Browsing by Author "Tolin, Sue A."
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- Analysis of anther-derived plants of Solanum phureja: variation in ploidy, photosynthetic efficiency and structure of the nuclear genomePehu, Eija (Virginia Polytechnic Institute and State University, 1986)The ultimate goal of the· breeding scheme, of which the present study is a part, is to introduce exotic germplasm into existing cultivars of Solanum tuberosum through· 4x X 2x crosses using the South American diploid potato species Solanum phureja as the pollen parent. The first phase of this program includes the 'reconstruction' of a highly heterozygous diploid, pollen parent by .first : reducing the chromosome number of the S. phureja clones to the monoploid level and subsequently fusing genomes of two unrelated monoploid plants either by somatic hybridization or by cross-pollination between fertile doubled monoploids. Within this framework, the objectives of this research were to analyze variation among anther-derived plants of Solanum phureja regarding their: 1) ploidy level and morphology, 2) net photosynthesis and its biochemical components, and 3) nuclear genomic structure, particularly with regard ·to the amplification of rRNA genes as influenced by the anther-culture process. Based on the analysis of several morphological characters of the anther-derived plants by canonical discriminant function, four characters (anther length, number of chloroplasts/pair of guard cells, leaf width, corolla width) were selected for most effective assignment of plants to their ploidy groups by clustering procedures. Clustering of the anther-derived plants proved to be an efficient means of separating monoploids from higher ploidy levels. To assess the impact of the process of anther-culture on the physiology of the resulting plants and to evaluate the possibility of selecting anther-derived genotypes for further breeding efforts, monoploid, diploid and tetraploid anther-derived plants were studied regarding their net photosynthesis and its component characteristics. Leaf area, net photosynthesis and chlorophyll content increased with increasing ploidy' Among .the. monoploids I. Rubisco activity and concentration displayed a. significant genotypic effect; whereas in the diploid group variation among genotypes was significant for total protein content and maximum specific activity of ribulose bisphosphate carboxylase. Among the tetraploid genotypes, significant differenc.es were found with respect to net photosynthesis and specific leaf weight. Two exceptional genotypes were identified: a monoploid with an increase of 28% fcfr maximum activity of ribulose bisphosphate carboxylase and a tetraploid with an increase of 30% for net photosynthesis over the anther-donor plant. To evaluate DNA variation among the anther-derived plants, the nuclear genomes of anther-derived monoploid and diploid plant were studied by DNA reassociation kinetics. It was found that the nuclear genome of the monoploid has undergone differential replication resulting in an increase of sequences consisting of highly· repetitive DNA. Free solution RNA-DNA hybridization showed that the monoploid DNA contained 30% more rDNA sequences than the diploid. Southern blot analysis using rRNA as the probe revealed variation for copy number of certain restriction fragments and for restriction enzyme cleavage sites.
- Analysis of factors that affect parvovirus expressionBraddon, Virginia Rendall (Virginia Tech, 1994-05-05)The positions of sequences necessary for transcription from the promoter located at map unit 4 of the bovine parvovirus (BPV) genome were determined. The autonomous parvoviruses, of which BPV is a member, contain two transcriptional units with promoters active in temporal order during infection. BPV proteins also appear in the same temporal order; the nonstructural (NS) proteins are produced before the capsid proteins. Northern blot analysis of BPV RNAs suggest that, like human parvovirus B19, all transcripts of BPV are initiated from a single promoter. A reporter construct was created by cloning the sequences from BPV containing the TAT A box located at nucleotides (nt) 250 - 254 upstream of the luciferase gene. A series of mutants were generated by deletion of restriction endonuclease fragments. Expression was assayed by transient expression of the constructs in transfected bovine fetal lung (BFL) cells, derived from the natural host. The data indicates that expression can be directed from the sequences containing the TAT A box. Analysis of expression of the deletion clones show that sequences from nt 120 - 170 of the BPV genome are also required for transcription. A search of these sequences reveals at least two consensus binding sites for cellular transcription factors. These are AP-I and the major late transcription factor (MLTF). MLTF has been shown to induce transcription from the early promoter of the dependovirus adena-associated virus (AA V). The presence of viral proteins provided in trans decreases expression from all constructs, with one exception. Expression, when nt 0 - 50 are deleted, is increased in the presence of mutant BPV NS-I. Feedback inhibition of P4 expression by NS-I, the P4 gene product, is seen in H-l, a rat parvovirus. The expression of BPV proteins in synchronized HeLa cells, which are not a natural tissue culture host was examined to determine the effect of a non-permissive host on BPV transcription. Expression of viral proteins in some parvoviruses is blocked in non-permissive cells. A block in transcription is seen during infection of non-permissive cells by B 19. AA V P5 expression is negatively regulated without co-infection of a helper virus, a non-permissive state. Luciferase activity was 570/0, compared to BFL cells. and a similar decrease in expression in the presence of viral proteins was observed. Viral nonstructural and capsid proteins could be detected by immunofluorescence, but only in the cytoplasm, suggesting that expression of viral proteins necessary for replication was not the block to a productive infection, but rather their translocation to the nucleus, as seen during restrictive H-l infection of transformed cells. BPV proteins have been observed localized to nuclear foci of transfected, synchronized BFL cells. The subcellular localization of viral proteins was detected by indirect immunofluorescence labeling using antiserum that recognizes both nonstructural and capsid proteins. Punctate nuclear staining has not been observed routinely during BPV infection or transfection of actively dividing cells. AA V proteins expressed in either BFL and HeLa cells, synchronized by hydroxyurea, were also observed in distinct nuclear foci. The same pattern of localization has been observed during co-infection of cells with AA V and adeno-virus, and during H-I infection. Gel mobility shift assays show that a cellular protein from BFL cells synchronized in S-phase recognizes and binds the right terminus of BPV. The right terminus, in hairpin and double-stranded linear forms, is an effective competitor, indicating the complex is specific, and suggesting that sequence, rather than structure may be the recognition signal for this cellular protein. The left terminus of BPV, in the hairpin conformation is also an efficient competitor for complex formation. It has been shown that a cellular protein forms a complex with the left terminus and that the right terminus is an efficient competitor for complex formation. This data taken together suggests the same cellular factor may recognize both termini, and correlates with the observation that both can act as origins of replication, and could be recognized by similar proteins. The heterologous terminus of AAV in the hairpin conformation, is not an efficient competitor for complex formation between the right terminus of BPV and a BFL cell protein. The lack of competition may support the indication that the recognition signal is a specific sequence rather than a particular secondary structure.
- Application of Spatial Analysis in the Incidence of the Gall Midge in Jamaican Hot Pepper ProductionWilliams, Ryan Williams (Virginia Tech, 2001-05-30)Jamaican farmers are experiencing constraints to hot pepper (Capsicum chinense) export production due to a quarantine pest -- the gall midge (Contarinia lycopersici; Prodiplosis longifila). There is a threat of gall midge introduction into the United States, where the insect pest is not known to occur. This research tests the significance of a range of variables to gall midge incidence. The purpose was to explain the spatial patterns that result from the relationships between gall midge incidence in hot pepper production and production methods and/or environmental conditions. There were three components to the sample of 47 farm visits: the interview, the hot pepper sampling, and the measurements of physical and locational attributes. Producers responded to questions about production methods, marketing, and quarantine issues. The percent of infested fruits per plot was calculated. GPS was used to record farm location. Using ArcView, environmental and climatic datasets were overlaid with farm locations and their attributes. Multiple regression was used to measure significance of variables to gall midge incidence. Cluster analyses were used to demonstrate the spatial patterns of the variability of gall midge incidence and its associated variables. There was significant effect on incidence by farm elevation, observance of pesticide-use recommendations, producer awareness of pre-clearance fumigation, and the use of intercropping in hot pepper production.
- Arguing the Genome: A Topology of the Argumentation Behind the Construction of the Human Genome ProjectAllender-Hagedorn, Susan (Virginia Tech, 2001-04-10)The Human Genome Project (HGP), the name given to the scientific program to map and decode all of human genetic material, has been projected to revolutionize the conduct of biological science in the twenty-first century. For several years before its formation in 1990, a federally-funded, systematic study of the human genome was discussed first in the scientific arena and then in the public arena. The central thesis of this dissertation is that the arguments supporting or rejecting creation of the HGP and the rhetorical devices used to further those arguments had a major influence on the shape the HGP took in 1991. The argumentation used both for and against the creation of the HGP before the public as well as on the border between the public and scientific arenas is studied. The rhetorical devices such as metaphor, narrative, and selective word choices used to further these arguments are also examined. In particular, a rhetorical content analysis was performed on the 1986-1991 argumentation available to the most crucial audience for such persuasion: the members of Congress who ultimately voted for or against the program's funding and its establishment as a part of U.S. science policy. The proponents of the HGP, especially after the first year of public debate, presented their arguments in a wider arena of discussion and presented more and more varied arguments to advocate the project. The opposition raised questions that had for the most part been answered earlier in the debate. Often anti-HGP arguments focused on less effective audiences (scientists instead of members of Congress). Opposition to the project didn't become organized until near the end of the time frame studied, too late to have much of an impact on the outcome of the debate. The rhetorical devices studied served to magnify the impact of arguments used: in particular, the metaphor served as a boundary object to bridge discussions between the scientific and the public arenas. Ultimately the victory in the debate over the establishment of the HGP was awarded to the promulgators of the strongest underlying metaphor--the idealized excitement and profit of exploration of unknown territory--and the benefits to come from filling in and conquering the unknown areas of the human genetic map, territory the U.S. was eager to claim for its own.
- Assessing the Distribution and Impact of Bean pod mottle virus (BPMV) as a Re-emerging Virus, and Soybean mosaic virus (SMV) in Soybean Grown in VirginiaMackasmiel, Lucas A. (Virginia Tech, 2004-07-12)Bean pod mottle virus (BPMV, Genus Comovirus, Family: Comoviridae)is an important virus in soybean (Glycine max (L.) Merrill), causing quality and yield loss due to seed coat mottling and seed weight reduction. Although BPMV has been known in Virginia since 1958 and has always been regarded as causing negligible losses, its impact is changing as BPMV incidence has increased in many soybean growing areas of Virginia and the USA in general. From 1997 to 2001, a total of five BPMV isolates (V-W1, V-W2, V-S98-1, V-S98-15 and V-S01-10) were collected in Virginia and characterized. In this study, the effects of these isolates were studied, alone or with Soybean mosaic virus (SMV, Genus Potyvirus, Family Potyviridae) strain SMV G1, and isolates S98-51 and S98-52, on selected soybean cultivars. Individual isolates of BPMV showed variable symptom severity, and resulted in yield loss of between 40.4 to 58.1%, while SMV caused 23.7% in the most severe interactions. Up to 100% yield loss was realized from double inoculations of selected BPMV and SMV isolates, BPMV V-S98-1 + SMV S98-52 and BPMV S98-15 + SMV S98-52 on Hutcheson and Hutcheson Roundup Ready® (BC5) soybeans, respectively. Time of inoculation, a critical factor in the impact of many virus diseases, affected seed coat mottling in four cultivars and seed weight in two cultivars, in tests with four BPMV isolates and three stages of soybean development. All BPMV isolates inoculated to plants at vegetative stage V1-V3 severely increased seed coat mottling and reduced seed weight than those inoculated at V4-V6 and reproductive stage R1-R3. Seedlings grown from non-mottled seeds germinated more uniformly had fewer thin-stemmed seedlings and grew faster than those grown from mottled seeds. Inoculation of various cultivars and breeding lines showed that there was no correlation between the severity of virus-induced foliar symptoms, relative accumulation of SMV, and extent of seed coat mottling. Thus, by avoiding the presence of BPMV at an early growth stage through proper timing of planting to avoid vectors, proper cultural practices like weed control, use of SMV free seeds, and chemical control, it is possible to greatly improve seed quality and reduce yield losses in soybean.
- Bean Leaf Beetle: Impact of Leaf Feeding Injury on Snap Beans, Host Plant Choice and Role as a Vector of Bean Pod Mottle Virus in VirginiaCassell, Meredith Edana (Virginia Tech, 2011-04-12)The bean leaf beetle (BLB), Cerotoma trifurcata (Forster) (Coleoptera: Chrysomelidae), is a pest of commercially produced legumes in eastern Virginia. Field cage and manual-defoliation studies were conducted in Virginia to determine an economic impact of BLB. In the manual-defoliation study, snap bean plants had significant yield loss when > 25% of leaf area was removed. In the field cage experiments, I was unable to establish beetle densities per plant to impact yield. Host plant selection by BLB was done in laboratory and field studies with snap bean, lima bean, and soybeans. Laboratory studies showed that BLB preferred snap bean and lima bean over soybean. Field studies did not showed no preference. A survey was conducted on the Eastern Shore of Virginia determine the epicenter of BPMV. Soybean leaves and beetles were collected and assessed for BPMV by ELISA or TBIA. Beetles at the ESAREC were BPMV-positive upon emergence from overwintering sites, but the virus load was low when tested by ELISA. This suggests acquisition of virus from a source other than infected cultivated legumes. To find the potential inoculum sources of BPMV in eastern Virginia, leguminous weeds and perennial weeds were tested for BPMV. Four weed species gave BPMV-positive tissue blots including: Oxalis stricta, Rumex acetosella, Trifolium pretense, and Trifolium repens. Insecticidal seed treatment of thiamethoxam on soybean seeds was evaluated to test the efficacy. Leaf area eaten and beetle mortality was measured. The thiamethoxam seed treatment protected soybean seedlings from beetle feeding through the V2 stage of growth.
- Bean Pod Mottle Virus in Virginia SoybeansCassell, Meredith E.; Tolin, Sue A.; Kuhar, Thomas P.; Schultz, Peter B. (Virginia Cooperative Extension, 2009-10-09)Describes disease cycle of Bean Pod Mottle Virus in soybeans. Also describes symptoms, possible sources of this disease, and management methods.
- Bovine parvovirus and bovine enterovirus in mixed infectionsDorsey, Ralph Benjamin (Virginia Tech, 1975-08-15)Bovine fetal spleen cells synchronized with 2mM hydroxyurea were infected with bovine parvovirus and bovine enterovirus in order to study the events occurring when DNA and RNA viruses mixedly infect single cells. The objectives of this research were threefold. First, to determine the effects of single infection of synchronized bovine fetal spleen cells by bovine parvovirus and bovine enterovirus on cellular macromolecular syntheses. Second, to study the effect of simultaneous infection of synchronized cells by bovine parvovirus and bovine enterovirus. Third, to investigate the interactions which occur when synchronized cells are pre-infected with bovine parvovirus and superinfected with bovine enterovirus. Single infection of cells with bovine parvovirus upon release from hydroxyurea does not affect cellular macromolecular syntheses until 8 hr after infection; whereas, single infection with bovine enterovirus results in a rapid decrease in the rates of total DNA, RNA, and protein synthesis by 2 hr after infection. In simultaneously infected cells, the enterovirus replication is not inhibited while the level of parvovirus is severely reduced. However, in cells pre-infected with bovine parvovirus and super-infected with bovine enterovirus, the replication of both viruses is dramatically decreased. It can be seen from the results obtained in the study of two protocols of mixed infection, that many different virus-host interactions and virus-virus interactions can occur in a mixed infection. The time sequence of infection of the two viruses determines what interactions take place.
- Candidate Gene Sequence Analyses toward Identifying Rsv3-Type Resistance to Soybean Mosaic VirusRedekar, Neelam R.; Clevinger, Elizabeth M.; Laskar, M. A.; Biyashev, Ruslan M.; Ashfield, Tom; Jensen, Roderick V.; Jeong, Soon-Chun; Tolin, Sue A.; Saghai-Maroof, Mohammad A. (Crop Science Society of America, 2016-05-13)Rsv3 is one of three genetic loci conferring strain-specific resistance to Soybean mosaic virus (SMV). The Rsv3 locus has been mapped to a 154-kb region on chromosome 14, containing a cluster of five nucleotide-binding leucine-rich repeat (NB-LRR) resistance genes. High sequence similarity between the Rsv3 candidate genes challenges fine mapping of the locus. Among the five, Glyma14g38533 showed the highest transcript abundance in 1 to 3 h of SMV-G7 inoculation. Comparative sequence analyses were conducted with the five Rsv3 candidate NB-LRR genes from susceptible (rsv-type) soybean [Glycine max (L.) Merr.] cultivar Williams 82, resistant (Rsv3-type) cultivar Hwangkeum, and resistant lines L29 and RRR. Sequence comparisons revealed that Glyma14g38533 had far more polymorphisms than the other candidate genes. Interestingly, Glyma14g38533 gene from Rsv3-type lines exhibited 150 single-nucleotide polymorphism (SNP and six insertion–deletion (InDel) markers relative to rsv-type line, Furthermore, the polymorphisms identified in three Rsv3-type lines were highly conserved. Several polymorphisms were validated in 18 Rsv3-type resistant and six rsv-type susceptible lines and were found associated with their disease response. The majority of the polymorphisms were located in LRR domain encoding region, which is involved in pathogen recognition via protein–protein interactions. These findings associating Glyma14g38533 with Rsv3-type resistance to SMV suggest it is the most likely candidate gene for Rsv3.
- Cellular factors and viral elements for parvovirus replicationDeville, Catherine Michele (Virginia Tech, 1994-04-15)Autonomous parvoviruses, such as bovine parvovirus (BPV), need a factor present at the S-phase of the cell cycle for a productive infection, while dependent parvoviruses, the adenoassociated viruses (AAVs), require a helper virus to complete an infectious cycle. However, AAV can replicate autonomously in synchronized cells, suggesting that an S-phase factor substitutes for the helper virus. To investigate the nature of the cellular S-phase factor, we performed DNA retardation assays with uninfected nuclear extracts of S-phase cells, synchronized by hydroxyurea pretreatment, and radiolabeled parvoviral termini in their hairpinned conformation. We observed that proteins in HeLa cells, a tissue culture host for AAV, specifically interacted with the terminal sequences of this virus, which act as origins of replication (oris). These assays also showed specific binding between S-phase cellular proteins and termini (oris) of heterologous parvoviruses, for which the cells are not a natural host. For example, proteins from bovine fetal lung (BFL) cells, a tissue culture host for BPV, were able to bind to an AAV terminus and HeLa cell proteins interacted with both termini of the BPV genome. All DNA-protein complexes investigated appeared to be specific for S-phase synchronized cells. In order to begin to characterize the protein(s) involved in the complex formation, we performed SDS-PAGE electrophoresis of some retarded complexes. We report that a 54 kd protein was contained in the complex formed with the BPV left terminus and BFL cell extract. [Binding of BFL cell proteins to a BPV left terminus has been reported earlier]. Using a similar technique, we observed that two phosphoproteins of 55 and 90 kd were present in the retarded complex formed between a BPV left terminus and HeLa cell extract. An antibody directed against human p53, an anti-oncoprotein, was shown to compete binding of BFL cell extract and HeLa cell extract to the BPV left terminus. This antibody also competed the binding of HeLa cell extract to the AAV terminus. Our data suggest that proteins with similar characteristics, most probably among which is p53, are involved in the ori-binding complexes, possibly exerting a role as positive regulator of parvoviral replication. The secondary structure of the viral ends is remarkably conserved among parvoviruses. Of particular interest is the presence of mismatched/unpaired nucleotides, forming a bubble, in the stem of the left hairpin of almost all autonomous parvoviruses. To analyze the possible role of these unpaired/mismatched nucleotides in the BPV life cycle, two mutants clones lacking the bubble region were constructed and their replicative properties were analyzed after electroporation in permissive cells. Infectivity of the mutant clones was determined by three techniques: observation of cytopathic effect, detection of virally-coded proteins by indirect immunofluorescence, and transient DNA replication assays. We report that the mutant clone containing duplicate sequences of the (mismatched) nucleotides numbered 46 to 57 (BLOP) was defective for replication. The other bubbleless clone (BLOM), that contains duplicate sequences of the (mismatched) nucleotides 99 to 105, was able to replicate. The later clone produced monomer-length viral DNA at about 20% of the level of the infectious genomic clone of BPV, when electroporated as a linear excised sequence. This clone was infectious since it could be propagated by subsequent passage. Expression of viral structural proteins was seen by an indirect immunofluorescence assay using anti-capsid antibodies. Our results suggest that the bubble in the left hairpin of BPV is not required for the viral life cycle, but that specific sequences within the mismatched/unpaired region are necessary for viral replication.
- Characterization of the soybean genome in regions surrounding two loci for resistance to soybean mosaic virusHayes, Alec J. (Virginia Tech, 2003-08-01)Soybean mosaic virus (SMV), has been the cause of numerous and often devastating disease epidemics, causing reduction in both the quality and quantity of soybeans worldwide. Two important genes for resistance to SMV are Rsv1 and Rsv4. Alleles at the Rsv1 locus have been shown to control resistance to all but the most virulent strain of SMV. This locus has been mapped previously to the soybean F linkage group. Rsv4 is an SMV resistance locus independent of Rsv1 and confers resistance to all strains of SMV. This locus has not been mapped previously. The purpose of this study is to investigate the two genomic regions that contain these vitally important resistance genes. A population of 281 F2 individuals that had previously been genotyped for reaction to SMV was evaluated in a mapping study which combined bulk segregant analysis with Amplified Fragment Length Polymorphism (AFLP). A Rsv4-linked marker, R4-1, was identified that mapped to soybean linkage group D1b using a reference mapping population. More than 40 markers were mapped in the Rsv4 segregating population including eleven markers surrounding Rsv4. This will provide the necessary framework for the fine mapping of this important genetic locus. Previous work has located Rsv1 to a genomic region containing several important resistance genes including Rps3, Rpg1, and Rpv. An RFLP probe, NBS5, whose sequence closely resembles that of several cloned plant disease resistance genes has been mapped to this chromosomal region. The efficacy of using this sequence to identify potential disease resistance genes was assessed by screening a cDNA library to uncover a candidate disease resistance gene which corresponds to this NBS5 sequence. Two related sequence classes were identified that correspond to NBS5. Interestingly, one class corresponds to a full length gene closely resembling other previously cloned disease resistance genes offering evidence that this NBS5-derived clone is a candidate disease resistance gene. A new marker technique was developed by combining the speed and efficiency of AFLP with DNA sequence information from cloned disease resistance genes. Using this strategy, three new markers tightly linked to Rsv1 were identified. One of these markers, which maps 0.6 cM away from Rsv1, has motifs consistent with other cloned disease resistance genes, providing evidence that this approach is an efficient method for targeting genomic regions where disease resistance genes are located.
- Cis and trans signals for the replication of bovine parvovirusMetcalf, John Brockway (Virginia Tech, 1990)The cis and trans signals important in BPV replication were identified using a transient replication assay, the mobility shift assay, and a comparison between the BPV and LPV genomes. Replication of deleted BPV genomic clones, which contain the natural left (3’ OH end of the viral minus strand) and right (5’ PO, end of the viral minus strand) BPV termini, defined the minimum size of the BPV origin of replication (ori) to be the terminal 171 nucleotides of each terminus. Clones containing duplicate termini or altered left ends were also shown to replicate. The BPV ori was determined to have two domains identified by a computer analysis of homologus regions between these termini. Three proteins were identified that bind to the left terminal 171 nucleotides in the hairpin conformation. Inhibition of the formation of the DNA-protein complexes with competitor DNA localized two potential binding sites that correspond to the domains mentioned above. Two of the DNA-protein complexes were formed by BPV-coded proteins as determined by inhibition of the complex by anti-BPV antibodies. The third complex resulted from binding of a host cell S-phase protein that is a likely candidate for the S-phase factor required for autonomous parvovirus replication. The BPV ori thus appears to function by binding both cellular and viral proteins for the initiation of DNA synthesis from the hairpinned termini. The comparison of the BPV and LPV genome sequence suggest that the genomic organization of LPV may be more like BPV than that of the rodent parvovirus minute virus of mice; and therefore, LPV may contain similar cis signals.
- Controlling Tobacco Mosaic Virus in Tobacco through ResistanceBagley, Christopher A. (Virginia Tech, 2001-12-07)Tobacco mosaic virus (TMV) infects all classes of tobacco (Nicotiana tabacum L.) and causes losses worldwide. The N gene is the most effective means of controlling TMV; however, this gene is associated with reduced yield and quality in flue-cured tobacco. The mode of inheritance of TMV resistance was determined in two tobacco introductions (TI) from N. tabacum germplasm, both of which produced a hypersensitive response when inoculated with TMV. Inheritance studies with TI 1504 and TI 1473 indicate that a single dominant gene controls resistance. The gene governing resistance in TI 1504 is allelic to the N gene in NC 567. The gene providing resistance in TI 1473 is not allelic to the N gene, providing a potentially new source of resistance. Currently, plant breeders must rely on the N gene. The N gene is used in the heterozygous state to help overcome poor agronomic effects associated with homozygous resistance; however, systemic movement of TMV is occasionally seen in resistant plants. A TMV susceptible inbred (K 326), a resistant inbred (NC 567), and three resistant hybrids (NC 297, RGH4, and Speight H2O) were inoculated with TMV at transplanting, layby, and topping using different inoculation methods. Plant parts were tested for viral presence and biological activity. Viral movement into all plant parts was observed in K 326. No systemic movement was evident in the plant parts of NC 567, while virus did move into the corollas, pistils, late season sucker growth, and roots of the resistant hybrids showing systemic necrosis.
- Disease resistant home vegetablesLambe, Robert C.; Tolin, Sue A.; Baldwin, Robert E. (Virginia Cooperative Extension Service, 1980-03)List of specific vegetables to grow in Virginia with their various ratings for disease resistance from very susceptible to highly resistant
- Disease resistant vegetable cultivars for home and marketLambe, Robert C.; Tolin, Sue A.; Baldwin, Robert E. (Virginia Polytechnic Institute and State University. Extension Division, 1987-06)Contains a list of vegetables and their susceptibility to common diseases.
- Documentation of grapevine leafroll-associated viruses in wine grape varieties and native grape species in Virginia, and examination of the movement of grapevine leafroll disease to develop management strategiesJones, Taylor J. (Virginia Tech, 2012-12-21)Grapevine leafroll-associated virus-2 (GLRaV-2), GLRaV-3, and grapevine fleck virus (GFkV) are widespread in grapes around the world. These viruses can cause significant crop loss and affect wine quality by reducing sugar accumulation and compromising skin color. Mealybugs are vectors of grapevine leafroll-associated viruses (GLRaVs). A statewide survey of commercial and wild grapevines in Virginia was conducted during 2009 through 2011. Also, vector management options were tested in two field studies. GLRaV-2, GLRaV-3, and GFkV were detected in 8%, 25%, and 1%, respectively, of over 1,200 vine samples (41 wine grape varieties) from 77 locations, and 64% of vineyards were positive for at least one of the tested viruses. All 100 wild grapevines tested were free of these three viruses, indicating that they are not alternative hosts. The majority of infected vines from commercial vineyards were planted prior to the 1990\'s; however, some new plantings were also found to be positive, indicating movement of the viruses among vineyards and also potential infection prior to planting. The high frequency of virus-infected vines emphasizes the importance of clean plant materials, as well as management of vector insects. The insecticide trials resulted in promising vector control with dinotefuran and spirotetramat; however, acetamiprid and pryrethroid resulted in an increase in mealybug population. This study is the first to examine multiple grape viruses in VA. It will aid in developing better strategies aimed at controlling mealybugs to restrict the movement of viral diseases.
- Effect of postemergence johnsongrass control on MCDV and MDMV incidence and severity in field cornEberwine, John Wright (Virginia Tech, 1996-04-05)In the summers of 1989 and 1990, researchers in Va. and Md. began to observe lateseason reductions in com vigor in areas treated with nicosulfuron or primisulfuron for postemergence johnsongrass control. Symptoms observed included chlorosis, reddening of the leaves and shortening of the internodes. The nature and time of symptom expression were consistent with those caused by maize chlorotic dwarfvirus (MCDV) and maize dwarf mosaic virus (MDMV) infection of com. It was hypothesized that postemergence johnsongrass control increased the incidence and severity of MCDV and MDMV in virus-susceptible corn hybrids due to increased feeding by vectors of these viruses on treated corn. Field experiments were conducted in 1991 and 1992 to evaluate the effect of postemergence johnsongrass control with broad casted nicosulfuron, postemergence directed imazethapyr, mechanical control and no control on virus disease incidence and severity in a virus-susceptible ('Southern States 565') and a virus-tolerant ('Southern States 844) corn hybrid. Visual injury evaluations taken 10 weeks after treatment showed that the virus-susceptible com hybrid sustained significantly more injury, averaged across johnsongrass control methods, than did the virus-tolerant corn hybrid. Within the virus-susceptible com hybrid, where johnsongrass was controlled, regardless of method, significantly more injury was observed relative to the nontreated check. Further, averaged across johnsongrass control treatments, the virus-tolerant corn hybrid yielded significantly higher compared to the virus-susceptible com hybrid. Experiments conducted in 1993 and 1994 utilized cages as a means of preventing insect movement from the infected johnsongrass to the crop. Blackfaced leafhopper evaluations suggested that the cages significantly reduced leafhopper movement from the infected johnsongrass to the corn, however complete exclusion was not achieved. Results of corn tissue assays showed that MCDV and MDMV were being transmitted, however no treatment differences were detected. Two experiments were conducted in 1994 to analytically test the hypothesis and to determine the time course of MCDV and MDMV double infection of corn tissue. Johnsongrass control treatments evaluated included broadcast nicosulfuron and no treatment. Postemergence johnsongrass control increased MCDV and MDMV incidence 9 to 21 days after treatment. Further, significantly more double infections of MCDV and MDMV were observed 14 to 21 days after treatment in experimental units receiving the nicosulfuron application.
- The Effects of Temperature On The Durability Of Resistance Of Soybean To Soybean Mosaic VirusFlora, Jonathan P. (Virginia Tech, 1997-05-08)The objectives of this study were to determine the effects the temperature sensitivity of alleles of Rsv1 in soybean (Glycine max (L.) Merr.). Soybean cultivars carrying alleles of Rsv were exposed to 1 several heat treatments designed to induce heat shock protein production prior to inoculation with soybean mosaic virus (SMV). The heat treatment methods were similar to those employed in the research with N gene-tobacco mosaic virus studies. The soybean cultivars used were Lee 69, York, Kwanggyo, Ogden and PI96983, carrying the Rsv, Rsv1-y, Rsv1-k, Rsv1-t, and Rsv1 allles of Rsv1, respectively, and were selected to provide a range of reactions to selected SMV pathotype groups. For example Rsv1-y and Rsv1-k give a necrotic response to SMV G4 and SMV G6, respectively, while both are resistant to SMV G1. To determine the durability of resistance under heat shock conditions, the symptoms were observed for changes in the phenotype of the resistance response. Immunological techniques were employed to determine the vascular movement and localization of the viral antigen in the plant. Heat treatments used were found to induce HSP but to have no effect on the resistance phenotype. A detached leaf assay was used to test the same Rsv alleles at constant 1 high temperatures. Primary trifoliolate leaflets were removed and inoculated, then placed into a continuously lighted incubator at 20 °C or 30 °C. Leaf immunoprint assays were used to determine the localization of the viral antigen. The visible symptoms for necrotic lesions and veins were observed for necrotic phenotype-pathotype combinations but mosaic symptoms were not observed on detached leaves, as expected for inoculated leaves. The detached leaf assay confirmed that no change from the expected resistance response of the Rsv alleles occurred at 30 C. A breakdown 1 o of resistance to SMV at high temperature had been reported in soybean by Tu and Buzzell (1987). The resistance gene in which the high temperature breakdown occurred has been determined to be Rsv . Using cultivars and breeding lines carrying Rsv a similar experiment was attempted in growth 3 3 chambers. Preliminary results suggest that Rsv is temperature sensitive.
- Epidemiology, Aphid Vectors, Impact and Management of Tobacco Etch Potyvirus in Hot Peppers in JamaicaMcDonald, Sharon Angella (Virginia Tech, 2001-02-22)Production of hot peppers, Capsicum spp., in Jamaica is constrained by the aphid-transmitted potyviruses, tobacco etch virus (TEV) and potato virus Y (PVY). The virus epidemiology was not understood and no effective virus management system existed for these viruses. This study sought to identify possible management strategies for aphid-transmitted viruses of hot peppers in Jamaica, using TEV and Capsicum chinense, var. 'Scotch Bonnet' and 'West Indian Red', as models. Field spread of TEV to pepper was mainly by secondary spread from primary infections. Secondary infections were spatially correlated to primary infections for up to 25 meters. Natural infections of TEV were associated with aphid flight activity. Over 30 species of aphids were collected on pepper farms in St. Catherine parish. These aphids included five known vectors of TEV, Aphis gossypii Glover, A. craccivora Koch, A. spiraecola Patch, Lipaphis erysimi Hille Ris Lambers and M. persicae (Sulzer), and 12 new records for Jamaica, Aphis amaranthi Holman, Brachycaudus helichrysi (Kaltenbach),Capitophorus hippophaes (Walker), Geopemphigus floccosus (Moreira), Hysteroneura setariae (Thomas), Lipaphis erysimi Hille Ris Lambers, Rhopalosiphum padi (Linnaeus), Schizaphis graminum (Rondani), Schizaphis rotundiventris (Signoret), Trichosiphonaphis poligoni (van der Goot), Uroleucon ambrosiae complex (Thomas) and Uroleucon pseudoambrosiae (Olive). A. amaranthi and U. ambrosiae were associated with TEV spread. Weeds on and near farms influenced the abundance and species of aphids captured. West Indian Red pepper showed tolerance to TEV. Scotch Bonnet pepper yield reduction was greater if plants were infected with TEV during the vegetative stage through flower initiation rather than after the start of fruit set. Stylet oil and reflective mulch used together delayed the incidence of TEV in pepper plots for over two months. TEV management programs should aim to delay the virus from infecting peppers during the first two months after transplanting. A risk analysis is proposed for management of TEV and other aphid-borne viruses.
- Evolution of a gene for pathogenicity: endo-pectate lyaseAllen, Caitilyn (Virginia Polytechnic Institute and State University, 1987)Erwinia carotovora subsp. Carotovora (Ecc) and Erwinia carotovora subsp. Atroseptica (Eca) are plant pathogenic bacteria that cause soft rot disease of many plant species and blackleg disease of potatoes, respectively. Ecc and Eca attack plants by means of a group of extracellular plant tissue-degrading enzymes. which rapidly breaks down the pectic polymers that form a structurally important part of the plant cell wall, is considered central to soft rot pathogenesis. In this work, I isolated and studied the genes encoding this enzyme from Ecc and Eca. A clone library of Ecc strain EC14 was constructed using cosmid PLAFR3. This library contains 2,200 clones with an average insert size of 27 kilobases of DNA and included a proteolytic clone, five cellulolytic clones, and ten pectolytic clones. The proteolytic clone was used to complement a Tn5-induced protease mutant of Ecc; the complemented mutant was restored to near-wild type phenotype. Six of the pectolytic clones hybridized to a probe from a. previously isolated extracellular endo-pectate-pectate lyase gene from Ecc; one pectolytic clone had homology to a previously isolated clone encoding endo-polygalacturonase: three clones showed no relationship to either of the previously characterized Ecc pectolytic enzyme genes. A clone encoding the major endo-pectate lyase gene from Ecc was chosen for subcloning and further study. I used the plasmid vector pBR322 to construct a clone bank of Eca strain SRB; of the 1700 clones screened, five were pectolytic. Two of the Eca pectolytic. clones had homology to the Ecc endo-pectate lyase gene; upon examination, they proved to contain the same insert in opposite orientations. The Ecc endo-pectate lyase had a pI of 9. 5 and a molecular weight of 33,000; the analogous Eca endo-pectate lyase had a pI of 9.2 and a molecular weight of 31,000. Both enzymes required a divalent cation for activity (preferring Ca2+ over Mg2+ over Mn²⁺. The restriction endonuclease maps of the two clones did not have any tested sites in common. These differences suggest that although these two genes may have originated from a common ancestral gene, considerable divergence has taken place. I analyzed the fine structure of the Ecc endo-pectate lyase gene by DNA sequencing. The coding region of the gene is preceded by E. coli-type -10 and -35 sequences and encodes an unmodified protein of 281 amine acids. A typical secretion signal peptide is not present.
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