences further underscore distinct evolutionary relationships during the evolution of parasitism in this group of nematodes.

First Morphological and Molecular Report of Aphelenchoides blastophthorus on Strawberry Plants in Switzerland.

Foliar nematodes represent a minor feeding group within the genus Aphelenchoides Fischer, 1894. The facultative plant parasitic species A. blastophthorus can cause crinkling of leaves, reduced vigor, and stunting of agricultural and ornamental plants. Here we report the first finding of A. blastophthorus in leaves, crowns, and roots of strawberry plants collected in Switzerland in 2018. Species identification was confirmed by morphological and morphometric characterization supported by molecular barcoding of 18S ribosomal RNA (18S), 28S ribosomal RNA (28S), and cytochrome c oxidase I (COI) gene fragment analyses. Phylogenetic analysis of 18S indicated that A. blastophthorus was grouped within close distance to A. fragariae, a well-known foliar nematode affecting strawberry plants. Furthermore, the newly generated molecular barcodes of the partial 28S and COI of A. blastophthorus will support species identification in the future.

Multigene phylogeny of root-knot nematodes and molecular characterization of Meloidogyne nataliei Golden, Rose & Bird, 1981 (Nematoda: Tylenchida).

The root-knot nematodes of the genus Meloidogyne are highly adapted, obligate plant parasites, consisting of nearly one hundred valid species, and are considered the most economically important group of plant-parasitic nematodes. Six Meloidogyne species: M. arenaria, M. hapla, M. incognita, M. microtyla, M. naasi and M. nataliei were previously reported in Michigan, USA. For this study, Meloidogyne nataliei was isolated from the grapevine Vitis labrusca from the type locality in Michigan, USA, and was characterized using isozyme analysis and ribosomal and mitochondrial gene sequences. No malate dehydrogenase activity was detected using macerate of one, five, six, seven or ten females of M. nataliei per well. However, one strong band (EST = S1; Rm: 27.4) of esterase activity was detected when using homogenates of ten egg-laying females per well. Phylogenetic analyses of sequences of the partial 18S ribosomal RNA, D2-D3 of 28S rRNA, internal transcribed spacer of rRNA, mitochondrial cytochrome oxidase subunit I genes and the cytochrome oxidase subunit II-16S rRNA intergeneric fragment from fifty-five valid Meloidogyne species and M. nataliei were conducted using Bayesian inference and maximum likelihood methods. From these results, we infer 11 distinct clades among studied species, with M. nataliei and M. indica composing a basal lineage. Seventy five percent of these species belong to seven clades within the Meloidogyne superclade. Characterization of these clades is provided and evolutionary trends within the root-knot nematodes are discussed.

The first report of Xenorhabdus indica from Steinernema pakistanense: co-phylogenetic study suggests co-speciation between X. indica and its steinernematid nematodes.

During a survey in agricultural fields of the sub-humid region of Meerut district, India, two strains of entomopathogenic nematodes, labelled CS31 and CS32, were isolated using the Galleria baiting technique. Based on morphological and morphometric studies, and molecular data, the nematodes were identified as Steinernema pakistanense, making this finding the first report of this species from India. For the first time, we performed a molecular and biochemical characterization of the bacterial symbiont of S. pakistanense. Furthermore, a co-phylogenetic analysis of the bacteria from the monophyletic clade containing a symbiont of S. pakistanense, together with their nematode hosts, was conducted, to test the degree of nematode-bacteria co-speciation. Both isolates were also tested in a laboratory assay for pathogenicity against two major pests, Helicoverpa armigera and Spodoptera litura. The morphology of the Indian isolates corresponds mainly to the original description, with the only difference being the absence of a mucron in first-generation females and missing epiptygmata in the second generation. The sequences of bacterial recA and gyrB genes have shown that the symbiont of S. pakistanense is closely related to Xenorhabdus indica, which is associated with some other nematodes from the 'bicornutum' group. Co-phylogenetic analysis has shown a remarkable congruence between the nematode and bacterial phylogenies, suggesting that, in some lineages within the Steinernema / Xenorhabdus complex, the nematodes and bacteria have undergone co-speciation. In the virulence assay, both strains caused a 100% mortality of both tested insects after 48 h, even at the lowest doses of 25 infective juveniles per insect, suggesting that S. pakistanense could be considered for use in the biocontrol of these organisms in India.

Molecular and morphological characterization of Paurodontoides siddiqii n. sp. (Nematoda: Hexatylina, Sphaerulariidae) associated with bark samples of Pinus eldarica from western Iran.

A new species of Paurodontoides, P. siddiqii n. sp., is described and illustrated based on its morphological, morphometric, and molecular characters. The new species is characterized by a female 550-729 µm long, lip region continuous with body contour, stylet length 7.0-8.0 µm long or c. 1.0-1.2 times the lip region diameter, lateral fields with four smooth incisures, excretory pore at 85-125 µm from anterior end located at the base of the pharyngeal bulb or posterior to it, basal pharyngeal bulb with a short posterior extension projecting into the intestine, monodelphic-prodelphic reproductive system with prominent 19-22 µm long post-uterine sac, and elongate conoid tail with a filiform terminus. The new species is compared with two known species of the genus. It differs from the type species of the genus, P. linfordi, by having slightly shorter stylet, lateral field with smooth incisures, different position of the excretory pore, and absence of male. Compared to P. latus, the new species has a shorter body, shorter stylet, different position of the excretory pore, female tail shape and absence of male. The new species was also compared with close species of the genus Paurodontus because of lateral field marked with four lines, asymmetrical stylet knobs and absence of male. Molecular phylogenetic studies of the new species using partial sequences of 18S rDNA revealed that it forms a clade with a species of the genus Ficotylus. In phylogenetic analyses using partial sequences of the 28S rDNA D2-D3 domain, the new species formed a monophyletic group with a species of the genus Veleshkinema and Sphaerularia spp. (Sphaerulariinae).

Coinvasion by the ladybird Harmonia axyridis (Coleoptera: Coccinellidae) and its parasites, Hesperomyces virescens (Ascomycota: Laboulbeniales) and Parasitylenchus bifurcatus (Nematoda: Tylenchida, Allantonematidae), in the Caucasus.

The study of parasites in recently established populations of invasive species can shed light on the sources of invasion and possible indirect interactions between the alien species and native ones. We studied parasites of the global invader Harmonia axyridis (Coleoptera: Coccinellidae) in the Caucasus. In 2012, the first established population of Ha. axyridis was recorded in the Caucasus in Sochi (south of European Russia, Black Sea coast). By 2018, the ladybird had spread to a vast area: Armenia, Georgia and south Russia (Adygea, the Krasnodar territory, the Stavropol territory, Dagestan, Kabardino-Balkaria and North Ossetia). The examination of 213 adults collected in Sochi in 2018 showed that 53% were infested with Hesperomyces virescens fungi (Ascomycota: Laboulbeniales) and that 8% were infested with Parasitylenchus bifurcatus nematodes (Nematoda: Tylenchida, Allantonematidae). The examined Ha. axyridis specimens were free of the parasitic mite Coccipolipus hippodamiae. An analysis of the phylogenetic relationships of P. bifurcatus based on 18S rDNA confirmed the morphological identification of this species. Hesperomyces virescens and P. bifurcatus were first recorded in the Caucasus and Russia, although they are rather widespread in Europe. This likely indicates that they appeared as a result of coinvasion with their host because the populations of Ha. axyridis, He. virescens and P. bifurcatus in the Caucasus are isolated from the main parts of the ranges of these species in Europe. The nearest localities of Ha. axyridis is on another shore of the Black Sea, and the nearest localities of He. virescens and P. bifurcatus are more than 1000 km from the Caucasus. It is impossible to determine whether the first founders of the Caucasian population were infested with the parasites or whether the parasites were introduced by specimens of Ha. axyridis that arrived later from Europe. Harmonia axyridis was released in the region for pest control, but laboratory cultures are always free of He. virescens and P. bifurcatus. Therefore, the detection of He. virescens and P. bifurcatus indicates that the population of Ha. axyridis in the Caucasus could not have derived exclusively from released specimens. We did not find He. virescens on 400 specimens of 29 other ladybird species collected from the same localities as Ha. axyridis in the Caucasus. No reliable correlation between infestation by He. virescens and that by P. bifurcatus has been found. In addition to these two parasites, an unidentified species of the order Mermithida was recorded. This is the first documented case of Ha. axyridis infestation by a parasitic nematode of this order in nature.

Characterization of soil nematode communities in three cropping systems through morphological and DNA metabarcoding approaches.

We used complementary morphological and DNA metabarcoding approaches to characterize soil nematode communities in three cropping systems, conventional till (CT), no-till (NT) and organic (ORG), from a long-term field experiment. We hypothesized that organic inputs to the ORG system would promote a more abundant nematode community, and that the NT system would show a more structured trophic system (higher Bongers MI) than CT due to decreased soil disturbance. The abundance of Tylenchidae and Cephalobidae both showed positive correlations to soil organic carbon and nitrogen, which were highest in the ORG system. The density of omnivore-predator and bacterial-feeding nematodes was reduced in NT soils compared to CT, while some plant-parasitic taxa increased. NT soils had similar Bongers MI values to CT, suggesting they contained nematode communities associated with soils experiencing comparable levels of disturbance. Metabarcoding revealed within-family differences in nematode diversity. Shannon and Simpson's index values for the Tylenchidae and Rhabditidae were higher in the ORG system than CT. Compared to morphological analysis, metabarcoding over- or underestimated the prevalence of several nematode families and detected some families not observed based on morphology. Discrepancies between the techniques require further investigation to establish the accuracy of metabarcoding for characterization of soil nematode communities.

Nematode parasites of Duttaphrynus stomaticus (Lutken, 1864) (Amphibia: Anura) with description of a new species of Rhabdias Stiles and Hassall, 1905 (Nematoda: Rhabdiasidae) from Dehradun (Uttarakhand), India.

Rhabdias stomatica sp. nov. from the lungs of Duttaphrynus stomaticus (Lutken, 1864) from Dehradun, Uttarakhand, India is described and illustrated. Rhabdias stomatica sp. nov. is the 16th species described from the Oriental biogeographical region and the 8th species from India. The new species is differentiated from the closely related Oriental species in having 4 weakly developed lips, a trapezoidal shaped buccal cavity, different position of nerve ring and in the esophagus/body length ratio. In addition, to the new species found in the lungs, mature specimens of Aplectana macintoshii (Stewart, 1914) Travassos, 1931 and larvae representing two unidentified species of nematode were found in the large intestine of the D. stomaticus.

Molecular and morphological characterisation of Rhabdias picardiae Junker, Lhermitte-Vallarino et Bain, 2010 (Nematoda: Rhabdiasidae) from Delaland's River Frog, Amietia delalandii (Duméril et Bibron, 1841) (Amphibia: Pyxicephalidae) in South Africa.

Rhabdias picardiae previously known from the Guttural Toad, Sclerophrys gutturalis (Bufonidae) is described from a new host, Delaland's River Frog, Amietia delalandii (Pyxicephalidae). The species identification is confirmed by analysis of the COI gene sequence and morphological comparison with the original description. Morphological details of apical structures in adult parasitic R. picardiae, namely, the shape and position of lips, the number and position of external labial papillae, and the buccal capsule morphology are described using light and scanning electron microscopy. The buccal capsule width and length, the distance from anterior end to nerve ring and excretory pore, and ratios of distance to vulva to body length and body length to width were identified as less variable metrical characters in the studied sample of 30 specimens. Adult specimens demonstrated differences in the position of lips in relation to the oral opening and position of the buccal capsule in relation to the oesophagus depending on the size (age) of worms. The infective larvae of R. picardiae are described for the first time and characterised by two lateral alae consisting of two ridges, triangular pseudolabia with rounded tops, and presence of ornamentation on the rounded tail tip.

Description of two new species of Seinura Fuchs, 1931 (Nematoda: Aphelenchoididae) from Iran.

Two new species of Seinura are described and illustrated using both morphological and molecular characters. Seinura persica n. sp. is characterized by having females with a distinct cephalic region, stylet 19.5 (18-20) µm long, four incisures in the lateral fields, position of excretory pore anterior to the base of metacorpus, post-uterine sac 54.8 (50-60) µm long, and an elongate-conoid tail with a shallow depression on the dorsal side ending in a sharply pointed tip. Males have body length of 467 and 592 µm, spicules 15 and 16 µm long with a prominent triangular-shaped rostrum, developed condylus and no cucullus. Seinura hyrcania n. sp. is characterized by having an offset lip region, stylet 21.5 (18-24) µm long, three incisures in the lateral fields, excretory pore anterior to the base of the metacorpus, post-uterine sac 19 (12-25) µm long and conical tail ending in a filiform terminus. Morphological and morphometric diagnostic characters together with molecular data based on partial sequences of SSU and LSU of the ribosomal DNA gene are provided for these new species.

Versatile glycoside hydrolase family 18 chitinases for fungi ingestion and reproduction in the pinewood nematode Bursaphelenchus xylophilus.

The glycoside hydrolase family 18 (GH18) of chitinases is a gene family widely expressed in archaes, prokaryotes and eukaryotes, and hydrolyzes the ß-1,4-linkages in chitin. The pinewood nematode Bursaphelenchus xylophilus is one of the organisms that produces GH18 chitinases. Notably, B. xylophilus has a higher number of GH18 chitinases compared with the obligate plant-parasitic nematodes Meloidogyne incognita and Meloidogyne hapla. In this study, seven GH18 chitinases were identified and cloned from B. xylophilus based on genomic analyses. The deduced amino acid sequences of all these genes contained an N-terminal signal peptide and a GH18 catalytic domain. Phylogenetic analysis showed that the origin of B. xylophilus GH18 chitinases was independent of those from fungi and bacteria. Real-time quantitative reverse transcription PCR analysis indicated that GH18 chitinase genes had discrete expression patterns, representing almost all the life stages of B. xylophilus. In situ hybridisation showed that the mRNA of GH18 chitinase genes of B. xylophilus were detected mainly in the spermatheca, esophageal gland cells, seminal vesicle and eggs. RNA interference (RNAi) results revealed different roles of GH18 chitinase genes in B. xylophilus. Bx-chi-1, Bx-chi-2 and Bx-chi-7 were associated with reproduction, fungal cell-wall degradation and egg hatching, respectively. Bx-chi-5 and Bx-chi-6 may be involved in sperm metabolism. In conclusion, this study demonstrates that GH18 chitinases have multiple functions in the life cycle of B. xylophilus.

Species discovery and diversity in Lobocriconema (Criconematidae: Nematoda) and related plant-parasitic nematodes from North American ecoregions.

There are many nematode species that, following formal description, are seldom mentioned again in the scientific literature. Lobocriconema thornei and L. incrassatum are two such species, described from North American forests, respectively 37 and 49 years ago. In the course of a 3-year nematode biodiversity survey of North American ecoregions, specimens resembling Lobocriconema species appeared in soil samples from both grassland and forested sites. Using a combination of molecular and morphological analyses, together with a set of species delimitation approaches, we have expanded the known range of these species, added to the species descriptions, and discovered a related group of species that form a monophyletic group with the two described species. In this study, 148 specimens potentially belonging to the genus Lobocriconema were isolated from soil, individually measured, digitally imaged, and DNA barcoded using a 721 bp region of cytochrome oxidase subunit 1 (COI). One-third of the specimens were also analyzed using amplified DNA from the 3' region of the small subunit ribosomal RNA gene (18SrDNA) and the adjacent first internal transcribed spacer (ITS1). Eighteen mitochondrial haplotype groups, falling into four major clades, were identified by well-supported nodes in Bayesian and maximum likelihood trees and recognized as distinct lineages by species delimitation metrics. Discriminant function analysis of a set of morphological characters indicated that the major clades in the dataset possessed a strong morphological signal that decreased in comparisons of haplotype groups within clades. Evidence of biogeographic and phylogeographic patterns was apparent in the dataset. COI haplotype diversity was high in the southern Appalachian Mountains and Gulf Coast states and lessened in northern temperate forests. Lobocriconema distribution suggests the existence of phylogeographic patterns associated with recolonization of formerly glaciated regions by eastern deciduous forest, but definitive glacial refugia for this group of plant parasitic nematodes have yet to be identified. Unlike agricultural pest species of plant-parasitic nematodes, there is little evidence of long-distance dispersal in Lobocriconema as revealed by haplotype distribution. Most haplotype groups were characterized by low levels of intragroup genetic variation and large genetic distances between haplotype groups. The localization of nematode haplotypes together with their characteristic plant communities could provide insight into the historical formation of these belowground biotic communities.

Description of Cryptaphelenchus iranicus n. sp. (Nematoda: Ektaphelenchinae) recovered from bark samples of Pinus nigra from Iran.

Cryptaphelenchus iranicus n. sp., recovered from bark and wood samples of a weakened Pinus nigra in Kermanshah Province, western Iran, is described. The new species has females with body length of 250-330 µm and males 230-275 µm long, lip region set-off from body contour, 7-8 µm long stylet with small basal swellings, excretory pore located at 1.5-2.0 body diam. posterior to median bulb, post-vulval uterine sac short, 7-10 µm long and conical female posterior body end (tail) ending to a pointed tip. Males of the new species have seven (1+2+2+2) caudal papillae and a short mucro at tail tip. Based on morphological characters, the new species is close to C. cirrus, C. latus and C. leptocaudus. Phylogenetic analyses using the D2/D3 fragment of 28S rDNA show the new species forming a clade with other Cryptaphelenchus species with maximal (1.00) Bayesian posterior probability (BPP) in Bayesian inference and 100% bootstrap value (BS) in the maximum likelihood method. The Cryptaphelenchus clade forms a monophyletic group with members of subfamily Ektaphelenchinae.

Protein markers of Bursaphelenchus xylophilus Steiner & Buhrer, 1934 (Nickle, 1970) populations using quantitative proteomics and character compatibility.

The Pine Wood Nematode (PWN) Bursaphelenchus xylophilus is a severe forest pathogen in countries where it has been introduced and is considered a worldwide quarantine organism. In this study, protein markers for differentiating populations of this nematode were identified by studying differences among four selected Iberian and one American population. These populations were compared by quantitative proteomics (iTRAQ). From a total of 2860 proteins identified using the public database from the B. xylophilus genome project, 216 were unambiguous and significantly differentially regulated in the studied populations. Comparisons of their pairwise ratio were statistically treated and supported in order to convert them into discrete character states, suggesting that 141 proteins were not informative as population specific markers. Application of the Character Compatibility methodology on the remaining 75 proteins (belonging to families with different biological functions) excludes 27 which are incompatible among them. Considering only the compatible proteins, the method selects a subset of 30 specific unique protein markers which allowed the compared classification of the Iberian isolates. This approach makes it easier search for diagnostic tools and phylogenetic inference within species and populations of a pathogen exhibiting a high level of genetic diversity.

A new stem nematode, Ditylenchus oncogenus n. sp. (Nematoda: Tylenchida), parasitizing sowthistle from Adriatic coast dunes in southern Italy.

Morphological and molecular analyses of a stem nematode causing a severe disease on infected sowthistle (Sonchus bulbosus) plants, involving the formation of gall-like structures on infected leaves and stems, have led to the description of a new species named Ditylenchus oncogenus n. sp. Morphologically, the new species is characterized by a medium to large body size (all adults more than 1 mm in length); a delicate stylet (9.0-11.0 µm long) with minute, rounded knobs; a long post-vulval uterine sac (c. 65% of the vulva-anus distance); six incisures at the lateral fields and characteristic D. destructor-pattern of spicules (with pronounced ventral tumulus and anteriorly pointed, less sclerotized, cuticle parts present within the lamina). The results of molecular analysis of rRNA gene sequences, including the D2-D3 expansion regions of 28S rRNA, internal transcribed spacer (ITS) rRNA, partial 18S rRNA gene, the protein-coding mitochondrial gene, cytochrome oxidase c subunit I (COI), and the heat-shock protein 90 (hsp90) gene, support the new species status. The results of a host-suitability test indicated that the new species does not parasitize potato (Solanum tuberosum) tubers and broad bean (Vicia faba) seedlings. Histopathological observations on naturally infected sowthistle tissues revealed that D. oncogenus n. sp. causes floral stem neoplasia and midrib leaf gall formation on the type, and to date only known, host. The galls were characterized by extensive hyperplasia, where several necrotic cells in the neoplasic area were directly damaged by feeding of the nematode, whereas a number of adjacent cells showed typical cytological changes, such as granulated cytoplasm with hypertrophied nuclei and nucleoli.

Molecular and morphological characterization of Veleshkinema iranicum n. gen., n. sp. (Nematoda: Hexatylina, Sphaerularioidea) from Iran.

Veleshkinema  iranicum n. gen., n. sp. is described and illustrated based on morphological, morphometric and molecular characters. The new genus is characterized by having slender females and males, stylet with asymmetrical knobs, dorsal gland orifice just posterior to subventral knob, lip region with flattened apex and eight sectors, pharynx with a non-muscular and non-valvular median bulb, pharyngeal glands slightly overlapping intestine dorsally, visible cellular cardia, female with a single gonad having a quadricolumellate crustaformeria with 8-10 cells in each column, no postvulval uterine sac and rounded and offset spermatheca containing spheroid sperm cells, males with arcuate tylenchoid spicules and subterminal bursa. The new genus is morphologically compared with four genera: Abursanema, Deladenus, Prothallonema and Sphaerularia. Molecular phylogenetic studies of the new genus using 808 bp partial sequences of SSU ribosomal RNA gene placed the new genus in a clade with Sphaerularia spp. In phylogenetic analyses using 756 bp partial sequences of the 28S ribosomal RNA gene (D2-D3 segments), the new genus formed a monophyletic group with Abursanema iranicum and Sphaerularia spp.

An updated list of the plants associated with plant-parasitic Aphelenchoides (Nematoda: Aphelenchoididae) and its implications for plant-parasitism within this genus.

Few Aphelenchoides spp. are facultative plant-parasites (foliar and bulb nematodes); three of them are well known in agricultural systems, namely Aphelenchoides besseyi, A. fragariae and A. ritzemabosi. Ten other plant-parasitic species, A. arachidis, A. bicaudatus, A. blastophthorus, A. dalianensis, A. ensete, A. nechaleos, A. paranechaleos, A. saprophilus, A. sphaerocephalus and A. subtenuis, have been reported from a limited number of plant species. We compiled a new database of the associated plants for these thirteen species, a comprehensive list that includes 1104 reports from 126 botanical families. A. besseyi, A. fragariae and A. ritzemabosi represent 94% of the reports, circa 83% and 16% of the total reports correspond to flowering plants and ferns, respectively, with three records on conifers and two from other botanical groups also listed. Most plant-parasitic Aphelenchoides show a remarkably broad diversity of associated plants. Most species appear to have no specific plant hosts (i.e. are generalists). The broad host ranges of these species and absence of more intimate interactions with the associated plants highlights the primitive mode of parasitism in Aphelenchoides species, making them potentially interesting in the study of the evolution of plant parasitism. Even though the compiled list of associated plants is long, it probably only represents a fraction of the potential range. The complete compilation has been uploaded to http://nematodes.myspecies.info/.

Calreticulin is required for responding to stress, foraging, and fertility in the white-tip nematode, Aphelenchoides besseyi.

Calreticulin (CRT) regulates a wide array of cellular responses in physiological and pathological processes. A full-length cDNA-encoding CRT protein, namely AbCRT-1, was isolated from Aphelenchoides besseyi, an ectoparasitic plant nematode and the agent of white tip disease of rice. The deduced amino acid sequence of AbCRT-1 was highly homologous with other nematode CRTs, and showed the closest evolutionary relationship with BxCRT-1. In-situ hybridization showed that AbCRT-1 is specifically located in the oesophageal gland and gonads of A. besseyi, suggesting its potential role in parasitism and reproduction. Quantity real-time PCR analysis showed that AbCRT-1 is highly expressed in female nematodes but poorly expressed in eggs, juveniles, and male nematodes. Exposing the nematode to relatively low osmotic stress promotes the transcription of AbCRT-1 whereas extreme desiccation suppresses the transcription significantly. Nematodes in which AbCRT-1 mRNA level had been knocked down by soaking them in AbCRT-1 dsRNA solution distributed randomly and did not aggregate temporally, with a decreased capacity of food discernment. Thus the affected nematodes were markedly less fecund. These results demonstrate that AbCRT-1 is required in A. besseyi for responding to stress, foraging, and fertility.