A Quantitative Trait Locus with a Major Effect on Root-Lesion Nematode Resistance in Barley.

Although the root-lesion nematode Pratylenchus thornei is known to affect barley (Hordeum vulgare L.), there have been no reports on the genetic control of P. thornei resistance in barley. In this research, P. thornei resistance was assessed for a panel of 46 barley mapping parents and for two mapping populations (Arapiles/Franklin and Denar/Baudin). With both populations, a highly significant quantitative trait locus (QTL) was mapped at the same position on the long arm of chromosome 7H. Single-nucleotide polymorphisms (SNPs) in this region were anchored to an RGT Planet pan-genome assembly and assayed on the mapping parents and other barley varieties. The results indicate that Arapiles, Denar, RGT Planet and several other varieties likely have the same resistance gene on chromosome 7H. Marker assays reported here could be used to select for P. thornei resistance in barley breeding. Analysis of existing barley pan-genomic and pan-transcriptomic data provided a list of candidate genes along with information on the expression and differential expression of some of those genes in barley root tissue. Further research is required to identify a specific barley gene that affects root-lesion nematode resistance.

The Root-Lesion Nematode, Pratylenchus penetrans, Affects Early Growth and Physiology of Grafted M.9, G.41, and G.935 Apple Rootstocks Similarly Under Field Microplot Conditions.

The root-lesion nematode, Pratylenchus penetrans, is a ubiquitous parasite of roots of temperate fruit trees. It affects early growth of trees replanted into former orchard sites where populations have built up and may contribute to decline complexes of older trees. Most British Columbia, Canada, apple acreage is planted with M.9 rootstock, but growers are increasingly considering Geneva-series rootstocks such as G.41 and G.935. Among these rootstocks, responses to P. penetrans, specifically, are poorly known. To compare the resistance and tolerance to P. penetrans of G.41, G.935, and M.9 rootstocks ('Ambrosia' scion), a field microplot experiment was established in spring of 2020 at the Summerland Research and Development Centre. The experimental design was a two by three factorial combination of: P. penetrans inoculation (+/-) and rootstock (G.41, G.935, and M.9), with 20 replicate microplots of each of the six treatment combinations arranged in a randomized complete block design. The P. penetrans inoculum was 5,400 nematodes per microplot (54 P. penetrans liter-1 soil), which is below commonly accepted damage thresholds. Though P. penetrans population densities were lower for the G.41 rootstock by the end of the 2021 growing season, the effects of P. penetrans were similar among rootstocks. In the establishment year (2020), P. penetrans caused significant reductions in aboveground growth. In 2021, shoot growth and root weight were reduced by P. penetrans. The nematode also reduced rates of leaf gas exchange and stem water potential. These data suggest that while G.41 and G.935 may have other horticultural benefits over M.9, they are equally susceptible to P. penetrans at the early stages of tree growth.

Host response of Nicotiana benthamiana to the parasitism of five populations of root-lesion nematode, Pratylenchus coffeae, from China.

In a recent survey of nematodes associated with tobacco in Shandong, China, the root-lesion nematode Pratylenchus coffeae was identified using a combination of morphology and molecular techniques. This nematode species is a serious parasite that damages a variety of plant species. The model plant benthi, Nicotiana benthamiana, is frequently used to study plant-disease interactions. However, it is not known whether this plant species is a host of P. coffeae. The objectives of this study were to evaluate the parasitism and pathogenicity of five populations of the root-lesion nematode P. coffeae on N. benthamiana.N. benthamiana seedlings with the same growth status were chosen and inoculated with 1,000 nematodes per pot. At 60 days after inoculation, the reproductive factors (Rf = final population densities (Pf)/initial population densities (Pi)) for P. coffeae in the rhizosphere of N. benthamiana were all more than 1, suggesting that N. benthamiana was a good host plant for P. coffeae.Nicotiana. benthamiana infected by P. coffeae showed weak growth, decreased tillering, high root reduction, and noticeable brown spots on the roots. Thus, we determined that the model plant N. benthamiana can be used to study plant-P. coffeae interactions.

Evaluation of Wheat Cultivars and Germplasm Lines for Resistance to Pratylenchus neglectus Populations Collected in North Dakota.

Root-lesion nematode (RLN; Pratylenchus neglectus) is a migratory endoparasite and a major soilborne pathogen that affects wheat (Triticum spp.) production worldwide. Genetic resistance is one of the most economical and effective ways to manage P. neglectus in wheat. This study evaluated 37 local cultivars and germplasm lines in seven greenhouse experiments, including 26 hexaploid wheat, six durum wheat, two synthetic hexaploid wheat, one emmer wheat, and two triticale for P. neglectus resistance from 2016 to 2020. North Dakota field soils infested with two RLN populations (350 to 1,125 nematodes per kilogram of soil) were used for resistance screening under controlled greenhouse conditions. The final nematode population density for each cultivar and line was counted under the microscope to categorize the resistance ranking of these entries as resistant, moderately resistant, moderately susceptible, and susceptible. Out of the 37 cultivars and lines, one was classified as resistant (Brennan); 18 were moderately resistant (Divide, Carpio, Prosper, Advance, Alkabo, SY Soren, Barlow, Bolles, Select, Faller, Briggs, WB Mayville, SY Ingmar, W7984, PI 626573, Ben, Grandin, and Villax St. Jose); 11 were moderately susceptible; and seven were susceptible to P. neglectus. The resistant to moderately resistant lines identified in this study could be used in breeding programs after the resistance genes or loci are further elucidated. This research provides valuable information about P. neglectus resistance among wheat and triticale cultivars used in the Upper Midwest region of the United States.

First Draft Genome Assembly of Root-Lesion Nematode Pratylenchus scribneri Generated Using Long-Read Sequencing.

Root-lesion nematodes (genus Pratylenchus) belong to a diverse group of plant-parasitic nematodes (PPN) with a worldwide distribution. Despite being an economically important PPN group of more than 100 species, genome information related to Pratylenchus genus is scarcely available. Here, we report the draft genome assembly of Pratylenchus scribneri generated on the PacBio Sequel IIe System using the ultra-low DNA input HiFi sequencing workflow. The final assembly created using 500 nematodes consisted of 276 decontaminated contigs, with an average contig N50 of 1.72 Mb and an assembled draft genome size of 227.24 Mb consisting of 51,146 predicted protein sequences. The benchmarking universal single-copy ortholog (BUSCO) analysis with 3131 nematode BUSCO groups indicated that 65.4% of the BUSCOs were complete, whereas 24.0%, 41.4%, and 1.8% were single-copy, duplicated, and fragmented, respectively, and 32.8% were missing. The outputs from GenomeScope2 and Smudgeplots converged towards a diploid genome for P. scribneri. The data provided here will facilitate future studies on host plant-nematode interactions and crop protection at the molecular level.

Multi-locus genome-wide association study of chickpea reference set identifies genetic determinants of Pratylenchus thornei resistance.

Pratylenchus thornei is an economically important species of root-lesion nematode adversely affecting chickpea (Cicer arietinum) yields globally. Integration of resistant crops in farming systems is recognised as the most effective and sustainable management strategy for plant-parasitic nematodes. However, breeding for P. thornei resistance in chickpea is limited by the lack of genetic diversity. We deployed a genome-wide association approach to identify genomic regions and candidate genes associated with P. thornei resistance in 285 genetically diverse chickpea accessions. Chickpea accessions were phenotyped for P. thornei resistance in replicated glasshouse experiments performed for two years (2018 and 2020). Whole genome sequencing data comprising 492,849 SNPs were used to implement six multi-locus GWAS models. Fourteen chickpea genotypes were found to be resistant to P. thornei. Of the six multi-locus GWAS methods deployed, FASTmrMLM was found to be the best performing model. In all, 24 significant quantitative trait nucleotides (QTNs) were identified, of which 13 QTNs were associated with lower nematode population density and 11 QTNs with higher nematode population density. These QTNs were distributed across all of the chickpea chromosomes, except chromosome 8. We identified, receptor-linked kinases (RLKs) on chromosomes 1, 4 and 6, GDSL-like Lipase/Acylhydrolase on chromosome 3, Aspartic proteinase-like and Thaumatin-like protein on chromosome 4, AT-hook DNA-binding and HSPRO2 on chromosome 6 as candidate genes for P. thornei resistance in the chickpea reference set. New sources of P. thornei resistant genotypes were identified that can be harnessed into breeding programs and putative candidate P. thornei resistant genes were identified that can be explored further to develop molecular markers and accelerate the incorporation of improved P. thornei resistance into elite chickpea cultivars.

Host Suitability of Cover Crops to the Root-Lesion Nematode Pratylenchus penetrans Associated with Potato.

Nonhost or poor host cover crops can provide an alternative method for nematode management. A total of 25 cover crop species/cultivars, along with three controls were evaluated in greenhouse experiments for their host suitability to the root-lesion nematode Pratylenchus penetrans. Trials were conducted in a completely randomized design using nematode-infested soil and terminated 3 months after planting. Nematodes were extracted from the roots and soil of each crop to determine their final population densities, reproductive factor (Rf = final population density/initial population density), and distributions in the soil and root habitats. Reproductive factor was used to categorize the host suitability of crops. Faba bean cv. Petite produced the greatest nematode population density in all trials, whereas only alfalfa cv. Bullseye constantly demonstrated the poor host ability to P. penetrans. Annual ryegrass, winter rye cv. ND Dylan, and white proso millet also showed poor hosts in most trials. Five cover crops consistently maintained the population throughout the experiments, with Rf values less than 2, and the remaining tested cover crops were suitable hosts for P. penetrans. The majority of the tested cover crops had less than or equal to 30% of the final population residing in the roots after three months of growth in all the trials. This research helps us gain the knowledge on cover crops and P. penetrans interaction and will be useful for potato growers to select better cover crops and avoid susceptible hosts to manage P. penetrans in infested fields to minimize potato yield losses.

Eco-Friendly Silver Nanoparticles Synthesized from a Soybean By-Product with Nematicidal Efficacy against Pratylenchus brachyurus.

This study explores an eco-friendly approach to synthesizing silver nanoparticles (AgNPs) using soybean leaf extracts, employing a reaction with silver nitrate at 65 °C for 2.5 h. Optimal results were achieved at extract concentrations of 3.12 and 6.25 mg of the leaf mL-1, termed 3.12AgNP and 6.25AgNP, respectively. UV-Vis spectrophotometric analysis between 350 and 550 nm exhibited a peak at 410-430 nm, along with a color transition in the suspensions from pale yellow to brown, indicating successful synthesis. Dynamic light scattering (DLS) further delineated the favorable properties of these AgNPs, including nanometric dimensions (73-104 nm), negative charge, and moderate polydispersity, portraying stable and reproducible synthesis reactions. The bioreduction mechanism, possibly expedited by leaf extract constituents such as amino acids, phenolic acids, and polysaccharides, remains to be fully elucidated. Notably, this study underscored the potent nematicidal effectiveness of biosynthesized AgNPs, especially 6.25AgNP, against Pratylenchus brachyurus, which is a common plant-parasitic nematode in tropical soybean cultivation regions. In vitro tests illustrated significant nematicidal activity at concentrations above 25 µmol L-1, while in vivo experiments displayed a pronounced nematode population diminishment in plant roots, particularly with a 6.25AgNP rhizosphere application at concentrations of 500 µmol L-1 or twice at 250 µmol L-1, attaining a reproduction factor below 1 without any morphological nematode alterations. This research highlights the potential of 6.25AgNPs derived from soybean leaf extracts in forging sustainable nematicidal solutions, marking a significant stride toward eco-friendly phytonematode management in soybean cultivation. This novel methodology signals a promising avenue in harnessing botanical resources for nematode control and propelling a greener agricultural horizon.

First report of Pratylenchus penetrans (Nematoda: Pratylenchidae) associated with artichokes in Vietnam.

Pratylenchus penetrans is one of the world's most common and destructive root-lesion nematodes and can parasitize more than 400 plant species. P. penetrans has been reported to cause serious damage to artichokes in several countries, such as Greece, Brazil, and France. Until now, there have been no reports of P. penetrans associated with artichokes in Vietnam. In this study, we recorded this species in artichoke fields in Lam Dong province, Vietnam with an average density of 50 nematodes/100g of soil (frequency of appearance at 64.7%). This nematode was associated with symptoms such as yellowing leaves, stunt, and root necrosis of artichokes in Vietnam, indicating its high damaging potential and a need for suitable control strategies. The identification of this species in our study was confirmed by morphology, morphometric data, and molecular characterization of 18S and 28S rRNA regions. Our study also provides the first molecular data of P. penetrans in Vietnam. The inclusion of molecular data for P. penetrans in Vietnam represents a significant contribution to the scientific community and a pivotal advancement in addressing nematode-related challenges in agriculture. This dataset serves as an invaluable reference for various molecular-focused endeavors, including but not limited to molecular identification, pathogenicity studies, and the development of effective management strategies.

Impact of Pratylenchus penetrans on Soybean Grown in Wisconsin, U.S.A.

Models were developed to quantify the impact of Pratylenchus penetrans to the early season growth and yield of soybean in field and greenhouse environments and to estimate yield loss because of P. penetrans in Wisconsin. There was a negative linear relationship between initial nematode population densities (Pi) and shoot and total plant weight at V2 and yield, pod number, seed number, and seed mass at harvest in the field. Relative yield loss, modeled for the second year of the field experiment, suggested a loss of 4.5% for yield and between 2.4 and 2.8% for yield components at the mean field Pi value. Negative linear relationships were demonstrated for the relative loss in those variables as well as for harvest index and shoot, root, and total plant weight at harvest in the greenhouse. Stress imposed by P. penetrans began within 2 weeks after planting and continued through harvest. Estimates of the percent loss attributed to each nematode Pi value were 0.020% for yield, 0.015% for pod number, and 0.017% for seed number. Pratylenchus spp. was the most widely prevalent pest nematode among samples submitted to a statewide nematode testing program. Molecular identification of a subset of 63 samples suggested 15% were infested with P. penetrans at a mean Pi value of 197 P. penetrans per 100 cm3 soil. Yield loss because of P. penetrans, estimated from prevalence data and our empirical greenhouse model, ranged from 0.23 to 2.76% among Wisconsin's agricultural districts. The cumulative impact for all Pratylenchus spp. is likely much greater, given this loss estimate does not account for the monoecious species present in 79% of the samples.

Population Development of the Root-Lesion Nematode Pratylenchus dakotaensis on Soybean Cultivars.

Two greenhouse experiments were conducted with the new species of root-lesion nematode, Pratylenchus dakotaensis, discovered in North Dakota, USA in 2017 and named in 2021. Experiment 1 was conducted to ascertain resistance levels of soybean (Glycine max [L.] Merr.) cultivars to the new species P. dakotaensis and Experiment 2 was conducted to evaluate the population levels of P. dakotaensis in roots versus soil. A total of 20 soybean cultivars, and the positive control, cultivar Barnes, accompanying a nonplanted control, were evaluated in both experiments; they each had five replicates and the experiments were repeated. Among the 20 soybean cultivars evaluated, a cultivar with the ID# 13 consistently produced the greatest population densities of P. dakotaensis across all the experiments and therefore it was selected as the susceptible check. The ratio of the final nematode population density of a test cultivar relative to the final population density of the susceptible check was used to scale resistance rating. Combined results of all the trials indicated that seven of the cultivars were moderately resistant, nine of the cultivars plus 'Barnes' were moderately susceptible, and four of the cultivars were susceptible. However, none of the cultivars tested were classified as resistant. Analysis of P. dakotaensis population levels revealed that ≥50% of the population resided in the root habitat and the remaining nematodes were recovered from soil at 9 weeks after planting for a majority of the cultivars tested. These results provide an insight into the virulence of P. dakotaensis on commercial soybean cultivars.

Pratylenchus smoliki, a new nematode species (Pratylenchidae: Tylenchomorpha) from the Great Plains region of North America.

Pratylenchus smoliki is a new species of root-lesion nematode described from corn-soybean production fields in the Central Great Plains of North America. It is characterized by populations with relatively abundant males, two lip annuli, females with a round functional spermatheca and a conoid to subcylindrical tail with a non-crenate, smooth terminus. In host preference tests, corn and wheat produce the largest nematode populations, whereas sorghum and soybeans produce less than 20% the numbers observed on corn. Scanning electron microscopy reveals that the en face patterns compare to those seen in Pratylenchus pseudocoffeae, P. scribneri, P. hexincisus, and P. alleni. The pattern is described as rectangular to trapezoidal subdorsal and subventral lips adjoining oral disc, but with a clear demarcation between the oral disc and the subdorsal and subventral sectors. A Maximum Likelihood COI tree recognizes P. smoliki as a moderately-well-supported clade with several haplotype subgroups. A Maximum Likelihood partial 28S tree provides strong support for the P. smoliki clade and reinforces the close relationships between species with similar en face patterns. Topotype specimens of P. alleni were demonstrably different from P. smoliki using DNA markers. The geographic range of P. smoliki overlaps with the ranges of P. alleni, P. scribneri, P. neglectus, P. hexicisus, and P. dakotaensis. The observed host range (corn, rye, sunflower, and wheat) suggests that P. smoliki may be native to the tallgrass prairie region of the Great Plains.

Development of Real-Time and Conventional PCR Assays for Identifying a Newly Named Species of Root-Lesion Nematode (Pratylenchus dakotaensis) on Soybean.

A rapid and accurate PCR-based method was developed in this study for detecting and identifying a new species of root-lesion nematode (Pratylenchus dakotaensis) recently discovered in a soybean field in North Dakota, USA. Species-specific primers, targeting the internal transcribed spacer region of ribosomal DNA, were designed to be used in both conventional and quantitative real-time PCR assays for identification of P.dakotaensis. The specificity of the primers was evaluated in silico analysis and laboratory PCR experiments. Results showed that only P.dakotaensis DNA was exclusively amplified in conventional and real-time PCR assays but none of the DNA from other control species were amplified. Detection sensitivity analysis revealed that the conventional PCR was able to detect an equivalent to 1/8 of the DNA of a single nematode whereas real-time PCR detected an equivalent to 1/32 of the DNA of a single nematode. According to the generated standard curve the amplification efficiency of the primers in real-time PCR was 94% with a R2 value of 0.95 between quantification cycle number and log number of P.dakotaensis. To validate the assays to distinguish P.dakotaensis from other Pratylenchus spp. commonly detected in North Dakota soybean fields, 20 soil samples collected from seven counties were tested. The PCR assays amplified the DNA of P.dakotaensis and discriminated it from other Pratylenchus spp. present in North Dakota soybean fields. This is the first report of a species-specific and rapid PCR detection method suitable for use in diagnostic and research laboratories for the detection of P.dakotaensis.

Morphometric and Molecular Diversity among Seven European Isolates of Pratylenchus penetrans.

Pratylenchus penetrans is an economically important root-lesion nematode species that affects agronomic and ornamental plants. Understanding its diversity is of paramount importance to develop effective control and management strategies. This study aimed to characterize the morphological and genetic diversity among seven European isolates. An isolate from the USA was included in the molecular analyses for comparative purposes. Morphometrics of the European P. penetrans isolates generally were within the range of the original descriptions for this species. However, multiple morphometric characteristics, including body length, maximum body width, tail length and length of the post-vulval uterine sac showed discrepancies when compared to other populations. Nucleotide sequence-based analyses revealed a high level of intraspecific diversity among the isolates. We observed no correlation between D2-D3 rDNA- and COXI-based phylogenetic similarities and geographic origin. Our phylogenetic analyses including selected GenBank sequences also suggest that the controversy surrounding the distinction between P. penetrans and P. fallax remains.

Molecular Characterization of Three B-1,4-Endoglucanase Genes in Pratylenchus loosi and Functional Analysis of Pl-eng-2 Gene.

Pratylenchus loosi is an important root-lesion nematode that causes damage to tea plantations in Iran and all over the world. The present study reports on the characterization and evolution of three ß-1,4-endoglucanase genes: Pl-eng-2, Pl-eng-3 and Pl-eng-4. The gene structure of Pl-eng-2 was fully determined with the predicted signal peptide and devoid of the linker domain and carbohydrate-binding domain, while Pl-eng-3 and Pl-eng-4 were only partially sequenced. The transcription of Pl-eng-2 was localized in the secretory esophageal glands of all life stages, but it was upregulated in male and female stages. The exon/intron structures of Pl-eng-2, Pl-eng-3 and Pl-eng-4 confirmed that they resulted from gene duplication followed by sequence and gene structure diversification with loss of the linker domain and carbohydrate-binding domain during evolution. A phylogenetic analysis further confirmed that nematode endoglucanases resulted from the horizontal gene transfer of a bacterial gene, as Pl-eng-3 showed sister relationships with the CelB cellulase of Bacillus subtilis. Silencing Pl-eng-2 by in vitro RNA interference produced a 60% decrease of the transcript level. The reproductive ability of silenced P. loosi showed a 35% reduction of eggs and larval stages compared to untreated nematodes, suggesting that this gene is involved in the early steps of invasion.

Detection of Pratylenchus zeae and P. brachyurus parasitizing plants from the caatinga biome, Ceará, Brazil.

Roots of plants characteristic of the Brazilian caatinga showing necrosis symptoms were observed in Iguatu, CE, Brazil. To identify the species, morphological characterization was performed, through the morphometry of females, and molecular analysis of the ITS and 28S rDNA regions. The nematodes Pratylenchus zeae and P. brachyurus were identified as causal agents, confirming pathogenicity by Koch postulates. This is the first report of P. zeae and P. brachyurus in caaatinga plants in the state of Ceará, Brazil.

Plants Specifically Modulate the Microbiome of Root-Lesion Nematodes in the Rhizosphere, Affecting Their Fitness.

Plant-parasitic nematodes are a major constraint on agricultural production. They significantly impede crop yield. To complete their parasitism, they need to locate, disguise, and interact with plant signals exuded in the rhizosphere of the host plant. A specific subset of the soil microbiome can attach to the surface of nematodes in a specific manner. We hypothesized that host plants recruit species of microbes as helpers against attacking nematode species, and that these helpers differ among plant species. We investigated to what extend the attached microbial species are determined by plant species, their root exudates, and how these microbes affect nematodes. We conditioned the soil microbiome in the rhizosphere of different plant species, then employed culture-independent and culture-dependent methods to study microbial attachment to the cuticle of the phytonematode Pratylenchus penetrans. Community fingerprints of nematode-attached fungi and bacteria showed that the plant species govern the microbiome associated with the nematode cuticle. Bacteria isolated from the cuticle belonged to Actinobacteria, Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, Sphingobacteria, and Firmicutes. The isolates Microbacterium sp. i.14, Lysobacter capsici i.17, and Alcaligenes sp. i.37 showed the highest attachment rates to the cuticle. The isolates Bacillus cereus i.24 and L. capsici i.17 significantly antagonized P. penetrans after attachment. Significantly more bacteria attached to P. penetrans in microbiome suspensions from bulk soil or oat rhizosphere compared to Ethiopian mustard rhizosphere. However, the latter caused a better suppression of the nematode. Conditioning the cuticle of P. penetrans with root exudates significantly decreased the number of Microbacterium sp. i.14 attaching to the cuticle, suggesting induced changes of the cuticle structure. These findings will lead to a more knowledge-driven exploitation of microbial antagonists of plant-parasitic nematodes for plant protection.

Benzoxazinoids selectively affect maize root-associated nematode taxa.

Although the effects of plant secondary metabolites on plant defence have been studied for decades, the exact roles of secondary metabolites in shaping plant-associated microbial and nematode communities remain elusive. We evaluated the effects of benzoxazinoids, a group of secondary metabolites present in several cereals, on root-associated nematodes. We employed 18S rRNA metabarcoding to compare maize root-associated nematode communities in a bx1 knockout maize line impaired in benzoxazinoid synthesis and in its parental wild type. Both genotype and plant age affected the composition of the nematode community in the roots, and the effects of benzoxazinoids on nematode communities were stronger in the roots than in the rhizosphere. Differential abundance analysis and quantitative PCR showed that the root lesion nematode Pratylenchus neglectus was enriched in the bx1 mutant line, while another root lesion nematode, Pratylenchus crenatus, was reduced. Correlation analysis showed that benzoxazinoid concentrations in maize roots mostly correlated negatively with the relative abundance of nematode sequence reads. However, positive correlations between benzoxazinoids and nematode taxa, including several plant-parasitic nematodes, were also identified. Our detailed nematode community analysis suggests differential and selective effects of benzoxazinoids on soil nematodes depending on both the nematode species and the benzoxazinoid compound.

A QTL on the Ca7 chromosome of chickpea affects resistance to the root-lesion nematode Pratylenchus thornei.

The root-lesion nematode Pratylenchus thornei Sher & Allen, 1953 is a damaging parasite of many crop plants, including the grain legume chickpea (Cicer arietinum L.). Within cultivated chickpea, there are no known sources of strong resistance to P. thornei, but some cultivars have partial resistance. In the research reported here, the genetic basis for differences in P. thornei resistance was analysed using a population derived by accelerated single seed descent from a cross between a partially resistant cultivar, PBA HatTrick, and a very susceptible cultivar, Kyabra. A genetic linkage map was constructed from genotyping-by-sequencing data. Two quantitative trait loci were mapped, one on the Ca4 chromosome and one on the Ca7 chromosome. The Ca7 locus had a greater and more consistent effect than the Ca4 locus. Marker assays designed for single nucleotide polymorphisms on Ca7 were applied to a panel of chickpea accessions. Some of these markers should be useful for marker-assisted selection in chickpea breeding. Haplotype analysis confirmed the Iranian landrace ICC14903 to be the source of the resistance allele in PBA HatTrick and indicated that other Australian cultivars inherited the same allele from other Iranian landraces. A candidate region was defined on the Ca7 pseudomolecule. Within that region, 69 genes have been predicted with high confidence. Among these, two have annotations related to biotic stress response. Three others have previously been reported to be expressed in roots of PBA HatTrick and Kyabra, including one that is more highly expressed in PBA HatTrick than in Kyabra. Supplementary Information: The online version contains supplementary material available at 10.1007/s11032-021-01271-8.

Propidium iodide enabled live imaging of Pasteuria sp.-Pratylenchus zeae infection studies under fluorescence microscopy.

Live imaging allows observations of cell structures and processes in real time, to monitor dynamic changes within living organisms compared to fixed organisms. Fluorescence microscopy was used to monitor the dynamic infection process of the nematode parasitic bacterium Pasteuria sp. and the sugarcane root-lesion nematode, Pratylenchus zeae. Under fluorescence microscopy, green-autofluorescent globules were observed in live control and Pasteuria sp.-infected nematodes. Only nematodes killed by Pasteuria sp. or heat treated displayed a diffuse pattern of autofluorescence. Propidium iodide (PI), used as a cell membrane integrity indicator, confirmed that the nematode's cuticle acts as an impermeable barrier. PI stained cells/DNA of heat-treated control and Pasteuria sp.-infected P. zeae. PI as a counterstain facilitated the location of Pasteuria endospores on the cuticle surface of P. zeae. No PI staining was observed in sporangia and in endospores within the nematode body. However, PI specifically stained endospores on the cuticle surface and within the cuticle carcass showing, in mature propagules, a ring-like pattern. Live imaging, combined with fluorescence microscopy and fluorescent dyes such as PI, appears useful in live studies on plant nematode interactions with nematophagous bacteria.