Academic literature on the topic 'Pratylenchus thornei'

Due to Israel’s successful agricultural production and diverse climatic conditions, plant-parasitic nematodes are flourishing. The occurrence of new, previously unidentified species in Israel or of suggested new species worldwide is a consequence of the continuous withdrawal of efficient nematicides. Among plant-parasitic nematodes, migratory endoparasitic species of the genus Pratylenchus are widely distributed in vegetable and crop fields in Israel and are associated with major reductions in quality and yield. This review focuses on the occurrence, distribution, diagnosis, pathogenicity, and phylogeny of all Pratylenchus species recorded over the last few decades on different crops grown throughout Israel—covering early information from nematologists to recent reports involving the use of molecular phylogenetic methodologies. We explore the accepted distinction between Pratylenchus thornei and Pratylenchus mediterraneus isolated from Israel’s northern Negev region, and address the confusion concerning the findings related to these Pratylenchus species. Our recent sampling from the northern Negev revealed the occurrence of both P. thornei and P. mediterraneus on the basis of molecular identification, indicating P. mediterraneus as a sister species of P. thornei and their potential occurrence in a mixed infection. Finally, the efficiencies of common control measures taken to reduce Pratylenchus’ devastating damage in protected crops and field crops is discussed.

Eighteen rangeland plants and 16 weed species were assayed in the greenhouse for efficiency as hosts of Pratylenchus neglectus and P. thornei. Hosting ability ratings were assigned using the ratio of final versus initial nematode density and by comparing the final nematode density to that of susceptible wheat controls. Good hosts of both Pratylenchus spp. included thickspike bluegrass ‘Critana’, smooth brome ‘Manchar’, seven wheatgrasses, and jointed goatgrass. Good hosts of P. neglectus but not P. thornei included two hairy vetches, western wheatgrass ‘Rosana’, big bluegrass ‘Sherman’, tall wheatgrass ‘Alkar’, green foxtail, kochia, large crabgrass, palmer amaranth, redroot pigweed, tumble mustard, and wild oat. Good hosts of P. thornei but not P. neglectus included hard fescue ‘Durar’, sheep fescue ‘Blacksheep’, downy brome, and rattail fescue. Poor or minor hosts of both Pratylenchus spp. included two alfalfas, dandelion, horseweed, lambsquarters, prostrate spurge, and Russian thistle. These assays will provide guidance for transitioning rangeland into crop production and for understanding the role of weeds on densities of Pratylenchus spp. in wheat-production systems.

Thirty crop species and cultivars were assayed in the greenhouse for efficiency as hosts of Pratylenchus neglectus and P. thornei. Hosting ability ratings were assigned using the ratio of final versus initial nematode density and also by comparing the final nematode density to that of a susceptible wheat control. Good hosts of both Pratylenchus spp. included oat ‘Monida’, chickpea ‘Myles’, and lentil ‘Athena’ and ‘Morton’. Good hosts of P. neglectus but not of P. thornei included 10 Brassica spp. (5 canola, 2 mustard, and 3 camelina cultivars), chickpea ‘Sierra’, sudangrass ‘Piper’, and sorghum/sudangrass hybrid ‘Greentreat Plus’. Good hosts of P. thornei but not of P. neglectus included lentil ‘Skyline’ and pea ‘Granger’, ‘Journey’, and ‘Universal’. Poor or minor hosts of both Pratylenchus spp. included chickpea ‘Dwelley’, pea ‘Badminton’, safflower ‘Gila’, ‘Girard’, and ‘KN 144’, sunflower ‘2PD08’, flax ‘Pembina’, eastern gamagrass ‘Pete’, and switchgrass ‘Blackwell’. Results of these assays will provide guidance for improving crop rotation and cultivar selection efficiencies.

Plant-derived phenolic compounds contribute to the defense against various pathogens, including root-lesion nematodes (Pratylenchus spp.). However, there are no reports on the role of phenolic compounds in wheat (Triticum aestivum) against Pratylenchus thornei. In this study, wheat genotypes ranging from resistant to very susceptible to P. thornei were used to investigate the level of total phenols and phenol oxidases, polyphenol oxidase (PPO), and peroxidase (POD) expressed in root tissues when grown in the presence and absence of P. thornei over time (2–8 weeks). Higher constitutive levels of total phenols were found in resistant synthetic hexaploid wheats CPI133872 (576 µg gallic acid equivalent (GAE)/g root) and CPI133859 (518 µg GAE/g root) at 8 weeks after sowing, compared with moderately resistant and susceptible genotypes (192 to 390 µg GAE/g root). The activity of PPO was induced in resistant (CPI133872) and moderately resistant (GS50a and its derivate QT8343) genotypes, becoming maximal at 4 weeks after P. thornei inoculation. The activity of POD was induced in CPI133872 at 6 weeks after P. thornei inoculation. Different genetic sources of resistance to P. thornei showed diverse defense mechanisms and differences in timing responses. The combined effects of total phenols and oxidative enzymes could be important for defense against P. thornei in some resistant wheat genotypes.

Thirteen species of Pratylenchidae: Pratylenchus coffeae, P. delattrei, P. loosi, P. neglectus, P. penetrans, P. pseudopratensis, P. thornei, P. vulnus, Pratylenchus sp., Pratylenchoides alkani, P. ritteri, Hirschmanniella sp. and Zygotylenchus guevarai were collected from different crops and plants throughout Iran. The specimens were identified using morphological and molecular methods. Morphometrics and morphology are given for Pratylenchus sp., P. delattrei, Pratylenchoides alkani and Hirschmanniella sp. The D2-D3 expansion segments of the 28S rRNA gene were amplified and sequenced for all 13 species studied. Diagnostic PCR-ITS-RFLP profiles are given for Pratylenchus delattrei, P. penetrans, P. pseudopratensis, Pratylenchus sp., Pratylenchoides alkani and P. ritteri. Pratylenchus neglectus and P. thornei, collected from cereal fields, P. loosi from tea plantations, P. coffeae from banana, P. penetrans from ornamental plants, P. vulnus from pines and Z. guevarai from almonds showed a high level of similarity in the D2-D3 sequences with corresponding GenBank sequences. Nucleotide differences between Iranian populations and reference species were in the intraspecific range. Pratylenchus delattrei, found in vegetable fields, and Pratylenchus sp. from palm rhizosphere, formed a highly supported clade with P. zeae, the two former species being morphologically very close to the latter except in tail shape. Pratylenchus pseudopratensis, from cereal fields, clustered with P. vulnus with low support. Phylogenetic relationships within Pratylenchus species were mainly congruent with those obtained in previous studies. Despite the morphological similarities between P. ritteri and P. alkani, the D2-D3 of 28S rRNA gene sequences differed by 5 bp. Hirschmanniella sp., from a rice field, formed a clade with H. loofi and H. kwazuna.

Summary The root-lesion nematode, Pratylenchus thornei, attacks a wide range of crops and causes significant reductions in global grain production. Breeding programmes are currently restricted to using parents with moderate resistance to P. thornei as cereal cultivars with complete resistance are yet to be identified. This study evaluated 484 of CIMMYT’s spring wheat accessions for resistance to P. thornei of which 56 lines were pre-identified as resistant under controlled growth room conditions. These lines were further evaluated for their resistance and tolerance reactions under field conditions, where 14 accessions maintained their resistance and 16 were moderately resistant against P. thornei. Four lines gave excellent resistant and tolerance reactions to P. thornei. The relationship between the nematode reproduction factor (Pf/Pi) and wheat grain yield in field experiments fits a linear regression model. These findings could be useful for improving P. thornei resistance in wheat.

Summary The goal of this study was to evaluate the efficiency of Pasteuria thornei as a biological seed treatment for Pratylenchus brachyurus control in soybean (Glycine max). Seeds of soybean ‘SYN1080’ were treated with three concentrations of P. thornei endospores per seed (5 × 106, 107, 1.5 × 107), together with two other treatments for comparison: a commercial control containing abamectin (0.58 mg seed−1) and a mixed treatment containing abamectin (0.58 mg seed−1) and 107 endospores of P. thornei. These seeds were sown in plastic cups containing soil inoculated with 1000 nematodes (Trial 1) and 600 nematodes (Trial 2). The trials were evaluated at 60 and 90 days after inoculation (dai). The total of nematodes extracted from the roots of each plant was used as the assessment criterion. Only the highest concentration of P. thornei endospores (1.5 × 107) consistently reduced the final populations of P. brachyurus by 25-50% compared to the non-treated seeds. The treatments containing abamectin were superior in reducing the nematode population in all trials and evaluations. There was no visible synergistic effect of the combined use of abamectin and P. thornei in the same treatment at 90 dai.

The root lesion nematode Pratylenchus thornei causes economic losses in wheat and barley internationally through both reduced grain yield and grain quality. This study investigated the relationships between the presowing P. thornei density and grain yield and the postharvest nematode densities. Four field experiments were conducted at the same site between 2010 and 2014. A range of presowing P. thornei densities was established in the first year by growing three cereal cultivars that ranged from resistant to susceptible. In the following year, plots were sown with the five same cereal cultivars. A linear relationship was observed between the natural log of the presowing P. thornei density and grain yield across all seasons. The results showed that grain yield losses varied between cultivars and seasons. The importance of season was significant, with this study conducted over several seasons, and it highlighted the variability in yield losses between seasons, which will need further investigation. The greatest yield losses observed were 25 to 28% when the maximum presowing P. thornei densities ranged between 150 and 250 P. thornei g of soil−1. An analysis of the relationship between the presowing and postharvest nematode densities revealed that increased presowing nematode densities resulted in decreased multiplication rates in all seasons and in all cultivars. Nematode multiplication rates also varied between seasons. These results explain why it is difficult to predict nematode levels based on cropping history, and additionally, they highlight the importance of growing resistant cultivars to maintain low levels of P. thornei to minimize risk of yield losses.

The root-lesion nematode Pratylenchus thornei is one of the most important pests restricting productivity of wheat in the Pacific Northwest (PNW). It is laborious and difficult to use microscopy to count and identify the nematodes in soils. A SYBR Green I-based real-time polymerase chain reaction (PCR) assay was developed to detect and quantify this species from DNA extracts of soil. A primer set, designed from the internal transcribed spacer region (ITS1) of rDNA, was highly specific to P. thornei and did not amplify DNA from 27 isolates of other Pratylenchus spp., other nematodes, and six fungal species present in PNW wheat fields. A standard curve relating threshold cycle and log values of nematode number was generated from artificially infested soils. The standard curve was supported by a high correlation between the numbers of P. thornei added to soil and the numbers quantified using real-time PCR. Examination of 15 PNW dryland field soils and 20 greenhouse samples revealed significant positive correlations between the numbers determined by real-time PCR and by the Whitehead tray and microscopic method. Real-time PCR is a rapid, sensitive alternative to time-consuming nematode extractions, microscopic identification, and counting of P. thornei from field and greenhouse soils.

The root lesion nematode (RLN), Pratylenchus thornei, is a biotrophic migratory pest of plant roots and its infestation causes losses in many economically important crops. RNA interference (RNAi) is a naturally occurring eukaryotic phenomenon and can be used to silence parasitism effector genes of P. thornei using host-mediated RNAi. This may be developed as an environmentally friendly and a cost-effective control strategy. The overall aims of this research were to investigate the effects of in vitro and in planta RNAi silencing of putative P. thornei parasitism effector genes, and their nematicidal effects in two host plants. Five putative target parasitism genes vital for nematode entry into roots (Pt-Eng-1, Pt-PL), feeding (Pt-CLP) and suppressing host defence responses (Pt-UEP, Pt-GST) were identified, validated in silico using comparative bioinformatics, cloned into suitable in vitro transcription and binary vectors, and advanced to RNAi studies. Partial sequences for four of these target effector genes (Pt-Eng-1, Pt-PL, Pt-CLP, Pt-GST) were identified using Rapid Amplification of cDNA (RACE) PCRs and annotated in silico. Protein families, conserved domains, taxonomic and phylogenetic relationships for all four effectors were studied. This sequence information will help inform future investigations involving gene expression and proteomics of the selected putative effectors. In vitro RNAi was used for functional characterisation of the five effector sequences. Effects on nematode phenotype, behaviour, gene expression, and longer-term effects on reproduction were assessed after soaking nematodes in dsRNA through infection of healthy wild type soybean and alfalfa roots. Soaking of mixed stage P. thornei in 1mg/mL dsRNA of target genes for 16 h did not cause phenotypic changes except for Pt-PL, which exhibited straight or slightly curved phenotypes after soaking compared to the normal sigmoid body movement, also evident for green fluorescent protein (gfp) and no dsRNA treated controls. Semi-quantitative PCRs and densitometry analysis revealed a significant reduction of transcript accumulation for all five putative parasitism effector genes. Longer-term effects assessed at 21 dpi reduced nematode reproduction by 40 to 70% for all target genes compared to respective control treatments suggesting that the effectors studied were required for nematode infectivity, survival or reproduction. In planta RNAi involved Agrobacterium-mediated plant transformations to develop axenic transgenic hairy root events of soybean (Glycine max var. Williams 82) and alfalfa (Medicago sativa), and non-axenic hairy roots (composite plants) of soybean. Both hosts were amenable to Agrobacterium-mediated transformation, but hairy root induction was faster in alfalfa than soybean. However, more events were generated for soybean than alfalfa. Transgenic hairy roots confirmed by molecular analyses were challenged with P. thornei and their presence confirmed after 14 dpi. After 21 dpi, nematode numbers and transcript abundance was assessed using semi-quantitative PCRs and densitometry analysis. Host-mediated silencing of the five putative parasitism effector genes using transgenic soybean and alfalfa hairy roots showed a significant reduction in target transcript accumulation and approximately 38 to 75% reduction in P. thornei numbers compared to untransformed wild-type controls. For some events, there was a positive correlation between reduced transcripts and nematode numbers. Based on percent reduction in transcript accumulation of the target genes relative to 18S rRNA as assessed by densitometry, the extent of gene knockdown measured (from most to least) was: Pt-Eng-1, Pt-PL, Pt-CLP, Pt-UEP, and Pt-GST. Similarly, Pt-Eng-1, Pt-PL and Pt-CLP were ranked in the same order, from the lowest to highest reproduction on soybean and alfalfa, indicating a positive correlation between the level of knockdown and reduced reproduction. In soybean, these genes were followed by Pt-GST and Pt-UEP for the percentage of reproduction recorded, whereas, in alfalfa, reduction in reproduction for these two target genes did not differ significantly. Composite soybean with wild-type shoots and transgenic hairy roots expressing Pt-Eng-1 and Pt-PL genes were developed and provided an opportunity to test the effectiveness of silencing target genes in planta and on nematode numbers in conditions that mimicked natural host infections. For both Pt-Eng-1 and Pt-PL genes, there was a significant reduction in percentage of transcript accumulation relative to 18S rRNA, which correlated with a reduction in nematode numbers by 53.4% and 48.5% for Pt-Eng-1 and Pt-PL, respectively. The amenability of P. thornei to host-mediated RNAi using effector gene sequences, and the overall results of this study, point towards the potential use of this technology to control P. thornei and related RLN species effectively in different host crops.

The Pasteuria genus comprises gram-positive bacteria that are obligate parasites of arthropods and nematodes. Species of this genus are ubiquitous, being present in both aquatic and terrestrial environments all around the world. Pasteuria was first described as a genus at the end of the 19th century and has undergone considerable reclassification regarding its member species. Starting in the 1980s, a more meticulous classification effort regarding the identification of Pasteuria spp., and its parasitic habits began. These studies were strongly motivated by the ability of individuals of this genus to parasitize phytopathogenic nematodes of several plant species. Each species of the genus Pasteuria establishes a strict parasitic relationship with a specific genus of phytonematode. As an example of this interaction, Pasteuria thornei is a parasite restricted to the genus Pratylenchus, which comprises the nematodes popularly known as root-lesion-nematodes, a pest of several agronomically important crops. Considering the current relevance of studies involving the biological control of phytonematodes, in the present work three experiments were carried out, each one containing a replicate, totaling, therefore, six experiments. Two experiments were intended to verify the efficacy of P. thornei as a biological control agent (BCA) of Pratylenchus brachyurus in soybean. The remaining four experiments had a similar objective in the scope of the Pratylenchus zeae - maize pathosystem. Two experiments were carried out to verify the efficacy of P. thornei as a biological control agent for P. zeae in maize, and afterwards, two additional experiments were performed in order to verify the capacity of the BCA to reduce productivity losses in corn plants due to the parasitism of this nematode. For the soybean experiments, the following treatments were added to the seeds of the cultivar SYN1080: three different concentrations of P. thornei endospores per seed (5x106, 107 e 1,5x107), a commercial control group for comparison containing abamectin (0.58mg/seed) and a mixed treatment containing abamectin (0.58 mg / seed) and 107 P. thornei endospores. Untreated seeds were used as a control group. The treatments were sown in 500 cm3 plastic cups containing soil inoculated with 1000 nematodes (experiment 1) and 600 nematodes (experiment 2). Fresh root mass and nematodes extracted from the roots of each plant were used as parameters of evaluation, taking place 60 and 90 days after inoculation (DAI). Only the treatment with the highest concentration of P. thornei (1.5x107) reduced the final population of nematodes significantly, reaching 30-50% of reduction compared to the untreated seeds. However, treatments containing the commercial control abamectin were superior in reducing the final population of nematodes in all experiments evaluated. Regarding the maize efficacy experiments, CELERON hybrid seeds were treated as described: four concentrations of P. thornei endospores per seed (5x106, 107, 1,5x107, 2x107), a commercial control group for comparison containing abamectin (0.58 mg / seed) and a mixed treatment containing abamectin (0.58 mg / seed) and 107 P. thornei endospores. Untreated seeds were used as a control group. The treated maize seeds were planted in 500 cm3 plastic cups containing soil inoculated with 4000 and 1000 individuals for the efficacy experiments 1 and 2, respectively. Evaluations occurred at 60 and 90 DAI. For the productivity assays, the experiments 3 and 4 were carried out under a screened greenhouse, with experimental plots consisting of 9L pots filled with artificially infested soil. Seeds of the CELERON hybrid received the following treatments: abamectin (0.58mg / seed), P. thornei (107 endospores / seed) and mixed treatment containing both abamectin (0.58mg / seed) and P. thornei (107 endospores / seed). Two additional treatments containing untreated seeds served as controls, with and without the presence of Pratylenchus zeae. The evaluation measured several agronomic traits, such as dry weight of the aerial parts, fresh mass of roots at harvest and total weight of grains. In addition, the nematode population was measured in fresh roots at 45, 90 days and at the time of harvest. Efficacy trials showed that the highest concentrations of P. thornei (1.5x107 and 2x107) have a considerable potential of P. zeae control. The nematode population reduction was 54 and 47% in experiments 1 and 2, respectively, for the highest P. thornei concentration treatment. The commercial formulation containing abamectin showed a reduction of P. zeae population above 90% in both experiments. Regarding the maize productivity experiments, control potential of nematodes by P. thornei was similar to that observed in the efficacy study. The treatments containing abamectin had an effect on the mitigation of yield losses caused by P. zeae in both experiments. The mixed treatment (abamectin and P. thornei) and the one containing exclusively P. thornei presented a positive performance in both replicates. In none of the experiments synergistic or additive effects were observed between P. thornei and abamectin. With the data obtained in these experiments, the control potential of P. thornei on P. brachyurus and P. zeae in soybean and corn, respectively, is evident. Additionally, P. thornei and abamectin in the form of seed treatment, show potential in mitigating yield losses caused by P. zeae in maize. This highlights the importance of P. thornei as an additional tool for the management of root lesion nematodes in soybean and maize, and should encourage subsequent work.
O gênero Pasteuria compreende bactérias gram-positivas parasitas obrigatórias de artrópodes e nematoides. A distribuição das espécies deste gênero pelo mundo é ubíqua, podendo ser encontradas em ambientes aquáticos e terrestres. Este gênero foi descrito no final do século XIX e sofreu consideráveis reclassificações em relação às espécies nele compreendidos. A partir da década de 80, deu-se início a um esforço de classificação mais minucioso com relação à identificação de Pasteuria spp. e seus hábitos parasitários. Estes estudos foram motivados, principalmente, pela capacidade dos indivíduos deste gênero em parasitar nematoides fitoparasitas de diversas culturas. Cada espécie do gênero Pasteuria estabelece relações parasitárias com um gênero específico de fitonematoide. A exemplo desta interação, Pasteuria thornei é um parasita restrito ao gênero Pratylenchus, que compreende os nematoides causadores das lesões radiculares, daninhos a diversas culturas de importância agronômica. Considerando a relevância atual de estudos envolvendo o controle biológico de fitonematoides, no presente trabalho foram realizados três experimentos, cada um contendo uma réplica em época distinta, totalizando, portanto, seis experimentos. Dois experimentos tiveram por objetivo verificar a eficácia de P. thornei como agente de controle biológico (ACB) de Pratylenchus brachyurus na cultura da soja. E os demais quatro experimentos abordaram o patossistema Pratylenchus zeae-milho. Para esse objetivo, foram realizados dois experimentos com o intuito de verificar a eficácia de P. thornei como agente de controle biológico de P. zeae em milho, e outros dois experimentos para testar a capacidade do ACB em reduzir a perda de produtividade em plantas de milho decorrente do parasitismo do nematoide. Para os experimentos de soja, às sementes da cultivar SYN1080 foram adicionados os tratamentos como se segue: três concentrações de endósporos de P. thornei por semente (5x106, 107 e 1,5x107), um grupo de controle químico comercial para comparação contendo abamectina (0,58 mg / semente) e um tratamento misto contendo abamectina (0,58 mg / semente) e 107 endósporos de P. thornei. Sementes não tratadas foram utilizadas como testemunha. As sementes tratadas foram semeadas em copos de plástico de 500 cm3 contendo solo inoculado com 1000 nematoides (experimento 1) e 600 nematoides (experimento 2). A massa de raiz fresca e os nematoides extraídos das raízes de cada planta foram utilizados como critério de avaliação dos experimentos, a qual foi realizada aos 60 e 90 dias após a inoculação (DAI). Apenas o tratamento com a maior concentração de P. thornei (1,5x107) reduziu a população final de nematoides de maneira significativa atingindo 30-50% de redução, comparado àquele contendo sementes não tratadas. No entanto, os tratamentos que contém abamectina foram superiores na redução da população final de nematoides em todos os experimentos avaliados. Em relação aos experimentos de eficácia em milho, sementes do híbrido CELERON foram tratadas como explicitado: quatro concentrações de endósporos de P. thornei por semente (5x106, 107, 1,5x107 e 2x107), um grupo de controle comercial para comparação contendo abamectina (0,58 mg / semente) e um tratamento misto contendo abamectina (0,58 mg / semente) e 107 endósporos de P. thornei. As sementes tratadas de milho foram semeadas em copos de plástico de 500cm3 contendo solo inoculado com 4000 e 1000 indivíduos para os experimentos de eficácia 1 e 2, respectivamente. As avaliações ocorreram aos 60 e 90 DAI. Para os estudos de produtividade, foram realizados os experimentos 3 e 4 sob um telado com parcelas experimentais constituídas por vasos de 9L preenchidos de solo infestado artificialmente. Sementes do híbrido CELERON foram utilizadas contendo os seguintes tratamentos: abamectina (0,58mg / semente), P. thornei (107 endósporos/semente) e um tratamento misto contendo abamectina (0,58mg / semente) e P. thornei (107 endósporos/semente). Dois tratamentos adicionais contendo sementes não tratadas serviram de testemunhas, com e sem Pratylenchus zeae. A avaliação consistiu na medição de várias características agronômicas, como peso seco da parte aérea, massa fresca de raízes no momento da colheita e peso total dos grãos. Adicionalmente, foi mensurada a população de nematoides em raízes frescas aos 45, 90 dias e no momento da colheita. Os ensaios de eficácia mostraram que as concentrações mais elevadas de P. thornei (1,5x107 e 2x107) possuem um potencial mensurável de controle de P. zeae. A redução da população de nematoides foi de 54 e 47% nos experimentos 1 e 2, respectivamente. A formulação comercial de abamectina mostrou uma redução da população de nematoides superior a 90% em ambos os experimentos. No que diz respeito aos experimentos de produtividade de milho, o potencial de controle de nematoides por P. thornei foi semelhante ao observado no estudo de eficácia. O tratamento com abamectina teve efeito na redução das perdas de rendimento causadas por P. zeae em ambos os experimentos; assim como os tratamentos misto (abamectina e P. thornei) e aquele contendo apenas P. thornei que apresentaram desempenho positivo em ambas as repetições. Em nenhum dos experimentos foi observado efeito sinérgico ou aditivo entre P. thornei e abamectina. Com os dados obtidos nestes experimentos, fica evidente o potencial de controle de P. thornei sobre P. brachyurus e P. zeae em soja e milho, respectivamente. Ainda, tanto P. thornei quanto abamectina apresentam o potencial de mitigar as perdas de rendimento causadas por P. zeae em milho através do tratamento de sementes. Isso evidencia a importância de P. thornei como uma ferramenta adicional para o manejo desses nematoides, e deve encorajar trabalhos subsequentes.

Bibliography: leaves 224-236. The study aimed to determine the distribution of both P. thornei and P. neglectus in South Australia. Also to study the field and laboratory population dynamics of P. thornei in relation to wheat yields, to determine its host range on a variety of cereal and non-leguminous hosts and to identify possible sources of nematode resistant wheat cultivars/varieties. Preliminary experiments studied the involvement of root rotting fungi with the nematode in wheat disease.

Root lesion nematode (Pratylenchus thornei) is a relatively new problem in the wheat growing areas of central and northern New South Wales. Despite this, the nematode has become endemic on heavy clay soils which have a long history of wheat production. The objectives of the research reported in this thesis were to investigate the influence of environmental factors on the population dynamics and distribution of P. thornei, and the tolerance and resistance of commercial cultivars and advanced breeding lines to the nematode. The population dynamics of the nematode were investigated in 1989, 1990 and 1991 by sampling a wheat field at monthly intervals. P. thornei populations remained static for a three month period following sowing, then increased in October. The increase in nematode populations was correlated with increases in soil temperature in 1989 and 1990. The influence of soil temperature on the multiplication and development of P. thornei was investigated in a growth chamber study at three temperatures; 10, 20 and 30 °C. Nematode populations developed slowly at 10 °C, increased rapidly and then declined at 30 °C and increased in an exponential pattern at 20 °C. In the 20 °C treatment wheat shoot growth was correlated to nematode populations, with increasing populations increasing shoot weight until nematodes exceeded 3000 per g of root. Root weights at 20 °C declined with increasing nematode populations. The distribution of P. thornei in a wheat field was investigated over two consecutive years in 1989 and 1990 by taking regular monthly samples 4 m apart on a 0.23 ha grid. The aggregation of the nematodes was close to random at the time of sowing, however, as the nematodes multiplied the distribution patterns became aggregated, with areas of very high populations. The areas of dense nematode populations could not be correlated to any plant or edaphic factor. However, the consistent seasonal nematode aggregation was shown to part of the nematode biology and allowed a sampling protocol to be developed which could be linked to sampling errors, depending on the precision of the field mean required. Twenty seven fields in northern NSW were sampled prior to sowing winter crops and again at harvest. Soil physical factors were not found to be correlated with initial nematode populations or multiplication of nematodes. However, the cropping history and the previous crop prior to sampling were found to be major factors influencing the initial population of nematodes at sowing. Continual cultivation of susceptible crops, such as wheat and legumes was found to increase the nematode population at the time of sowing. A study of thirty six cereal cultivars at two sites near Narrabri in northern NSW identified problems with the use of nematicides as a control when studying tolerance reactions of cereals. Differences in soil characteristics between the two sites and in genotype reactions to the nematicide were identified as the main causes of variation in cereal tolerance reactions to P. th o rn ei. Resistance to P. thornei was measured as the multiplication of nematodes from sowing to harvest. The initial population of nematodes at the time of sowing was identified as an important covariate influencing multiplication rates of the nematodes. Resistant cereals with good tolerance to P. thornei were identified as barley and durum wheat, as well as three breeding lines; SUN 289 A, SUN 290 B and SUN 277 A. From the studies of this thesis sustainable wheat production in northern NSW where P. thornei was identified as a potential problem was possible using an integrated management system. This involves crop rotation to non-host crops and quantifying nematode populations before sowing wheat crops to assess the risks of yield losses. As part of a management system wheat crops should be sown early to allow for maximum root development before nematodes multiply in warmer soils and where possible, tolerant and resistant wheat varieties grown.

Root lesion nematodes of the genus Pratylenchus feed and reproduce in the root cortex of many plant species, including wheat. Migration through root tissue causes extensive root damage, and in turn severe reductions in growth and yield. In Australia, one of the most prevalent and widespread species affecting wheat is Pratylenchus thornei. Due to the wide host range of Pratylenchus spp. and the restrictions and inefficiency of chemical pesticides, the development of resistant cultivars has become increasingly important. Despite the identification and investigation of several resistance sources and resistance quantitative trait loci (QTL), no P. thornei resistance has been integrated into commercial cultivars. In addition, prior to this study, the biological resistance mechanisms of wheat against P. thornei were not well characterised. The identification of novel sources of genetic resistance in wheat and understanding of the biological mechanisms will allow effective combinations of genes either to be used alternatively or pyramided to generate effective and stable Pratylenchus resistance. The major objectives of the study were to identify genetic loci associated with P. thornei resistance and to investigate the associated biological mechanisms in a double haploid wheat population developed from a cross between the synthetically derived Sokoll and the Australian adapted Krichauff parental lines. The resistance to P. thornei observed in the Sokoll x Krichauff wheat population is complex and under the control of several loci which suppress all nematode developmental stages. The four main components of the root invasion process by Pratylenchus: root attraction, penetration, endoparasitic feeding and reproduction, were investigated to determine the location, timing and role of resistance against P. thornei. Through analysing root invasion by each nematode life stage, it was shown that resistance in the Sokoll x Krichauff population occurs post penetration to suppress P. thornei motility/migration and juvenile development causing reduced reproduction (egg deposition and hatch). Attraction and penetration assays were conducted on seedlings grown both in sand and on agar. There was no significant difference in the rate at which P. thornei was attracted towards resistant or susceptible roots in sand. However on agar, when both genotypes were present, there was a significantly higher attraction towards the susceptible roots indicating resistant roots may secrete repellent or toxic compounds during pre-penetration or that susceptible roots secrete more attractants. The penetration rates of P. thornei in resistant and susceptible roots, both on agar and in sand, did not significantly differ. No preferred root penetration zone was observed with P. thornei, but penetration was not random as nematodes were attracted to root regions previously invaded. In concordance with other Pratylenchus studies, resistance to P. thornei in this Sokoll x Krichauff population acts post penetration. Analysis of P. thornei development in the resistant and susceptible genotypes showed that significantly fewer P. thornei nematodes of all stages occurred in the resistant compared to the susceptible roots. Juvenile development was suppressed as no juvenile stage two nematodes (J2) were present 35 days after inoculation in resistant genotypes. At 45 days after inoculation, forty times more P. thornei juvenile stage three (J3) were present in the susceptible than the resistant parent. Unlike other studies where resistance against Pratylenchus caused nematodes to exit roots, in this study, similar numbers of P. thornei J2 were still present within the resistant roots 10 days after inoculation, indicating that resistance suppresses nematode development rather than causing nematodes to leave resistant roots. The inhibition of juvenile development resulted due to the suppression of nematode migration/motility which suppressed feeding but also due to reduced egg deposition and hatch. Simple and inexpensive assays were designed to investigate P. thornei motility, egg hatch and deposition in root exudates/extracts and roots grown on agar. Significantly higher numbers of P. thornei nematodes became non-motile when exposed to root exudates from resistant (65%) versus susceptible (30%) roots after exposure for 3 days. The effects of these compounds were found to be reversible and to specifically affect P. thornei but not Pratylenchus neglectus. In migration assays, P. thornei only migrated a small distance through the resistant root cortex from the point of inoculation (10 mm), but further in the susceptible roots (70 mm). Pratylenchus thornei reproduction was also affected by resistance. Egg deposition was up to 30% less within resistant than in the susceptible lines. About 40% less hatch occurred from eggs within and adjacent to roots of resistant versus susceptible seedlings. Similarly, hatching was decreased by 10% in resistant root exudate compared to the susceptible after 10 days of exposure. An increased hatch after dilution of root exudates and a lower hatch in resistant versus the absence of roots, indicates the presence of hatching inhibitor compounds. As these root exudates were derived from plants not exposed to Pratylenchus/other pathogens, this indicates resistant genotypes constitutively produce compounds that inhibit motility and reproduction. In order to identify QTL and develop molecular markers accounting for the observed resistance, a genetic map was constructed from the Sokoll x Krichauff doubled haploid population comprising 150 lines. A total of 860 Diversity Array Technology markers and 111 microsatellite markers were used to assemble the genetic map. Two highly significant P. thornei resistance QTL were identified on chromosomes 2BS and 6DS, QRlnt.sk-2B.1 and QRlnt.sk-6D, explaining 24 and 43% of the phenotypic variation, respectively. These QTL mapped to chromosome regions previously identified to be associated with Pratylenchus resistance, based on common marker locations. Two significant QTL were also identified on chromosomes 4A and 5A, explaining 6 and 9% of the phenotypic variation. The population was fixed for the effects of the highly significant QTL on 2BS and 6DS and further QTL were identified on chromosomes 2B, 2D, 3A, 5B and 6B. The QRlnt.sk-2B.1 and QRlnt.sk-6D account for a large portion of the observed resistance, showing that in this population the Sokoll derived resistance to P. thornei is very strong and is controlled by a few loci with large effects. There are considerable financial and labour costs associated with Pratylenchus phenotypic screening methods. Molecular markers employed through marker assisted selection will eliminate the need for large scale phenotyping in breeding programs and thus accelerate the development and availability of resistant cultivars. The microsatellite marker barc183 linked to QRlnt.sk-6D is also associated with P. thornei resistance in other mapping studies in different genetic backgrounds and thus highlights the potential benefit of this marker for use in marker assisted selection. However, the highly significant QTL on 2BS and 6DS currently span large chromosomal regions, thus fine mapping is required to delimit the QTL interval to establish more closely linked markers before they can be utilised in breeding programs. The ultimate aim of this project was to correlate a biological role with an identified P. thornei resistance QTL. Thus, in order to identify whether the QTL linked to P. thornei were associated with the observed motility and hatch inhibition, a subset of the population was phenotyped using the motility and hatching assays designed in this study. Suggestive QTL were identified on chromosomes 2B, 5B, 6B and 6D linked to hatching and motility suppression, which co-located to the P. thornei resistance QTL identified in this and previous studies. Although only suggestive, alignment with other QTL indicates that these resistance QTL may play a role in inhibiting P. thornei motility or juvenile hatching. To further define and confirm these QTL, phenotypic analysis needs to be performed on the entire population. The biochemical characteristics of the preformed resistant root compounds causing motility and hatching suppression were investigated. Root exudates that were subjected to heat/cold treatments caused less motility suppression than compared to the untreated control, indicating these resistant root compounds are water soluble and fairly stable in nature. Flavonoids, oxidised phenols and peroxidases associated with insect resistance genes that co-located with the hatching and motility suppression QTL and the P. thornei resistance QTL regions have been implicated in other Pratylenchus-plant resistance interactions. These results indicate a potential role for these compounds in the P. thornei resistance observed in Sokoll x Krichauff. Further investigation is required to define the chemical nature and specific roles of resistant root compounds in the suppression of nematode development. The results of this study show that the resistance observed in the Sokoll x Krichauff wheat population to P. thornei is complex and under the control of two highly significant and several minor loci, which do not affect penetration but suppress nematode feeding, development and reproduction.
Thesis (Ph.D.) -- University of Adelaide, School of Agriculture, Food and Wine, 2013

Includes Appendix 1 -- Appendix 2 -- Movie Clip 6.1
The root lesion nematode Pratylenchus thornei feeds on roots of wheat (Triticum aestivum) plants, causing significant damage to the roots at the cellular level, resulting in yield reduction. In a previous study, P. thornei resistance QTL, QRlnt.sk-6D and QRlnt.sk-2B were identified in a Sokoll/Krichauff wheat DH population. The current project was undertaken with the aim to dissect the genetic and biological basis of this resistance. To better define the genetic basis of resistance, both resistance loci were fine mapped using the Sokoll/Krichauff DH population and six newly developed RIL populations. Bulked segregation analysis with the 90K Wheat SNP array identified linked SNPs, which were subsequently converted to KASP assays for mapping in the DH and RIL populations. QRlnt.sk-6D was delimited to a 3.5 cM interval, representing 1.77 Mbp in the bread wheat cv. Chinese Spring reference genome sequence and 2.29 Mbp in the Ae. tauschii genome sequence. These intervals contained 42 and 43 gene models in the respective annotated genome sequences. QRlnt.sk-2B was delimited to 1.4 cM, corresponding 3.14 Mbp in the durum wheat cv. Svevo reference sequence and 2.19 Mbp in Chinese Spring. The interval in Chinese Spring contained 56 high confidence gene models. Intervals for both QTL contained genes with similarity to those previously reported to be involved in disease resistance, namely genes for phenylpropanoid-biosynthetic-pathway-related enzymes, NBS-LRR proteins and protein kinases. The potential roles of these candidate genes in P. thornei resistance are discussed. The KASP markers reported in this study could potentially be used for marker assisted breeding of P. thornei resistant wheat cultivars. To quantify P. thornei from wheat root, a qPCR-based assay was developed. A standard curve was produced to quantify P. thornei from wheat root samples. The standard curve was validated by estimating P. thornei from sixteen wheat lines with known levels of resistance. Overall, the assay was 2.4-fold less expensive compared to the commercial service (PreDicta B test, SARDI). The DNA extraction protocol was inexpensive as it works without using a commercial DNA extraction kit. In order to identify metabolites associated with resistance loci, the GC-MS based metabolic profiles of root exudates and root tissues from the resistant lines were compared with the susceptible lines. In root exudates, 21 metabolites were found to be associated with resistance QTL. Likewise, from root tissue, 15 metabolites were found to be associated with the resistance QTL. These metabolites were derived from diverse biochemical groups, including amino acids and amines, organic acids, sugars, sugar alcohols and sugar phosphates. The possible roles of these resistance compounds in P. thornei resistance is largely unknown. However, their nematotoxic properties against other plant parasitic nematodes were discussed. In response to P. thornei infection, the histological and histochemical responses of wheat roots were investigated. The use of the fluorescent dye PKH26 (for P. thornei labelling) and confocal microscopy enabled visualisation of live P. thornei both out and inside wheat root tissue. In response to P. thornei infection, secondary cell wall thickening (deposition of cellulose, callose, lignin and suberin) was observed in the P. thornei resistant cultivar, Sokoll. Secondary cell wall thickening might result in physical reinforcement of the cell wall restricting P. thornei migration in the resistant root tissues.
Thesis (Ph.D.) -- University of Adelaide, School of Agriculture, Food & Wine, 2020

Plant parasitic nematodes infect almost all crop plants and annually cause losses of millions of dollars worldwide. The relationship between these pathogens and their hosts is still poorly understood in spite of several decades of research. In this research project, I attempted to investigate different aspects of this host-parasite relationship with respect to root-parasitic nematodes, and the effect these nematodes have on growth and development of the affected plants. I studied the host-parasite interactions using two different host plants, Arabidopsis thaliana and Solanum lycopersicum, and two nematodes which contrasted in their modes of infection, life cycle and pathogenicity: the root-knot nematode, Meloidogyne javanica, and the root lesion nematode, Pratylenchus thornei. Studies on A. thaliana were conducted in the laboratory under aseptic conditions in Petri dishes, and studies on tomato were conducted in the greenhouse as pot culture experiments. In my first investigation I examined the changes occurring in the cytoskeleton of A. thaliana root cells due to infection by M. javanica and P. thornei. This experiment was conducted over a period of one year from March 2003 to March 2004 at the Research School of Biological Sciences, Australian National University, Canberra, ACT in the laboratory of Drs Geoff Wasteneys and David Collings. The plant cytoskeleton plays a vital role in almost all cellular functions including cell signalling, cell division and wound response. I used three different investigative techniques to compare the effects of plant parasitic nematodes on the host root cytoskeleton. These techniques were whole root double immunolabelling, double immunolabelling of BMM sections and use of GFP-hTalin-transformed A. thaliana. Samples were observed using confocal laser scanning microscopy. I found all three techniques to be effective in studying cytoskeletal changes in infected roots. Whole root immunolabelling and GFP-hTalin-transformed A. Thaliana were most useful for studying the early stages of infection. However, immunolabelling of BMM sections was most effective in the later stages of infection to study large and thick gall tissue, as the transmission of light through thick tissue was not adequate to obtain high quality images by the other two techniques. Whole root immunolabelling showed that both M. javanica and P. thornei initially (even within the first 3 h) caused similar changes in A. thaliana. All stages of M. javanica were observed in A. thaliana roots; their migration and development was observed for 14 d. However, observations on P. thornei could not be conducted beyond the first 24 h after inoculation due to bacterial contamination. While P. thornei damaged A. thaliana roots, they were not observed within roots at any stage during this observation period. This was probably because the small diameter of the roots made them unattractive for entry by this larger nematode species. Material labelled for actin was observed to accumulate in a rounded or disc-shaped plug on the root surface and appeared to line the wound surface on the inside of the cell within the first 24 h after inoculation. Microtubules maintained their orientation, giving support to the cell wall. Increased actin and microtubule labelling was detected in nematode-infected root tissue with all three techniques used. In A. thaliana roots inoculated with M. javanica, this was especially prominent during initial entry and feeding site formation but was not as noticeable during nematode migration. This may have been due to a change in permeability of the cell walls resulting from nematode infection. A diffuse fluorescence was observed whenever actin fixation was not adequate. Once the M. javanica nematode entered the root, it followed a path (probably associated with physiological or chemical signals derived from the different cell types) during different stages of its migration to reach its ultimate feeding site. Microtubules in host cells close to the nematode body in its migration path were in a wavy, rather than a taut, arrangement. In nematode feeding sites, giant cells were formed around the head of the nematode and numerous small cells were observed towards the posterior of the nematode, forming the gall. Unusual divisions were observed in nematode-infected root tissues, with abnormal spindles and incomplete phragmoplasts in a region where cell divisions do not normally occur. Using immunolabelled BMM sections I observed well-defined microtubules and actin bundles in an infected cell. Giant cells appeared to have lost their growth polarity and anisotropy. These giant cells were spindle-shaped, with two tapering ends and with an enlarged middle section, indicating that there may be significant differences between the end (cross) walls of cells and the walls parallel to the longitudinal axis of the root. I subsequently conducted a temporal investigation in tomato, as an adjunct to a pot trial, to determine the similarities and differences in the way in which the two nematode species entered, migrated and caused damage, as well as their development within roots. My observations of roots were made using light microscopy and staining with acid fuchsin. This study showed, in detail, the entry and migration for both nematode species and, for M. javanica, feeding site formation and developmental life stages. This enabled longer time for observations of P. Thornei than was the case with the A. thaliana study. The initial stages of infection were consistent with the Arabidopsis results. However, I was able to observe the later stages of infection, which were markedly different between the two nematode species, although at a lower magnification than in the confocal study. To investigate the effects of the nematode-plant interactions that I had observed in my laboratory studies on plant growth and development, I conducted a pot trial using tomato seedlings, which ran over a period of 11 weeks, using the two previously studied nematode species. Treatments involved inoculation of pots with 5000 larvae. Different pots were infested weekly, from the date of planting to one week before harvest. At harvest (11 weeks), I recorded the length of aerial shoots, the number of green leaves, dry weight of shoots and roots, the combined number of flowers and flower buds and the number, fresh weight and diameter of fruits. M. Javanica significantly (p < 0.05) reduced shoot length, the diameter of the largest fruit, and dry weight of shoots and roots, while P. thornei significantly (p < 0.05) reduced shoot length, number of green leaves, the combined number of flowers and buds, and the dry weight of shoots and roots. While fruit from plants infected with M. javanica had similar moisture content to those in the untreated control, fruit from plants infected with P. thornei had lower moisture content than comparative control plants. These results indicate that the differences between the modes of infection of these two nematode species that I observed in the laboratory studies are manifested in host plant growth and development.Texture, together with pore size and sufficient moisture, is reported to be the primary soil factor influencing plant root-attacking nematode movement towards host roots for infection. I investigated the movement of M. javanica and P. thornei through soils towards the roots of tomato, S. lycopersicum, in a pot trial. For this I used three soils with different textures; namely sand, sandy clay loam and clay. While only a small proportion (< 19% in M. javanica and < 11.5% in P. thornei) of the original inoculum of 300 nematodes were recorded in the tomato roots, this is consistent with previously published studies. However, contrary to previous reports, there were many fewer nematodes present in roots of plants in sandy clay loam soil than in clay soils. The likely explanation is that the sandy clay loam soil had substantially high organic matter, electrical conductivity and silt. This indicates that soil chemistry and, probably, soil biology can play an even more important role than texture in determining nematode movement to and their damage of plant roots. I conclude that M. javanica and P. thornei differ in the way they interact with root tissues during the later stages of infection, although the host cytoskeletal reaction is similar during initial entry by both nematodes. These effects are manifested in the subsequent growth and development of host plants. A combination of soil physical, chemical and biological factors influence the movement of nematodes through soil to roots of host plants, and, in the case of P. thornei, may also influence length of time they spend within roots. The results of my study provide opportunities for further in-depth examination of the infection process, to understand the host-parasite interaction between nematodes and their host plants. A better understanding of the nature of these interactions will assist in formulating improved control strategies for these important nematode pests.

Abstract This chapter provides information on the economic importance, host range, geographical distribution, damage symptoms, biology and life cycle and interactions with other nematodes and pathogens of the root lesion nematode, Pratylenchus thornei, a severe and widespread threat to wheat production in the subtropical grain production region of eastern Australia. Some recommended integrated nematode management practices and future research for nematode resistance breeding are also presented.