Browsing by Author "Eisenback, Jonathan D."

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    Bipolaris zeicola: physiological races, morphology and resistance on maize
    Traut, Eduardo Jorge (Virginia Tech, 1993)
    Conidial length, width, septation, curvature and pigmentation of 39 isolates of Bipolaris zeicola (Stout) Shoemaker from different geographical areas and representing distinct physiological races were examined. Wide variability in conidial morphology was found among isolates of each race. No association was found between races or groups of isolates producing the same shape of lesions and conidial morphology. Morphology and expansion of lesions induced by three races of B. zeicola producing different shapes of lesion on susceptible maize (Zea mays L.) inbred lines were studied. Resistant type lesions induced by three races of B. zeicola were indistinguishable based on their shape or size. However, lesion size correlated with the lesion type induced by each race, indicating that it may be useful to evaluate resistance to different races of B. zeicola. Inheritance of reaction to one isolate of the proposed pathotype of B. zeicola was studied. Resistance was controlled by a single dominant gene in the cross Pr x B37. Forty-nine isolates of B. zeicola from different geographical areas including all the previously described races and pathotype were characterized by their disease reaction, severity and symptoms incited on 14 maize inbred lines. Eleven physiological races were distinguished based on their differential reaction on the 14 inbred lines; however, 6 inbred lines were adequate to differentiate the races. A system based on binary notation is proposed to designate races of B. zeicola on maize. Two races induced typical symptoms of Helminthosporium carbonum-toxin (HC-toxin) production on Pr. Seven races produced oval to irregular lesions on susceptible hosts and did not produce typical lesions of HC-toxin production on Pr. One race induced predominantly long, linear lesions, and another was avirulent on all 14 maize inbred lines.
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    Cellular and Transcriptional Responses of Resistant and Susceptible Cultivars of Alfalfa to the Root Lesion Nematode, Pratylenchus penetrans
    Vieira, Paulo; Mowery, Joseph; Eisenback, Jonathan D.; Shao, Jonathan; Nemchinov, Lev G. (2019-07-31)
    The root lesion nematode (RLN), Pratylenchus penetrans, is a migratory species that attacks a broad range of crops, including alfalfa. High levels of infection can reduce alfalfa forage yields and lead to decreased cold tolerance. Currently, there are no commercially certified varieties with RLN resistance. Little information on molecular interactions between alfalfa and P. penetrans, that would shed light on mechanisms of alfalfa resistance to RLN, is available. To advance our understanding of the host-pathogen interactions and to gain biological insights into the genetics and genomics of host resistance to RLN, we performed a comprehensive assessment of resistant and susceptible interactions of alfalfa with P. penetrans that included root penetration studies, ultrastructural observations, and global gene expression profiling of host plants and the nematode. Several gene-candidates associated with alfalfa resistance to P. penetrans and nematode parasitism genes encoding nematode effector proteins were identified for potential use in alfalfa breeding programs or development of new nematicides. We propose that preformed or constitutive defenses, such as significant accumulation of tannin-like deposits in root cells of the resistant cultivar, could be a key to nematode resistance, at least for the specific case of alfalfa-P. penetrans interaction.
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    Cellular insights of beech leaf disease reveal abnormal ectopic cell division of symptomatic interveinal leaf areas
    Vieira, Paulo; Kantor, Mihail R.; Jansen, Andrew; Handoo, Zafar A.; Eisenback, Jonathan D. (Public Library of Science, 2023-10-05)
    The beech leaf disease nematode, Litylenchus crenatae subsp. mccannii, is recognized as a newly emergent nematode species that causes beech leaf disease (BLD) in beech trees (Fagus spp.) in North America. Changes of leaf morphology before emergence from the bud induced by BLD can provoke dramatic effects on the leaf architecture and consequently to tree performance and development. The initial symptoms of BLD appear as dark green, interveinal banding patterns of the leaf. Despite the fast progression of this disease, the cellular mechanisms leading to the formation of such aberrant leaf phenotype remains totally unknown. To understand the cellular basis of BLD, we employed several types of microscopy to provide an exhaustive characterization of nematode-infected buds and leaves. Histological sections revealed a dramatic cell change composition of these nematode-infected tissues. Diseased bud scale cells were typically hypertrophied and showed a high variability of size. Moreover, while altered cell division had no influence on leaf organogenesis, induction of cell proliferation on young leaf primordia led to a dramatic change in cell layer architecture. Hyperplasia and hypertrophy of the different leaf cell layers, coupled with an abnormal proliferation of chloroplasts especially in the mesophyll cell layers, resulted in the typical interveinal leaf banding. These discrepancies in leaf cell structure were depicted by an abnormal rate of cellular division of the leaf interveinal areas infected by the nematode, promoting significant increase of cell size and leaf thickness. The formation of symptomatic BLD leaves is therefore orchestrated by distinct cellular processes, to enhance the value of these feeding sites and to improve their nutrition status for the nematode. Our findings thus uncover relevant cellular events and provide a structural framework to understand this important disease.
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    Characterization and silencing of the fatty acid- and retinol-binding Pp-far-1 gene in Pratylenchus penetrans
    Vieira, Paulo; Kamo, K.; Eisenback, Jonathan D. (2017-09)
    Fatty acid-and retinol-binding proteins (FARs) are unique to nematodes, and are implicated in a wide range of metabolic and parasitic related functions. Along with the in silico analyses performed in this study, three different FAR members of this family were identified in Pratylenchus penetrans. The cDNA corresponding to the fatty acid-and retinol-binding Pp-far-1 gene was cloned and herein characterized at the molecular level for the first time for this genus. The translated 185 amino acid sequence of P. penetrans FAR-1 sequence, with a predicted molecular weight of 20.82 kDa and a pI of 5.49, shares highest sequence identity to FARs of other migratory nematodes of the Pratylenchidae family (90% to P. vulnus and 80% to Radopholus similis). In situ hybridization localizes Pp-far-1 transcripts in the hypodermis of the nematode. RT-qPCR detected Pp-far-1 transcripts for all nematode developmental stages, with highest expression levels found in juveniles, adult females and adult males, respectively. Pp-far-1 is also highly expressed during infection and establishment of P. penetrans in roots of different host plants, such as corn, lily and soybean. The importance of Pp-far-1 was studied by in planta RNA interference (RNAi) assays using stable soybean hairy root lines. Targeting Pp-far-1 decreased expression of the nematode Pp-far-1 and significantly reduced the reproduction of nematodes, with a total of between 44% and 70% fewer nematodes in comparison to the average number of nematodes counted for control lines. The results indicate that suppressing the expression levels of Pp-far-1 can act as an effective target gene to control P. penetrans.
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    Characterization of Lilium longiflorum cv. 'Nellie White' Infection with Root-lesion Nematode Pratylenchus penetrans by Bright-field and Transmission Electron Microscopy
    Vieira, Paulo; Mowery, Joseph; Kilcrease, James; Eisenback, Jonathan D.; Kamo, Kathryn (2017-03)
    Lilium longiflorum cv. Nellie White, commonly known as Easter lily, is an important floral crop with an annual wholesale value of over $26 million in the United States. The root-lesion nematode, Pratylenchus penetrans, is a major pest of lily due to the significant root damage it causes. In this study, we investigated the cytological aspects of this plant-nematode interaction using bright-field and transmission electron microscopy. We took advantage of an in vitro culture method to multiply lilies and follow the nematode infection over time. Phenotypic reactions of roots inoculated with P. penetrans were evaluated from 0 to 60 d after nematode infection. Symptom development progressed from initial randomly distributed discrete necrotic areas to advanced necrosis along entire roots of each inoculated plant. A major feature characterizing this susceptible host response to nematode infection was the formation of necrosis, browning, and tissue death involving both root epidermis and cortical cells. Degradation of consecutive cell walls resulted in loss of cell pressure, lack of cytoplasmic integrity, followed by cell death along the intracellular path of the nematode's migration. Pratylenchus penetrans was never seen in the vascular cylinder as the layer of collapsed endodermal cells presumably blocked the progression of nematodes into this area of the roots. This study presents the first detailed cytological characterization of P. penetrans infection of Easter lily plants.
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    Cost and Benefit of Seed Treatments and Temik 15G in Furrow for Seedling Disease and Nematode Control in Virginia, 2008
    Phipps, P. M.; Hu, Jiahuai; Eisenback, Jonathan D. (Virginia Cooperative Extension, 2009-11-19)
    Provides details on the 2008 cotton growing season in Virginia. Additionally, provides analysis on the cost and benefits of seedling disease and nematode control through a variety of methods.
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    Description of Longidorus bordonensis sp. nov. from Portugal, with systematics and molecular phylogeny of the genus (Nematoda, Longidoridae)
    Gutierrez-Gutierrez, Carlos; Santos, Margarida Teixeira; Inacio, Maria Lurdes; Eisenback, Jonathan D.; Mota, Manuel (2020-05-05)
    The genus Longidorus currently comprises 176 species of polyphagous plant ectoparasites, including eight species that vector nepo-viruses. Longidorus is one of the most difficult genera to accurately identify species because of the similar morphology and overlapping measurements and ratios among species. Sequences of ribosomal RNA (rRNA)-genes are a powerful level-species diagnostic tool for the genus Longidorus. From 2015 to 2019, a nematode survey was conducted in vineyards and agro-forest environments in Portugal. The populations of Longidorus spp. were characterized through an integrative approach based on morphological data and molecular phylogenetic analysis from rRNA genes (D2-D3 expansion segments of the 28S, ITS1, and partial 18S), including the topotype of L. vinearum. Longidorus bordonensis sp. nov., a didelphic species recovered from the rhizosphere of grasses, is described and illustrated. Longidorus vineacola, with cork oak and wild olive as hosts, is also characterized. This is the first time that L. wicuolea, from cork oak, is reported for Portugal. Bayesian inference (BI) phylogenetic trees for these three molecular markers established phylogenetic relationships among the new species with other Longidorus spp. Phylogenetic trees indicated that i) L. bordonensis sp. nov. is clustered together with other Longidorus spp. and forms a sister clade with L. pini and L. carpetanensis, sharing a short body and odontostyle length, and elongate to conical female tail, and ii) all the other species described and illustrated are phylogenetically associated, including the topotype isolate of L. vinearum.
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    The Effect of Nematode Isolate and Soil Environment on the Tobacco cyst Nematode (Globodera tabacum solanacearum), a Pathogen of Flue-cured Tobacco and Other Solanaceous Crops
    Rideout, Steven L. (Virginia Tech, 1998-12-02)
    Tobacco cyst nematodes (TCN), Globodera tabacum solanacearum, are one of the most serious pests for Virginia flue-cured tobacco (Nicotiana tabacum L.) farmers. These nematodes continue to spread to new farms every year and are now reported in 11 Virginia counties, seven North Carolina counties, and one farm in Maryland. The objectives of this study were to determine the ability of different populations of TCN to reproduce upon both a susceptible (K326) and resistant (NC567) cultivar, to compare TCN reproduction in non-infested soils with currently TCN-infested soils, and to examine reproduction and pathogenicity of TCN on other solanaceous crops. Tobacco cyst nematode reproduction on the TCN-resistant cultivar NC567 was significantly reduced when compared to the TCN-susceptible cultivar K326. Although significant differences among the populations were detected on both cultivars, the differences were not consistent across experiments. Results indicate similar pathogenicity among TCN populations on resistant and susceptible flue-cured tobacco cultivars. Plant breeders may use one population of the tobacco cyst nematode to screen tobacco germplasms for TCN resistance. Significant differences were noted in TCN reproduction among the various soils used in this study. However, the differences were inconsistent, making correlations between TCN reproduction and soil edaphic characteristics unreliable. Sterilizing the soils did not increase TCN reproduction. Reproduction in non-infested soils indicates that TCN will continue to spread throughout tobacco producing regions. Although traditionally an exclusive pest of tobacco, TCN's spread may threaten production of other solanaceous crops. Eggplant (Solanum melongena L.), pepper (Capsicum spp. L.), and tomato (Lycopersicon spp. L.) were confirmed to be hosts of TCN under field conditions. Eggplant was highly susceptible to TCN reproduction and yield suppression, exhibiting a 64% yield reduction in plots not treated with a nematicide compared to fumigated plots. Tomato allowed high rates of TCN reproduction but did not suffer yield loss. Tobacco cyst nematode reproduction was suppressed on pepper compared to the other two crops. No crop loss was noted in nontreated pepper plots compared to plots treated with a nematicide. Results would indicate that tobacco rotations including tomato or eggplant would be unacceptable due to high TCN reproduction rates. The tobacco cyst nematode does not seem to jeopardize the production of tomato and pepper in the southeastern United States, but does threaten profitability of eggplant production in this area.
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    The effect of seaweed concentrate on turfgrass growth, nematode tolerance and protein synthesis under moisture stress conditions
    Sun, Hongwei (Virginia Tech, 1994)
    A preliminary experiment was conducted to determine the effects of salinity and moisture stress on the pathogenicity of root-knot nematodes (RKN) in turfgrass plants. The results indicated that RKN infection adversely affected both visual and functional parameters of bentgrass. Salinity and moisture stress further exaggerated the damage caused by RKN. Under well-watered conditions, the effects of SWC and RKN infection on bentgrass plants were studied. Applications of Swe at 0.5 liter ha⁻¹ and 1.0 liter ha⁻¹ effectively enhanced bentgrass growth under both RKN-free and RKN-infected condition. It was shown that RKN caused less damage to SWC-treated plants than to non-treated plants. In addition, a soil drench of 0.5 liter ha⁻¹ and 1.0 liter ha⁻¹ at 10 day intervals was required to enhance bentgrass growth under RKN-free and RKN-infected conditions, respectively. The effects of seven SWC treatments on the growth of nematode-free and RKN infected bentgrass plants were tested under three irrigation regimes. Rooting and leaf moisture parameters, quality and clipping yield were all improved to some degree by SWC applications. High dosage SWC treatments, applied as a soil drench at one liter ha⁻¹ every 10 days, were most effective in improving plant growth. Application of SWC was more beneficial to RKN-infected plants than RKN-free plants, and to abiotically stressed plants than to abiotic stress-free plants. In a separate study, seaweed application was also shown to enhance both top growth and root growth of lance nematode (Hoplolaimus galeatus) or RKN infected bentgrass grown under drought or salinity stress condition. With SWC application, almost all of the symptoms caused by nematode infection and the abiotic stress were partially overcome. In addition, root development, leaf water status and clipping yield were all improved. It was apparent that soil drench SWC treatments were more effective in enhancing bentgrass growth than foliar Swc treatments. Application of SWC slightly reduced the number of nematodes per unit of fresh root (for RKN) and per unit weight of soil (for lance nematodes). Protein extracted from SWC-treated or non-treated ryegrass plants under different stress conditions indicated that SWC altered plant protein synthesis, possibly by inducing selective gene expressions.
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    Effects of topping, stem density, and stage of vine cutting on canopy growth and tuber yield yield of potato (Solanum tuberosum L.)
    Okeyo, James Ajuoga (Virginia Tech, 1995)
    Seed tubers of ‘Yukon Gold’ potato (Solanum tuberosum L.) exhibit strong apical dominance, resulting in low stem density after planting. After emergence, the terminal buds reimpose apical dominance on the rest of the canopy leading to production of few secondary branches. Therefore, several experiments were conducted at the Virginia Polytechnic Institute and State University Kentland Research Farm, Blacksburg in 1992, 1993, and 1994 to evaluate the effects of topping [(excising 2-3 cm from the terminal buds at 1 to 2 weeks after the date of plant emergence (WAE)], stage of vine cutting at ground level, and main stem density on canopy growth, tuber bulking rate, and tuber yields of potato. Topping (3 years) and vine cutting (2 years) at 1 WAE resulted in more uniform plant stands and increased average yield of US No. 1 tubers of ‘Yukon Gold’ by 16 and 14%, compared to untopped and uncut plants, respectively. When plants of ‘Kennebec’, ’Superior’, and ’Yukon Gold’ were topped in 1994, yield of US No. 1 tubers increased by an average of 10%, indicating that topping could be used to improve tuber yield of potato cultivars exhibiting different growth habits. The increased tuber yields following topping resulted from a combination of increased leaf area duration and increased period of tuber bulking. Cutting vines of ‘Yukon Gold’ at 2, 4, and 6 WAE in 1992 and 1993, decreased yield of US No. 1 tubers by 11, 69, and 38% and by 19, 56, and 48%, respectively. Yield of US No. 1 tubers increased with increased stem density and increased in-row spacing. Interaction effects between in row spacing and topping were significant. Control plants of ’Yukon Gold’ produced higher tuber bulking rates and yield of US No. 1 tubers than topped plants at 15 cm in-row spacing, while topped plants had higher tuber bulking rates and yield of US No. 1 tubers than control plants at 20, 25, and 30 cm in-row spacings. Neither topping nor in-row spacing increased the incidence of hollow heart of tubers in 1994. The results showed that the difference in tuber yield between topped and control plants was greater during long growing season and topped plants should be spaced at 25 cm in-row in order to obtain maximum tuber yield.
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    Evaluation of Anion Transporters as Potential Target Sites for Insect and Nematode Control: Toxicological, Electrophysiological, and Molecular Studies
    Boina, Dhana Raj (Virginia Tech, 2008-01-03)
    In this study, four anion transporter (AT) blockers, DIDS (4, 4′-diisothiocyanatostilbene-2, 2′-disulfonic acid), 9-AC (anthracene-9-carboxylic acid), NPPB (5-nitro-2-(3-phenylpropylamino) benzoic acid), and IAA-94 (indanyloxy acetic acid) were selected to evaluate ATs as potential target sites for insect and nematode control. All the AT blockers showed slowly developing toxicity against second-stage larvae of Meloidogyne incognita (Kofoid and White 1919) Chitwood 1949 and adults of Caenorhabditis elegans Maupas 1900 but not against third-stage larvae of Heterorhabditis bacteriophora Poinar 1975 even at 200 ppm. Symptoms of AT blocker toxicity observed in C. elegans adults were increased pharyngeal muscle contractions and decreased locomotion. Exposure of C. elegans as fourth-stage larvae to double-stranded RNA (dsRNA) of ceclc-1 and ceclc-2 (VGCC genes coding for CeClC-1 and CeClC-2, respectively) either alone or together for 24 h decreased their expression in F1 progeny in a time-dependent manner. Reduction in expression of ceclc-2 alone or together with ceclc-1 significantly increased pharyngeal contractions and decreased locomotion in significantly higher percentage of F1 progeny. The above findings suggested AT blockers nematicidal activity primarily comes from inhibition of CeClC-2 channels, while inhibition of CeClC-1 channels may enhance this activity. All the AT blockers showed slowly developing toxicity against adults of a susceptible strain (Oregon-R) of Drosophila melanogaster Meigen 1830, while DIDS, was equally toxic to dieldrin-resistant rdl flies. All AT blockers, except 9-AC, at 100 µM showed significant excitatory effect on desheathed central nervous system (CNS) of third-instar larvae of Drosophila, while DIDS showed a modest excitatory effect on ascending peripheral nerves. Feeding adult flies on 10% sugar solution mixed with 100 ppm of DIDS for 6 h decreased the midgut pH by 2 units approximately. All the AT blockers inhibited the growth of larvae (in weight), increased the developmental time, and decreased survival when Ostrinia nubilalis (Hübner 1796) second-instar larvae were fed for seven days. All the AT blockers decreased the midgut alkalinity and inhibited chloride ion transport from midgut lumen into epithelia in fifth-instar larvae when fed for 3 h on treated diet. Positive correlations observed among growth, midgut alkalinity, and midgut chloride transport in AT blocker-fed larvae suggested that inhibition of chloride/bicarbonate exchangers by AT blockers may have contributed to midgut alkalinity decrease affecting the digestion and resulting in observed lethal and sublethal effects.
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    Expanding the RNA virome of nematodes and other soil-inhabiting organisms
    Vieira, Paulo; Subbotin, Sergei A.; Alkharouf, Nadim; Eisenback, Jonathan D.; Nemchinov, Lev G. (Oxford University Press, 2022-03-30)
    In recent years, several newly discovered viruses infecting free-living nematodes, sedentary plant-parasitic nematodes, and migratory root lesion nematodes have been described. However, to the best of our knowledge, no comprehensive research focusing exclusively on metagenomic analysis of the soil nematode community virome has thus far been carried out. In this work, we have attempted to bridge this gap by investigating viral communities that are associated with soil-inhabiting organisms, particularly nematodes. This study demonstrates a remarkable diversity of RNA viruses in the natural soil environment. Over 150 viruses were identified in different soil-inhabiting hosts, of which more than 139 are potentially new virus species. Many of these viruses belong to the nematode virome, thereby enriching our understanding of the diversity and evolution of this complex part of the natural ecosystem.
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    First Insights into the Genetic Diversity of the Pinewood Nematode in Its Native Area Using New Polymorphic Microsatellite Loci
    Mallez, Sophie; Castagnone, Chantal; Espada, Margarida; Vieira, Paulo; Eisenback, Jonathan D.; Mota, Manuel; Guillemaud, Thomas; Castagnone-Sereno, Philippe (PLOS, 2013-03-15)
    The pinewood nematode, Bursaphelenchus xylophilus, native to North America, is the causative agent of pine wilt disease and among the most important invasive forest pests in the East-Asian countries, such as Japan and China. Since 1999, it has been found in Europe in the Iberian Peninsula, where it also causes significant damage. In a previous study, 94 pairs of microsatellite primers have been identified in silico in the pinewood nematode genome. In the present study, specific PCR amplifications and polymorphism tests to validate these loci were performed and 17 microsatellite loci that were suitable for routine analysis of B. xylophilus genetic diversity were selected. The polymorphism of these markers was evaluated on nematodes from four field origins and one laboratory collection strain, all originate from the native area. The number of alleles and the expected heterozygosity varied between 2 and 11 and between 0.039 and 0.777, respectively. First insights into the population genetic structure of B. xylophilus were obtained using clustering and multivariate methods on the genotypes obtained from the field samples. The results showed that the pinewood nematode genetic diversity is spatially structured at the scale of the pine tree and probably at larger scales. The role of dispersal by the insect vector versus human activities in shaping this structure is discussed.
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    Identification and characterization of the first pectin methylesterase gene discovered in the root lesion nematode Pratylenchus penetrans
    Vicente, Cláudia S. L.; Nemchinov, Lev G.; Mota, Manuel; Eisenback, Jonathan D.; Kamo, Kathryn; Vieira, Paulo (Public Library of Science, 2019-02-22)
    Similar to other plant-parasitic nematodes, root lesion nematodes possess an array of enzymes that are involved in the degradation of the plant cell wall. Here we report the identification of a gene encoding a cell wall-degrading enzyme, pectin methylesterase PME (EC 3.1.1.11), in the root lesion nematode Pratylenchus penetrans. Both genomic and coding sequences of the gene were cloned for this species, that included the presence of four introns which eliminated a possible contamination from bacteria. Expression of the Pp-pme gene was localized in the esophageal glands of P. penetrans as determined by in situ hybridization. Temporal expression of Pp-pme in planta was validated at early time points of infection. The possible function and activity of the gene were assessed by transient expression of Pp-pme in plants of Nicotiana benthamiana plants via a Potato virus X-based vector. To our knowledge, this is the first report on identification and characterization of a PME gene within the phylum Nematoda. This is an open access article, free of all copyright, and may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose. The work is made available under the Creative Commons CC0 public domain dedication.
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    Identification and genetic characterization of tobacco accessions possessing resistance to tobacco cyst nematode
    Hayes, Alec J. (Virginia Tech, 1995-05-05)
    Developing a flue-cured tobacco cultivar with high resistance to tobacco cyst nematode (TCN) is an important initiative in the Southern Piedmont of Virginia, where this pathogen causes severe yield losses. One hundred twenty eight lines representing a diverse geographic array of tobacco accessions, including cultivars from several types of tobacco, flue-cured-type tobacco introductions, and wild Nicotiana species were evaluated for TCN resistance under greenhouse conditions. Inheritance of TCN resistance has been reported to be closely linked or pleiotropic to inheritance of wildfire resistance. Consequently, accessions were also screened for wildfire resistance under greenhouse conditions to evaluate this relationship among a diverse group of tobacco accessions. Twenty-one accessions were identified with resistance to TCN. Response to the two pathogens was highly correlated. However, there was no relationship between resistance to the two pathogens for several accessions. 'KY 190', a fire-cured cultivar, possessed the N. longiflora source of wildfire resistance, but was found susceptible to TCN. This result seems to rule out pleiotropy and is consistent with the assertion that the two resistance genes are closely linked. six TCN resistant lines and two susceptible lines were selected and a diallel study was conducted to determine the inheritance of resistance to TCN. Additive gene action contributed significantly to inheritance of TCN resistance. Three accessions, 'Burley 64', 'Kutsaga 110', and 'Tl 1597', were determined to be the most promising parents for use in a breeding program designed to develop a flue-cured cultivar with a high level of TCN resistance.
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    Impact of Cotton Monoculture, Variety Selection, and Chemical Inputs on Disease Control, 2011
    Phipps, P. M.; Telenko, D. E. P.; Eisenback, Jonathan D. (Virginia Cooperative Extension, 2012-01-27)
    Provides information on the 2011 cotton growing season in Virginia, including discussion of seedling disease and nematode losses, national cotton seed treatment trial, response of low vigor and high vigor seed to seed treatments, and results from several different field based experimental trials.
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    Induced disease resistance elicited by acibenzolar-S-methyl and plant growth-promoting rhizobacteria in tobacco (Nicotiana tabacum L.)
    Parkunan, Venkatesan (Virginia Tech, 2008-09-15)
    Active disease resistance in plants is induced during the pathogen infection process that triggers multiple defense-related genes to establish broad-spectrum resistance. Several biotic and abiotic agents can mimic natural induced resistance (IR), categorized as systemic acquired (SAR) or induced systemic resistance (ISR). IR, triggered by acibenzolar-S-methyl (ASM) or plant growth-promoting rhizobacteria (PGPR), was evaluated on two-to-three types of tobacco in greenhouse and field studies. Tobacco mosaic virus (TMV) local lesion assays monitored induction and maintenance of ASM-induced SAR over a 21 day period via proportional reduction in the number of TMV local lesions between an untreated control and ASM-treated plants. Intraspecific variation in SAR was found among tobacco types; burley and flue-cured tobaccos responded by day 3, while oriental tobacco responded between day 3 and 6. The SAR signal was greatest between 6 and 15 days following ASM application, but IR was slightly evident even at 21 days after ASM application in all three tobacco types. Bottom and middle leaves responded similarly on all sample dates, but top leaves showed the weakest SAR response. Tobacco cyst nematode (TCN; Globodera tabacum solanacearum) is one of the most destructive pathogens of tobacco in Virginia. Among four PGPR combinations tested, a mixture of Bacillus amyloliquefaciens IN937a (GB99) and B. subtilis A13 (GB122) most consistently suppressed TCN reproduction in flue-cured and oriental tobacco. Application of ASM similarly reduced final numbers of TCN cysts, but also resulted in chlorosis, stunting, and lower plant fresh weight. GB99+GB122 also suppressed TCN development and reproduction in susceptible and resistant flue-cured cultivars, but reductions by ASM were less consistent. In a split-root trial, soil amendment with GB99+GB122 in one half of an oriental tobacco root system lowered final numbers of TCN more than did ASM. ASM exhibited undesirable effects in phytotoxicity trials in flue-cured and oriental tobacco, but GB99+GB122 was not phytotoxic. When oriental tobacco seedlings were grown in a GB99+GB122-treated soil-less media, a single application of 200 mg ASM/L one week after transplanting significantly suppressed TCN reproduction in the field without phytotoxicity. Further field research is needed to confirm this effect in flue-cured tobacco.
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    Inheritance of Resistance to Tobacco Cyst Nematode Globodera tabacum solanacearum
    Crowder, Barbara Jean (Virginia Tech, 2000-11-27)
    The tobacco cyst nematode [Globodera tabacum solanacearum (Miller & Gray, 1972) Behrens, 1975] is an important pathogen affecting flue-cured tobacco (Nicotiana tabacum L.) in Virginia, North Carolina, and Maryland. The resistant cultivars Coker 371 Gold and Kutsaga 110 were evaluated during 1999 and 2000 in the greenhouse to determine the mode of inheritance of resistance to the tobacco cyst nematode (TCN). Each cultivar was crossed to the susceptible cultivar K 326 and F1 progeny were backcrossed to each parent. Plants from each parent and F1, F2, BC1Ps, and BC1Pr progeny were evaluated for TCN resistance. Six-week-old transplants were inoculated with 6000 TCN eggs from crushed cysts. Eight weeks after inoculation, a 1-g sample of fibrous root was stained and vermiform, swollen, pyriform, and adult nematodes were counted. The number of cysts and eggs per 400 cm3 of soil were counted from each transplant. Generation means analyses were performed. Additive and dominance gene action play an important role in resistance to TCN in Coker 371 Gold and Kutsaga 110. F2 generation data from the Coker 371 Gold cross fit a 3:1 (resistant:susceptible) segregation ratio and BC1Ps generation data fit a 1:1 segregation ratio, indicating that resistance to TCN is conferred by a single dominant gene. A continuous range of variation was observed among the F2 progeny for the K 326 X Kutsaga 110 cross, indicating resistance in Kutsaga 110 is quantitative. TCN resistance in Coker 371 Gold and Kutsaga 110 may be derived from different sources.
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    Intraspecific Variability within Globodera tabacum solanacearum and Selection for Virulence Against Flue-Cured Tobacco
    Syracuse, Aaron James (Virginia Tech, 2002-10-14)
    The tobacco cyst nematode (TCN), Globodera tabacum solanacearum [(Miller and Gray, 1972) Behrens 1975] Stone 1983, is one of the most economically important pests of flue-cured tobacco (Nicotiana tabacum L.) in Virginia. Although TCN has been reported from other countries, the geographical distribution of G. t. solanacearum within the United States is limited to Virginia, North Carolina, and one county in Maryland. Approximately 30% of the tobacco acreage in Virginia is infested; average yield reduction is 15%, but complete crop failure can occur. The objectives of this research were to examine intraspecific variability within G. t. solanacearum and to evaluate the relative adaptability of G. t. solanacearum on a resistant (NC567) and a susceptible (K326) flue-cured tobacco cultivar. Nineteen geographic isolates of G. t. solanacearum, one isolate each of G. t. virginiae and the Mexican cyst nematode (G. "mexicana"), two isolates of G. t. tabacum, and five Heterodera species were characterized by DNA fingerprinting using the RAPD-PCR technique. Reproducible differences in fragment patterns allowed similar differentiation of the isolates and species with each primer. Hierarchical cluster analysis was performed to illustrate the relatedness between nematode isolates and species. In contrast to reports in the literature, we found a Miller isolate of G. "mexicana" to cluster more closely with G. t. solanacearum than with G. t. tabacum or G. t. virginiae. Although no pathotype differences have been found within G. t. solanacearum, the average Jaccard's similarity index among isolates of G. t. solanacearum was 74%, representing greater variation than that observed across different pathotypes of the closely related potato cyst nematode, Globodera pallida. This result suggests that the emergence of resistance-breaking biotypes is more likely than previous research suggests. If a new pathotype is reported, a RAPD marker associated with virulence against a specific host resistance gene could prove to be a valuable tool in population diagnosis, resistance screening, and overall TCN management. One isolate of G. t. solanacearum was cultured on a resistant (NC567) and a susceptible (K326) flue-cured tobacco cultivar over five generations. Variable TCN reproduction was observed on both cultivars over each generation. This variability in reproduction could be attributed to differences among generations in the time interval between inoculation and cyst extraction, temperature, possible diapause effects, and/or daylength. Ninety-eight cysts were produced in the fifth and final generation compared to the 14 to 50 cysts produced during each of the previous four generations. Increased reproduction on the resistant variety suggests that increased virulence might be selected, but research involving additional generations would need to be carried out in order to conclude whether or not TCN virulence is being selected.
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    Life Cycle of the root-knot nematode (3rd printing)
    Eisenback, Jonathan D. (Society of Nematologists Education Committee, 2023-06-30)
    Educational poster.