Cereal Cyst Nematode Research Articles

Resistance to Cereal Cyst Nematodes in Wheat and Barley: An Emphasis on Classical and Modern Approaches.

Cereal cyst nematodes (CCNs) are among the most important nematode pests that limit production of small grain cereals like wheat and barley. These nematodes alone are estimated to reduce production of crops by 10% globally. This necessitates a huge enhancement of nematode resistance in cereal crops against CCNs. Nematode resistance in wheat and barley in combination with higher grain yields has been a preferential research area for cereal nematologists. This usually involved the targeted genetic exploitations through natural means of classical selection breeding of resistant genotypes and finding quantitative trait luci (QTLs) associated with resistance genes. These improvements were based on available genetic diversity among the crop plants. Recently, genome-wide association studies have widely been exploited to associate nematode resistance or susceptibility with particular regions of the genome. Use of biotechnological tools through the application of various transgenic strategies for enhancement of nematode resistance in various crop plants including wheat and barley had also been an important area of research. These modern approaches primarily include the use of gene silencing, exploitation of nematode effector genes, proteinase inhibitors, chemodisruptive peptides and a combination of one or more of these approaches. Furthermore, the perspective genome editing technologies including CRISPR-Cas9 could also be helpful for improving CCN resistance in wheat and barley. The information provided in this review will be helpful to enhance resistance against CCNs and will attract the attention of the scientific community towards this neglected area.

Fine mapping of Rha2 in barley reveals candidate genes for resistance against cereal cyst nematode

Key messageThe cereal cyst nematode resistance locus Rha2 was mapped to a 978 kbp region on the long arm of barley chromosome 2H. Three candidate genes are discussed.The cereal cyst nematode (CCN) Heterodera avenae is a soil-borne obligate parasite that can cause severe damage to cereals. This research involved fine mapping of Rha2, a CCN resistance locus on chromosome 2H of barley. Rha2 was previously mapped relative to restriction fragment length polymorphisms (RFLPs) in two mapping populations. Anchoring of flanking RFLP clone sequences to the barley genome assembly defined an interval of 5077 kbp. Genotyping-by-sequencing of resistant and susceptible materials led to the discovery of potentially useful single nucleotide polymorphisms (SNPs). Assays were designed for these SNPs and applied to mapping populations. This narrowed the region of interest to 3966 kbp. Further fine mapping was pursued by crossing and backcrossing the resistant cultivar Sloop SA to its susceptible ancestor Sloop. Evaluation of F2 progeny confirmed that the resistance segregates as a single dominant gene. Genotyping of 9003 BC2F2 progeny identified recombinants. Evaluation of recombinant BC2F3 progeny narrowed the region of interest to 978 kbp. Two of the SNPs within this region proved to be diagnostic of CCN resistance across a wide range of barley germplasm. Fluorescence-based and gel-based assays were developed for these SNPs for use in marker-assisted selection. Within the candidate region of the reference genome, there are nine high-confidence predicted genes. Three of these, one that encodes RAR1 (a cysteine- and histidine-rich domain-containing protein), one that is predicted to encode an acetylglutamate kinase and one that is predicted to encode a tonoplast intrinsic protein, are discussed as candidate genes for CCN resistance.

Relative susceptibility and tolerance of thirteen Egyptian wheat cultivars to the cereal cyst nematode (Heterodera avenae Woll.)

Relative susceptibility and tolerance of thirteen Egyptian wheat cultivars to the cereal cyst nematode (Heterodera avenae Woll.)

Morphometric and genetic variability among Mediterranean cereal cyst nematode ( Heterodera latipons ) populations in Turkey

The Mediterranean cereal cyst nematode, Heterodera latipons, is an important plant parasitic nematode that negatively impacts cereal production worldwide, particularly in the Mediterranean Basin. Successful control of cereal cyst nematodes requires knowledge of the nematode species/pathotypes and their biology. However, little information is currently available concerning the phenotypic and genotypic variability of H. latipons populations in Turkey. This study analyzed the morphological/morphometric and genetic characteristics of Turkish H. latipons populations to define intraspecific distinctions between them. Morphological and morphometric studies focused on the pattern of the perineal region of cysts and second stage juveniles (J2), while the molecular analyses used sequenced ITS-rDNA regions targeting the internal transcribed spacer (ITS) region of rDNA. The data from these investigations demonstrate that nematode populations from Adana and Hatay provinces differ from the populations collected in Kilis, Gaziantep, and Mardin provinces. These phenotypic and genotypic differences between H. latipons populations may indicate that they are heterogenic, with at least two pathotypes. To date, this study is the most comprehensive analysis identifying H. latipons populations in major wheat-producing areas of Turkey.

The Tryptophan decarboxylase 1 Gene From Aegilops variabilis No.1 Regulate the Resistance Against Cereal Cyst Nematode by Altering the Downstream Secondary Metabolite Contents Rather Than Auxin Synthesis.

Cereal cyst nematode (CCN, Heterodera avenae) is a most important pathogen of wheat and causes tremendous yield loss annually over the world. Since the lack of resistance materials among wheat cultivars, identification and characterization of the resistance-related genes from the relatives of wheat is a necessary and efficient way. As a close relative of wheat with high resistance against CCN, Aegilops variabilis No.1 is believed to be a valuable source for wheat breeding against this devastating disease. However so far, very few resistance-associated genes have been characterized from this species. In this study, we present that the tryptophan decarboxylase genes from Ae. variabilis No.1 (AeVTDC1 and AeVTDC2) were both induced by CCN juveniles at the early stage of resistance response (30 h post-inoculation), with AeVTDC1 more sensitive to CCN infection than AeVTDC2. Silencing of AeVTDC1 led to compromised immunity to CCN with more CCN intrusion into roots; while overexpression AeVTDC1 in Nicotiana tabacum dramatically enhanced the resistance of plants by reducing the knots formed on roots. Metabolism analysis showed that the contents of secondary metabolites with activity of resistance to varied pathogens correlated with the expression level of AeVTDC1 in both Ae. variabilis No.1 and the transgenic tobacco plants. In addition, the content of IAA was not affected by either silencing or overexpressing of AeVTDC1. Hence, our research provided AeVTDC1 a valuable target that mediates resistance to CCN and root knot nematode (RKN, Meloidogyne naasi) without influencing the auxin biosynthesis.

Bio-control potential of Bacillus isolates against cereal cyst nematode (Heterodera avenae)

Bio-control potential of Bacillus isolates against cereal cyst nematode (Heterodera avenae)

Inhabiting plant roots, nematodes, and truffles—Polyphilus, a new helotialean genus with two globally distributed species

ABSTRACTFungal root endophytes, including the common group of dark septate endophytes (DSEs), represent different taxonomic groups and potentially diverse life strategies. In this study, we investigated two unidentified helotialean lineages found previously in a study of DSE fungi of semiarid grasslands, from several other sites, and collected recently from a pezizalean truffle ascoma and eggs of the cereal cyst nematode Heterodera filipjevi. The taxonomic positions and phylogenetic relationships of 21 isolates with different hosts and geographic origins were studied in detail. Four loci, namely, nuc rDNA ITS1-5.8S-ITS2 (internal transcribed spacer [ITS]), partial 28S nuc rDNA (28S), partial 18S nuc rDNA (18S), and partial RNA polymerase II second-largest subunit (RPB2), were amplified and sequenced for molecular phylogenetic analyses. Analyses of similar ITS sequences from public databases revealed two globally distributed lineages detected in several biomes from different geographic regions. The host interaction of isolates from nematodes was examined using in vitro bioassays, which revealed that the fungi could penetrate nematode cysts and colonize eggs of H. filipjevi, confirming observations from field-collected samples. This is the first report of a DSE, and we are not aware of other helotialean fungal species colonizing the eggs of a plant-parasitic nematode. Neither conidiomata and conidia nor ascomata formation was detected in any of the isolates. Based on molecular phylogenetic analyses, these isolates represent a distinct lineage within the Helotiales in the Hyaloscyphaceae. For this lineage, we propose here the new genus Polyphilus represented by two new species, P. sieberi and P. frankenii.

Assessment of yield loss of wheat cultivars caused by Heterodera filipjevi under field conditions

AbstractAmong the cereal cyst nematodes, Heterodera filipjevi is the dominant species of Cereal cyst nematodes (CCNs) in most cereal growing areas of Iran. To evaluate the impact of H. filipjevi on wheat cultivars, a field trial was performed in two infested fields in Isfahan province, Iran 2014 and 2015. The trials were conducted in a factorial experiment based on the complete randomized block design. The treatments consisted of three winter wheat cultivars (Back‐cross Rowshan, Pishtaz and Parsi) which were planted with and without applying nematicide aldicarb Each cultivar was planted in 6 m2 (2 × 3 m) plots which were replicated five times. The nematode reproduction factor was calculated after determining the initial and final population of H. filipjevi in each plot before sowing the seeds and after harvesting. The grain yields and growth parameters were recorded and the variables of 2 years experiment evaluated by linear regression analysis. Cultivar × nematicide treatment combinations in the first and second years showed that H. filipjevi significantly affected grain yield and growth parameters in all three cultivars. The results revealed significant reduction of grain yield by 24.8%, 24.8% and 20.4% in Back‐cross Rowshan, Pishtaz and Parsi cultivars, respectively. The nematode reproduction factor ranged from 0.32 to 1.76 in plots plus and minus nematicide application, respectively. The analysis showed linear inverse relationships between the initial population (Pi) and the yields of wheat cultivars in check plots without aldicarb application.

Host status of Brachypodium distachyon to the cereal cyst nematode

Cereal cyst nematode (Heterodera avenae, CCN) distributes worldwide and has caused severe damage to cereal crops, and a model host will greatly aid in the study of this nematode. In this research, we assessed the sensitivity of 25 inbred lines of Brachypodium distachyon to H. avenae from Beijing, China. All lines of B. distachyon were infested by second-stage juveniles (J2s) of H. avenae from Daxing District of Beijing population, but only 13 inbred lines reproduced 0.2–3 cysts/plant, showing resistance. The entire root system of the infested B. distachyon appeared smaller and the fibrous roots were shorter and less numerous. We found that a dose of 1 000 J2s of H. avenae was sufficient for nematode infestation. We showed that Koz-1 of B. distachyon could reproduce more cysts than TR2A line. Line Koz-1 also supported the complete life cycles of 5 CCN geographical populations belonging to the Ha1 or Ha3 pathotype group. Our results suggest that B. distachyon is a host for CCN.

Investigation of resistance to Pratylenchus penetrans and P. thornei in international wheat lines and its durability when inoculated together with the cereal cyst nematode Heterodera avenae, using qPCR for nematode quantification

The root lesion nematodes Pratylenchus penetrans and P. thornei cause high yield losses in rain-fed wheat fields in Morocco, as well as worldwide. Growing resistant varieties is one of the most effective methods for controlling nematodes. Therefore, a collection of 14 lines of spring wheat and 11 lines of winter wheat (Triticum aestivum and T. durum), provided by CIMMYT, were screened for resistance to P. penetrans and P. thornei in tubes (15 × 20 × 120 mm3) under greenhouse conditions. The resistance level was evaluated based on the numbers of nematodes extracted from roots and soil 9 weeks after infestation. Three lines (L9, L12 and L13) were found moderately resistant (reproduction factor < 1) to P. thornei and one of these (L9) was also moderately resistant to P. penetrans. To investigate the durability of this resistance, we co-inoculated juveniles of Heterodera avenae, a cereal cyst nematode widely present in Moroccan wheat fields, and assessed the reproduction of both lesion nematodes on the three lines. Our results showed that the lines L9, L12, L13 remained moderately resistant in the presence of H. avenae. Moreover, the numbers of Pratylenchus spp. were generally lower when plants were co-inoculated with H. avenae. The number of P. penetrans or P. thornei were determined visually using a microscope and with a qPCR assay. The counts with qPCR were even lower than microscopic counts. These findings on resistance are promising but the field performance of these lines against root lesion nematode attacks should be evaluated.

Genome and secretome analysis of Pochonia chlamydosporia provide new insight into egg-parasitic mechanisms

Pochonia chlamydosporia infects eggs and females of economically important plant-parasitic nematodes. The fungal isolates parasitizing different nematodes are genetically distinct. To understand their intraspecific genetic differentiation, parasitic mechanisms, and adaptive evolution, we assembled seven putative chromosomes of P. chlamydosporia strain 170 isolated from root-knot nematode eggs (~44 Mb, including 7.19% of transposable elements) and compared them with the genome of the strain 123 (~41 Mb) isolated from cereal cyst nematode. We focus on secretomes of the fungus, which play important roles in pathogenicity and fungus-host/environment interactions, and identified 1,750 secreted proteins, with a high proportion of carboxypeptidases, subtilisins, and chitinases. We analyzed the phylogenies of these genes and predicted new pathogenic molecules. By comparative transcriptome analysis, we found that secreted proteins involved in responses to nutrient stress are mainly comprised of proteases and glycoside hydrolases. Moreover, 32 secreted proteins undergoing positive selection and 71 duplicated gene pairs encoding secreted proteins are identified. Two duplicated pairs encoding secreted glycosyl hydrolases (GH30), which may be related to fungal endophytic process and lost in many insect-pathogenic fungi but exist in nematophagous fungi, are putatively acquired from bacteria by horizontal gene transfer. The results help understanding genetic origins and evolution of parasitism-related genes.

First Report of Cyst Nematode (Heterodera iri) in Ohio

HomePlant DiseaseVol. 102, No. 5First Report of Cyst Nematode (Heterodera iri) in Ohio PreviousNext DISEASE NOTES OPENOpen Access licenseFirst Report of Cyst Nematode (Heterodera iri) in OhioS. Joseph, F. Akyazi, A. Habtewld, T. Mekete, T. Creswell, G. E. Ruhl, and J. FaghihiS. JosephSearch for more papers by this author, F. AkyaziSearch for more papers by this author, A. HabtewldSearch for more papers by this author, T. MeketeSearch for more papers by this author, T. Creswell†Corresponding author: T. Creswell; E-mail: E-mail Address: creswell@purdue.eduSearch for more papers by this author, G. E. RuhlSearch for more papers by this author, and J. FaghihiSearch for more papers by this authorAffiliationsAuthors and Affiliations S. Joseph F. Akyazi A. Habtewld T. Mekete , Entomology and Nematology Department, University of Florida, Gainesville, 32611 T. Creswell † G. E. Ruhl , Plant and Pest Diagnostic Laboratory, Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN 47907 J. Faghihi , Department of Entomology, Purdue University, West Lafayette, IN 47907. Published Online:23 Mar 2018https://doi.org/10.1094/PDIS-11-17-1846-PDNAboutSectionsSupplemental ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmailWechat The cyst nematodes (Heterodera spp.) are a major group of plant-parasitic nematodes and of great economic importance in many countries throughout the world, causing considerable yield losses to many important crops (Jones et al. 2013). The cereal cyst nematodes (CCNs) are a widespread and important group of cyst nematodes that restrict production of cereal crops throughout the world (Rivoal and Cook 1993). The CCNs that belong to the Heterodera avenae complex infect roots of cereals and grasses (Handoo 2002). Four species from this group have been reported in the United States, including H. avenae, H. filipjevi, H. mani, and H. ustinovi (syn. H. iri). H. iri has previously been reported only in New York, Michigan, Connecticut, Massachusetts, and Rhode Island (LaMondia and Wick 1992). Cyst nematodes were identified from an Ohio bentgrass golf course sample submitted to the Purdue Plant and Pest Diagnostic Lab and the Purdue Nematology Lab for diagnosis in 2016. The affected turf had irregular patches of thinning, translucent leaves, and reduced root systems. Cysts were collected from the infested soil by the modified Jenkins sugar flotation method (Jenkins 1964) and identified by morphological and molecular study. Morphometrics (mean ± SD) of second-stage juveniles (n = 12): body length = 661.7 ± 23.8 µm; a = 29.6 ± 1.3 µm; c = 7.3 ± 0.3 µm; c′ = 5.2 ± 0.5 µm; stylet length = 27.3 ± 0.5 µm; maximum body width = 22.4 ± 0.4 µm; body width at anus = 17.5 ± 2.1 µm; tail length = 90.9 ± 5.1 µm; hyaline tail length = 55.4 ± 4.8 µm; and hyaline tail /stylet length = 2.1 ± 0.2 µm. Morphometrics of cysts (n = 10): length (without neck) = 654.4 ± 82.9 µm; width = 461.8 ± 84.2 µm; neck length = 127.4 ± 20.8 µm; length/width = 1.4 ± 0.2. The vulval cone was bifenestrate with a strong vulval bridge and conspicuous bullae. Morphometrics of vulval cone (n = 7): fenestral length = 42.4 ± 4.1 µm; fenestral width = 24.4 ± 2.1 µm; vulval slit = 12.9 ± 1.4 µm; and vulval bridge = 3.1 ± 0.5 µm. Eggs (n = 10) measured length = 136.5 ± 8.9 µm; width = 43.7 ± 2.8 µm; and length/width = 3.1 ± 0.3. These morphological measurements were highly similar with those for H. iri as described by Mathews (1971). Genomic DNA was extracted from five nematodes. The ribosomal region spanning the internal transcribed spacer (ITS) 1, 5.8S gene, and ITS2 was amplified with forward primers AB28F (5′-GTTTCCGTAGGTGAACCTGC-3′) and reverse primer TW81R (5′-ATATGCTTAAGTTCAGCGGGT-3′). A 973-bp fragment was amplified, and the polymerase chain reaction product was purified and sequenced. The sequence was deposited in GenBank (accession no. KX611142). BLAST search results revealed a sequence similarity of 99% with H. iri (e.g., GenBank accession nos. AY148407.1 and AF274400.1) over 100% query cover. Morphological and molecular identification demonstrated that the population of cyst nematodes from Ohio was H. iri. Reproduction on bentgrass was demonstrated by inoculating 1,000 viable eggs onto 5-week-old bentgrass seedlings grown in 4-in. pots (n = 2) of sterilized sand at 23°C. A pot of noninoculated seedlings served as a control. Sixty days after inoculation, cysts were harvested from the plants, and extraction produced approximately 2,000 eggs, demonstrating multiplication on this host. No cysts were found on the control plants. To our knowledge, this detection represents a new record of H. iri in Ohio.

Genetic variation of bread wheat accessions in response to the cereal cyst nematode, Heterodera filipjevi

SummaryBread wheat,Triticum aestivum, produces large edible grains and is consumed by 75% of the world’s populations. Cereal cyst nematodes have a global distribution and cause significant economic yield losses in many countries. Therefore, there is an urgent need to identify new resistance sources. In this study, the genetic diversity of 43 wheat accessions in response to cereal cyst nematode,Heterodera filipjeviIsfahan pathotype, was assessed using a simple sequence repeat (SSR) marker. Seven primers were used, out of which five primers showed polymorphisms. Alleles per primer varied from one to three per locus (mean 2.85). The highest and lowest polymorphic information content of 0.81 and 0.44 (mean 0.66) were related to Xgwm 3012DL and Xgwm147, respectively. Genetic similarity was 29-88% between accessions. SSR analysis divided the accessions into five main groups. Resistant cultivars ‘Bam’ and ‘Behrang’ possessed bothCre1 andCre8 resistant genes. TheCre3 andCatgenes were partially sequenced in five cultivars of different responses toH. filipjevi. The nucleotide sequences were compared toCre3 andCathomologues, indicating 93-100% and 86-92% homology, respectively. The MEGA program showed highest similarity ofCre3 andCatgenes amplified with the resistance gene analogues (RGA14) in the wheat andCat3-A1 gene in ‘Carnamah’. This research showed that SRR markers could efficiently verify genetic diversity between wheat accessions, and the known resistance genes (Cregenes) against the cereal cyst nematodes could not control theH. filipjeviIsfahan pathotype populations, except theCre1 gene.

Amino acid permease 6 modulates host response to cyst nematodes in wheat and Arabidopsis

Summary Cyst nematodes are plant parasites that cause significant crop loss in wheat and other crops. Infective juveniles invade roots and induce syncytial feeding structures as the only source of nutrients throughout their life. A previous genome-wide association study in wheat identified amino acid permease 6 (TaAAP6) to be linked to susceptibility to the cereal cyst nematode Heterodera filipjevi. To characterise the role of AAP6 during nematode parasitism, we analysed the expression of TaAAP6 and the Arabidopsis orthologue AtAAP6. TaAAP6 was found to be highly expressed in nematode-infected roots of susceptible wheat, whereas it was not upregulated in nematode-infected roots of resistant accessions. AtAAP6 was also found to be highly upregulated in nematode-induced syncytia compared with non-infected roots. Infection assays with an AtAAP6 knock-out mutant revealed reduction in developing females, female size, and size of female-associated syncytia, thus indicating the importance of AAP6 in cyst nematode parasitism.

Incidence and geographical distribution of cereal cyst nematode (CCN, Heterodera spp.) in winter wheat fields in Algeria

espanolLos nematodos enquistados de los cereales (CCN, Heterodera spp.) son los nematodos parasitos vegetales mas daninos para el trigo, especialmente en las zonas de cultivo de cereales, en todo el mundo. En el verano de 2015 tomamos muestras en 22 trigales y las analizamos utilizando la tecnica del embudo de Fenwick. El estudio revelo que el 54,55% de los trigales estaban infestados por nematodo enquistado de los cereales. La infestacion se observo en varias localizaciones del norte de Argelia, pero no en la zona desertica del sur. Las densidades de poblacion de CCN en el suelo de las zonas infestadas variaron entre 0,6 ± 0,54 y 8,6 ± 19,96 quistes/500 g de suelo seco. Ademas, hallamos un promedio de 56,33 ± 15,18 y 364,70 ± 81,93 segundos estadios juveniles y huevos por quiste, respectivamente. La infestacion era mas severa en los campos dedicados al cereal de Draa Semar y Djendel, con 86,6 ± 19,96 quistes/500 g de suelo y 57,4 ± 17,55 quistes/500 g de suelo, respectivamente. Las tasas mas bajas de infestacion se observaron en los otros campos: Ras Elouad, Sidi Mbarek y Sedraia, con 0,6 ± 0,54 quistes/500 g de suelo, 1,6 ± 1,67 quistes/500 g de suelo y 2,4 ± 1,67 quistes/500 g de suelo, respectivamente. Heterodera spp. estaba distribuido en toda la zona de cultivo de cereal de Argelia y podria causar una perdida de rendimiento economico en esas regiones. Mostramos la distribucion en un mapa. EnglishCereal cyst nematodes (CCN, Heterodera spp.) are the most damaging plant-parasitic nematode species on wheat, causing severe economic loss in global wheat production. In summer 2015, we analyzed samples collected from 22 wheat fields in Algeria using the Fenwick can technique. The study revealed that 54.55 % of wheat fields were infested with cereal cyst nematodes. The species was observed in several locations in the northern part of Algeria but not in the southern desert area. Population densities of CCNs in soil varied between the regions at an infestation rate of between 0.6 ± 0.54 and 86.6 ± 19.96 cysts per 500 g of dried soil. Furthermore, we found an average of 56.33±15.18 and 364.70 ± 81.93 second-stage juveniles and eggs/cyst. The infestation was most severe in cereal fields in Draa Semar and Djendel with 86.6 ± 19.96 cyst/500g of soil and 57.4±17.55 cysts/500g of soil, respectively. Infestation was lowest in fields in Ras Elouad, Sidi Mbarek and Sedraia with 0.6 ± 0.54 cysts/500g of soil; 1.6 ± 1.67 cysts/500g of soil and 2.4 ± 1.67 cysts/500g of soil, respectively. Heterodera spp. was distributed throughout the cereal growing province in Algeria and could cause economic loss in these regions. catalaEls nematodes enquistats dels cereals (CCN, Heterodera spp.) son els nematodes parasits vegetals mes nocius per al blat, especialment a les zones de conreu de cereals, arreu del mon. L’estiu de 2015 vam prendre mostres en 22 camps de blat i les vam analitzar mitjancant la tecnica de l’embut de Fenwick. L’estudi va revelar que el 54,55 % dels camps de blat estaven infestats pel nematode enquistat dels cereals. La infestacio es va observar en diverses localitzacions del nord d’Algeria, pero no a la zona desertica del sud. Les densitats de poblacio de CCN al sol de les zones infestades van variar entre 0,6 ± 0,54 i 8,6 ± 19,96 quists/500 g de sol sec. A mes, vam trobar una mitjana de 56,33 ± 15,18 i 364,70 ± 81,93 segons estadis juvenils i ous per quist, respectivament. La infestacio era mes severa als camps dedicats al cereal de Draa Semar i Djendel, amb 86,6 ± 19,96 quists/500 g de sol i 57,4 ± 17,55 quists/500 g de sol, respectivament. Les taxes mes baixes d’infestacio es van observar als altres camps: Ras Elouad, Sidi Mbarek i Sedraia, amb 0,6 ± 0,54 quists/500 g de sol, 1,6 ± 1,67 quists/500 g de sol i 2,4 ± 1,67 quists/500 g de sol, respectivament. Heterodera spp. estava distribuit en tota la zona de conreu de cereal d’Algeria i podria causar una perdua de rendiment economic en aquestes regions. En mostrem la distribucio en un mapa.

DNA barcoding, phylogeny and phylogeography of the cyst nematode species of the Avenae group from the genus Heterodera (Tylenchida: Heteroderidae)

Summary Among the recognised species groups of Heterodera, the Avenae group is one of the largest with a total of 12 species. Ten of them, H. arenaria, H. aucklandica, H. australis, H. avenae, H. filipjevi, H. mani, H. pratensis, H. riparia, H. sturhani and H. ustinovi, are morphologically closely related and represent the H. avenae species complex, and the other two, H. hordecalis and H. latipons, are morphologically more distinct from this complex. In this study we provide comprehensive phylogenetic analyses of several hundred COI and ITS rRNA gene sequences from the Avenae group using Bayesian inference, maximum likelihood and statistical parsimony. Some 220 COI and 11 ITS rRNA new gene sequences from 147 nematode populations collected in 26 countries were obtained in this study. Our study showed that the COI gene is a powerful DNA barcoding marker for identification of populations and species from the Avenae group. A putatively new cyst nematode species related to H. latipons was revealed from the analysis of COI and ITS rRNA gene datasets. COI gene sequences allow distinguishing H. arenaria, H. australis and H. sturhani from each other and other species. Problems of species delimiting of these species are discussed. The results of the analysis showed that COI haplotypes corresponded to certain pathotypes of the cereal cyst nematodes. It is recommended that information on COI haplotypes of studied populations be included in research with these nematodes. Based on the results of phylogeographical analysis and age estimation of clades with a molecular clock approach, it was hypothesised that several species of the Avenae group primarily originated and diversified in the Irano-Anatolian hotspot during the Pleistocene and Holocene periods and then dispersed from this region across the world. Different geographic barriers, centres and times of origin might explain current known distribution patterns for species of the Avenae group. Possible pathways, including a long distance trans-Atlantic dispersal, and secondary centres of diversification are proposed and discussed.

First Report of Cereal Cyst Nematode (Heterodera filipjevi) on Winter Wheat in Xinjiang Uygur Autonomous Region, China

The cereal cyst nematode Heterodera filipjevi is considered to be one of the most important plant parasitic nematodes attacking most cereals and can cause significant crop losses (Sikora 1988). In China, this nematode was first recorded in Henan province in 2009 and a few years later in Anhui province (Peng et al. 2016). During May 2015 to August 2016, a survey for important plant parasitic nematodes on wheat and sugar beet was undertaken in Xinjiang Uygur Autonomous Region of China; 50 soil samples were collected, and the weight of each sample was about 1 kg. The cysts and second-stage juveniles (J2) were extracted from each soil sample using the sieving-decanting method. Morphological and molecular studies (Subbotin et al. 2010) of cysts and J2 confirmed the identification of H. filipjevi in two wheat-field soil samples from Xinyuan county of Yining city. There were no significant above-ground symptoms on wheat, but a few females were found on roots. The cysts were lemon shaped with light to dark brown cyst walls. Subcrystalline layer thick, valval core ambifenestrate, bullae large and numerous, and underbridge observed. The key morphometrics of cysts (n = 10) were length excluding neck (range = 705 to 887 μm, mean = 775 µm, standard deviation = 30.5); width (478 to 694, 571, 15), fenestra length (45.2 to 63.9, 54.7, 2.1), fenestra width (26.9 to 34.8, 28.4, 1.2), length of vulval slit (7.5 to 12.5, 9.4, 0.5), and length of underbridge (71.4 to 84.5, 76.4, 4.8). Measurements of J2s (n = 20) included length of body (range = 481.1 to 581.5 μm, mean = 540 µm, standard deviation = 7.1), stylet (24.5 to 27, 24.7, 0.2), tail (53.4 to 65.3, 61.2, 1.4), and hyaline tail terminus (30.4 to 42.2, 36.5, 0.7). Genomic DNA was isolated from single cysts (n = 5), and the internal transcribed spacer regions were amplified with primers TW81 (5′-GTTTCCGTAGGTGAACCTGC-3′) and AB28 (5′-ATATGCTTAAGTTCAGCGGGT-3′) (De Ley et al. 1999). The obtained sequences (GenBank accession nos. KY448472 and KY448473, 1,054 bp) were found to be 99 to 100% identical to those of H. filipjevi from the United States (KP878490.1 and GU079654.1), Turkey (KR704304.1 and KR704308.1), and China (KT314234.1 and GU083595.1). The species-specific primers were used and produced a single band specific for H. filipjevi (Peng et al. 2013). Pathogenicity of the H. filipjevi was confirmed by infection of wheat and examination of the nematode development and reproduction. Wheat (Triticum aestivum ‘Wenmai 19’), was cultured in 300 cm³ pots filled with autoclaved soil in a glasshouse, and 800 eggs were inoculated into the soil near the roots of 4-day-old seedlings. The parasitic J2s, third and fourth-stage juveniles, and adult females were observed in roots stained with acid fuchsin at 7, 14, 28, and 35 days after inoculation (DAI), and an average of 51 cysts per pot were extracted 50 DAI. The new cysts’ morphological and molecular characteristics were identical to the H. filipjevi cysts from the original soil samples. To our knowledge, this is the first report of H. filipjevi in Xinjiang Uygur Autonomous Region, China. If this nematode continues to spread in China, it could become be a new threat to cereal production, so some effective control should be taken to prevent further spread.

Transcriptional responses of wheat and the cereal cyst nematode Heterodera avenae during their early contact stage

Cereal cyst nematode (Heterodera avenae) is attracted to and aggregated around wheat roots to initiate infection, but this interaction between wheat and the nematode is not fully understood. The transcriptional responses of both wheat and H. avenae were examined during their early contact stage by mRNA sequencing analysis; certain numbers of the differentially expressed genes (DEGs) were validated using quantitative real-time PCR. The immobile host wheat root only had 93 DEGs (27 up-regulated and 66 down-regulated), while the mobile plant parasitic nematode reacted much more actively with 879 DEGs (867 up-regulated and 12 down-regulated). Among them, a number of wheat DEGs (mostly down-regulated) were involved in biotic stress pathways, while several putative effector genes were up-regulated in the nematode DEGs. One putative chitinase-like effector gene of H. avenae was able to suppress BAX-triggered programmed cell death in Nicotiana benthamiana. Results of these experiments demonstrated that nematode responded more actively than wheat during the contact stage of parasitism. The parasite’s responses mainly involved up-regulation of genes including at least one anti-plant-defence effector gene, whereas the host responses mainly involved down-regulation of certain defence-related genes.

Phenotype and Cellular Response of Wheat Lines Carrying Cre Genes to Heterodera avenae Pathotype Ha91.

The cereal cyst nematode (CCN, Heterodera avenae), a major limiting factor for wheat production worldwide, is widespread in most wheat-growing regions in China. Accordingly, screening and characterization of resistant (R) wheat sources against H. avenae are very important. In this study, we screened 51 wheat lines, collected from the International Wheat and Maize Improvement Center (CIMMYT), carrying various Cre genes (Cre1, Cre2, Cre3, Cre5, Cre7, Cre8, CreR, and Pt). From that screen, we identified one immune (M) cultivar (with no adult females produced) and five resistant cultivars (with fewer than five females) to H. avenae pathotype Ha91. The Cre3 gene conferred the most effective resistance against H. avenae pathotype Ha91 in both field and greenhouse assays. Conversely, the Cre1 and CreR genes conferred the poorest effective resistance. Using Pluronic F-127 gel and a staining assay, juvenile nematodes invading wheat roots were observed, and nematode development was analyzed. Compared with R and M roots, those of the susceptible (S) wheat cultivar Wenmai19 were more attractive to H. avenae second-stage juveniles (J2s). We observed the retardation of nematode development in R cultivars and tiny white female cysts protruding from the R cultivar VP1620. Nematodes in M roots either disintegrated or remained J2s or third-stage juveniles (J3s) and failed to complete their life cycle. Molting was also suppressed or delayed in R and M genotypes. For both S and R cultivars, syncytia were characterized by cell wall perforations and dense cytoplasm in hypertrophied syncytium component cells. Syncytial size increased gradually with nematode development in S cultivars. Moreover, an incompatibility reaction occurred in M wheat roots: the syncytium was disorganized, exhibiting disintegration and condensed nuclei. These sources of genetic resistance against CCN can potentially be planted in severely infested fields to reduce economic loss or can be used for introgression in breeding.

Characterization of cereal cyst nematodes (Heterodera spp.) in Morocco based on morphology, morphometrics and rDNA-ITS sequence analysis

AbstractMorphological and molecular diversity among 11 populations of cereal cyst nematodes from different wheat production areas in Morocco was investigated using light microscopy, species-specific primers, complemented by the ITS-rDNA sequences. Morphometrics of cysts and second-stage juveniles (J2s) were generally within the expected ranges forHeterodera avenae; only the isolate from Aïn Jmaa showed morphometrics conforming to those ofH. latipons. When using species-specific primers forH. avenaeandH. latipons, the specific bands of 109 bp and 204 bp, respectively, confirmed the morphological identification. In addition, the internal transcribed spacer (ITS) regions were sequenced to study the diversity of the 11 populations. These sequences were compared with those ofHeteroderaspecies available in the GenBank database (www.ncbi.nlm.nih.gov) and confirmed again the identity of the species. Ten sequences of the ITS-rDNA were similar (99–100%) to the sequences ofH. avenaepublished in GenBank and three sequences, corresponding with one population, were similar (97–99%) toH. latipons.