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Stephen K Gray - One of the best experts on this subject based on the ideXlab platform.
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evidence of the biochemical basis of host virulence in the greenbug aphid Schizaphis Graminum homoptera aphididae
Journal of Proteome Research, 2014Co-Authors: Patricia V Pinheiro, Stephen K Gray, John D Burd, Michael S Bereman, Melissa Pals, Scott Armstrong, Kevin J Howe, Theodore W Thannhauser, Michael J Maccoss, Michelle CiliaAbstract:Biotypes of aphids and many other insect pests are defined based on the phenotypic response of host plants to the insect pest without considering their intrinsic characteristics and genotypes. Plant breeders have spent considerable effort developing aphid-resistant, small-grain varieties to limit insecticide control of the greenbug, Schizaphis Graminum. However, new S. Graminum biotypes frequently emerge that break resistance. Mechanisms of virulence on the aphid side of the plant–insect interaction are not well understood. S. Graminum biotype H is highly virulent on most small grain varieties. This characteristic makes biotype H ideal for comparative proteomics to investigate the basis of biotype virulence in aphids. In this study, we used comparative proteomics to identify protein expression differences associated with virulence. Aphid proteins involved in the tricarboxylic acid cycle, immune system, cell division, and antiapoptosis pathways were found to be up-regulated in biotype H relative to other b...
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biometrical genetic analysis of luteovirus transmission in the aphid Schizaphis Graminum
Heredity, 2007Co-Authors: M E Burrows, Marina C Caillaud, Dawn M Smith, Stephen K GrayAbstract:The aphid Schizaphis Graminum is an important vector of the viruses that cause barley yellow dwarf disease. We studied the genetic architecture of virus transmission by crossing a vector and a non-vector genotype of S. Graminum. F1 and F2 hybrids were generated, and a modified line-cross biometrical analysis was performed on transmission phenotype of two of the viruses that cause barley yellow dwarf: Cereal yellow dwarf virus (CYDV)-RPV and Barley yellow dwarf virus (BYDV)-SGV. Our aims were to (1) determine to what extent differences in transmission ability between vectors and non-vectors is due to net additive or non-additive gene action, (2) estimate the number of loci that determine transmission ability and (3) examine the nature of genetic correlations between transmission of CYDV-RPV and BYDV-SGV. Only additive effects contributed significantly to divergence in transmission of both CYDV-RPV and BYDV-SGV. For each luteovirus, Castle–Wright's estimator for the number of effective factors segregating for transmission phenotype was less than one. Transmission of CYDV-RPV and BYDV-SGV was significantly correlated in the F2 generation, suggesting that there is a partial genetic overlap for transmission of these luteoviruses. Yet, 63% of the F2 genotypes transmitted CYDV-RPV and BYDV-SGV at significantly different rates. Our data suggest that in S. Graminum, the transmission efficiency of both CYDV-RPV and BYDV-SGV is regulated by a major gene or set of tightly linked genes, and the transmission efficiency of each virus is influenced by a unique set of minor genes.
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genetic regulation of polerovirus and luteovirus transmission in the aphid Schizaphis Graminum
Phytopathology, 2006Co-Authors: M E Burrows, Marina C Caillaud, Dawn M Smith, E C Benson, F E Gildow, Stephen K GrayAbstract:Burrows, M. E., Caillaud, M. C., Smith, D. M., Benson, E. C., Gildow, F. E., and Gray, S. M. 2006. Genetic regulation of polerovirus and luteovirus transmission in the aphid Schizaphis Graminum. Phytopathology 96:828837. Sexual forms of two genotypes of the aphid Schizaphis Graminum, one a vector, the other a nonvector of two viruses that cause barley yellow dwarf disease (Barley yellow dwarf virus [BYDV]-SGV, luteovirus and Cereal yellow dwarf virus-RPV, polerovirus), were mated to generate F1 and F2 populations. Segregation of the transmission phenotype for both viruses in the F1 and F2 populations indicated that the transmission phenotype is under genetic control and that the parents are heterozygous for genes involved in transmission. The ability to transmit both viruses was correlated within the F1 and F2 populations, suggesting that a major gene or linked genes regulate the transmission. However, individual hybrid genotypes differed significantly in their ability to transmit each virus, indicating that in addition to a major gene, minor genes can affect the transmission of each virus independently. Gut and salivary gland associated transmission barriers were identified in the nonvector parent and some progeny, while other progeny possessed only a gut barrier or a salivary gland barrier. Hemolymph factors do not appear to be involved in determining the transmission phenotype. These results provide direct evidence that aphid transmission of luteoviruses is genetically regulated in the insect and that the tissue-specific barriers to virus transmission are not genetically linked.
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virus transmission phenotype is correlated with host adaptation among genetically diverse populations of the aphid Schizaphis Graminum
Phytopathology, 2002Co-Authors: Stephen K Gray, Dawn M Smith, Lia Barbierri, John D BurdAbstract:ABSTRACT Schizaphis Graminum is an important insect pest of several grain crops and an efficient vector of cereal-infecting luteoviruses and poleroviruses. We examined the virus transmission characteristics of several distinct populations and various developmental stages of the aphid. Seven well-characterized S. Graminum biotypes maintained at the USDA-ARS laboratory in Stillwater, OK, and two biotypes maintained in New York (one collected in Wisconsin and the other collected in South Carolina) were tested for their ability to transmit five viruses that cause barley yellow dwarf disease (BYD). Four of the Oklahoma biotypes, which do not commonly colonize agronomic crops, and the Wisconsin biotype, were efficient vectors of several viruses. The three other Oklahoma biotypes, which do colonize agronomic crops, and the South Carolina biotype, were poor vectors of all five viruses. Thus, the vector specificity long associated with viruses causing BYD is not limited to the level of aphid species; it clearly ex...
William C Black - One of the best experts on this subject based on the ideXlab platform.
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variation in the ribosomal rna cistron among host adapted races of an aphid Schizaphis Graminum
Insect Molecular Biology, 1993Co-Authors: William C BlackAbstract:The greenbug, Schizaphis Graminum, is an aphid species that consists of races that can be separated based on morphology, life histories, cytogenetics, mitochondrial DNA RFLPs and virulence to plant culti-vars. Variation in the greenbug rDNA multigene family was studied to determine the extent to which rDNA cistrons have diverged among and within races. A restriction map of the rDNA cistron was constructed. Probing DNA from different races with subclones from rDNA coding regions and internal spacers identified little variation. However, probing with subclones of the intergenic spacer (IGS) identified continuous length variation within and among races. Race specific patterns were identified. Within a race, almost continuous variation in total IGS length was detected and asexual lineages possessed distinct patterns useful in genetic fingerprinting studies.
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Variation in the ribosomal RNA cistron among host‐adapted races of an aphid (Schizaphis Graminum)
Insect Molecular Biology, 1993Co-Authors: William C BlackAbstract:: The greenbug, Schizaphis Graminum, is an aphid species that consists of races that can be separated based on morphology, life histories, cytogenetics, mitochondrial DNA RFLPs and virulence to plant cultivars. Variation in the greenbug rDNA multigene family was studied to determine the extent to which rDNA cistrons have diverged among and within races. A restriction map of the rDNA cistron was constructed. Probing DNA from different races with subclones from rDNA coding regions and internal spacers identified little variation. However, probing with subclones of the intergenic spacer (IGS) identified continuous length variation within and among races. Race specific patterns were identified. Within a race, almost continuous variation in total IGS length was detected and asexual lineages possessed distinct patterns useful in genetic fingerprinting studies.
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variation between biotype e clones of Schizaphis Graminum homoptera aphididae
Bulletin of Entomological Research, 1992Co-Authors: Kevin A Shufran, David C Margolies, William C BlackAbstract:Phenotypic and genotypic variation was investigated between biotype E clones of the greenbug, Schizaphis Graminum (Rondani). S. Graminum was collected from wheat and sorghum fields in seven Kansas counties, USA. Colonies representing single maternal lineages (clones) were initiated and maintained in an insectary, and were verified as biotype E. An allozyme survey among clones did not detect any polymorphism at 24 enzymatic loci. We were unable to detect interclonal variation for nymphal survivorship, age at first reproduction, fecundity, and reproductive lifespan. Variation among genetically homogeneous daughters within clones was as great as variation among different clones for the above parameters, due to microenvironmental effects. However, by using the intergenic spacer in the rDNA cistron as a molecular fingerprinting tool, we identified 56 unique maternal lineages among 61 clones tested. The length of the intergenic spacer varied within individual S. Graminum , and different maternal lineages had unique sets of spacer sizes. However, S. Graminum within a single clone shared the same sets of spacer sizes. Extensive molecular genetic variation was found among biotype E clones, despite a lack of variation in additive genetic traits. Thus, biotype E populations are made up of many genetically distinct clones and do not represent an asexual proliferation of one or a few maternal lineages.
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genome size and organization in an aphid Schizaphis Graminum
Journal of Insect Physiology, 1992Co-Authors: Runlin Zhang, William C Black, John C ReeseAbstract:Abstract There is currently no information on genome organization in any paurometabolous insect. DNA reassociation kinetics were used to determine genome size and organization in the greenbug ( Schizaphis Graminum , Rondani). A genome size of 0.40 pg (387×10 6 base pairs) was estimated consisting of 2.4% fold-back sequences, 19.64% middle repetitive sequences and 77.96% unique sequences. The repetitive sequences were distributed in a pattern of long period interspersion. In contrast with species with genome sizes equivalent or smaller in size, the greenbug has very little highly repetitive DNA.
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detection of pectinesterase and polygalacturonase from salivary secretions of living greenbugs Schizaphis Graminum homoptera aphididae
Journal of Insect Physiology, 1990Co-Authors: Runlin Z, William C Black, John C Reese, P J BramelcoxAbstract:Abstract Pectinesterase (EC 3.1.1.11) and polygalacturonase (EC 3.1.1.15) were successfully detected in induced salivary secretions of living greenbugs, Schizaphis Graminum (Rondani). The method involved the construction of agarose-pectin gel plates on which the aphids were allowed to feed through Parafilm, followed by staining of the gels with ruthenium red. The specific activities of pectinesterase and polygalacturonase were detected by formation of dark red circular and clear halos, respectively, around the site of stylet sheaths left by the aphids. The assay indicates the saliva of biotypes E and C contains both enzymes. The method combines a living, feeding organism with an enzyme assay system in a unique and simple way and provides conclusive evidence for the nature of secreted materials. It also provides an opportunity to investigate the formation of stylet sheaths by this and other aphid species. The toxicity of the enzymes to host plants and the importance of the enzymes to greenbug feeding are discussed.
John D Burd - One of the best experts on this subject based on the ideXlab platform.
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evidence of the biochemical basis of host virulence in the greenbug aphid Schizaphis Graminum homoptera aphididae
Journal of Proteome Research, 2014Co-Authors: Patricia V Pinheiro, Stephen K Gray, John D Burd, Michael S Bereman, Melissa Pals, Scott Armstrong, Kevin J Howe, Theodore W Thannhauser, Michael J Maccoss, Michelle CiliaAbstract:Biotypes of aphids and many other insect pests are defined based on the phenotypic response of host plants to the insect pest without considering their intrinsic characteristics and genotypes. Plant breeders have spent considerable effort developing aphid-resistant, small-grain varieties to limit insecticide control of the greenbug, Schizaphis Graminum. However, new S. Graminum biotypes frequently emerge that break resistance. Mechanisms of virulence on the aphid side of the plant–insect interaction are not well understood. S. Graminum biotype H is highly virulent on most small grain varieties. This characteristic makes biotype H ideal for comparative proteomics to investigate the basis of biotype virulence in aphids. In this study, we used comparative proteomics to identify protein expression differences associated with virulence. Aphid proteins involved in the tricarboxylic acid cycle, immune system, cell division, and antiapoptosis pathways were found to be up-regulated in biotype H relative to other b...
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over summering and biotypic diversity of Schizaphis Graminum homoptera aphididae populations on noncultivated grass hosts
Environmental Entomology, 2003Co-Authors: James A Anstead, John D Burd, Kevin A ShufranAbstract:Greenbug, Schizaphis Graminum (Rondani), populations over-summering on noncultivated grass hosts may be implicated in early fall infestations in wheat. The purpose of this study was to examine the relationship between over-summering greenbugs on noncrop hosts and fall infestations on wheat. Since greenbug populations on noncultivated hosts may also act as reservoirs of virulence genes, the biotypes of collected aphids were also determined. The grass species present at three sites (two in Oklahoma and one in Kansas) were identified and a species richness curve was generated. Greenbugs were collected at these sites and their hosts and biotypes determined. At Hays, KS, a persistent over-summering greenbug population lead to an early fall infestation in wheat. At the sites in Oklahoma, where over-summering greenbugs were not detected, the fall infestation occurred 3 months later. Biotypes G, I, K, and a new biotype (i.e., previously undescribed) were found on noncultivated hosts at Hays, but only biotypes I and K were found on the cultivated wheat. Finding a new biotype supports the hypothesis that biotypic diversity (new combinations of virulence genes) is generated and maintained on noncultivated grasses, which may then act as reservoirs of virulence genes found in populations on crops.
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virus transmission phenotype is correlated with host adaptation among genetically diverse populations of the aphid Schizaphis Graminum
Phytopathology, 2002Co-Authors: Stephen K Gray, Dawn M Smith, Lia Barbierri, John D BurdAbstract:ABSTRACT Schizaphis Graminum is an important insect pest of several grain crops and an efficient vector of cereal-infecting luteoviruses and poleroviruses. We examined the virus transmission characteristics of several distinct populations and various developmental stages of the aphid. Seven well-characterized S. Graminum biotypes maintained at the USDA-ARS laboratory in Stillwater, OK, and two biotypes maintained in New York (one collected in Wisconsin and the other collected in South Carolina) were tested for their ability to transmit five viruses that cause barley yellow dwarf disease (BYD). Four of the Oklahoma biotypes, which do not commonly colonize agronomic crops, and the Wisconsin biotype, were efficient vectors of several viruses. The three other Oklahoma biotypes, which do colonize agronomic crops, and the South Carolina biotype, were poor vectors of all five viruses. Thus, the vector specificity long associated with viruses causing BYD is not limited to the level of aphid species; it clearly ex...
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mitochondrial dna sequence divergence among Schizaphis Graminum hemiptera aphididae clones from cultivated and non cultivated hosts haplotype and host associations
Bulletin of Entomological Research, 2002Co-Authors: James A Anstead, John D Burd, Kevin A ShufranAbstract:A 1.0 kb region of the mitochondrial cytochrome oxidase subunit I gene from the greenbug aphid, Schizaphis Graminum (Rondani), was sequenced for 24 field collected clones from non-cultivated and cultivated hosts. Maximum likelihood, maximum parsimony and neighbour-joining phylogenies were estimated for these clones, plus 12 previously sequenced clones. All three tests produced trees with identical topologies and confirmed the presence of three clades within S. Graminum. Clones showed no relationship between biotype and mtDNA haplotype. At least one biotype was found in all three clades, suggesting exchange among clades of genetic material conditioning for crop virulence, or the sharing of a common ancestor. However, there was a relationship between host and haplotype. Clade 1 was the most homogenous and contained 12 of 16 clones collected from cultivated hosts and five of the six collected from johnsongrass, Sorghum halepense, a congener of cultivated sorghum, S. bicolor. Four of the six clones collected from Agropyron spp. were found in clade 2. Clade 3 contained two clones from wheat, Triticum aestivum, and four from non-cultivated hosts other than Agropyron spp. A partitioning of populations by mtDNA haplotype and host suggests the occurrence of host adapted races in Schizaphis Graminum.
Dawn M Smith - One of the best experts on this subject based on the ideXlab platform.
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biometrical genetic analysis of luteovirus transmission in the aphid Schizaphis Graminum
Heredity, 2007Co-Authors: M E Burrows, Marina C Caillaud, Dawn M Smith, Stephen K GrayAbstract:The aphid Schizaphis Graminum is an important vector of the viruses that cause barley yellow dwarf disease. We studied the genetic architecture of virus transmission by crossing a vector and a non-vector genotype of S. Graminum. F1 and F2 hybrids were generated, and a modified line-cross biometrical analysis was performed on transmission phenotype of two of the viruses that cause barley yellow dwarf: Cereal yellow dwarf virus (CYDV)-RPV and Barley yellow dwarf virus (BYDV)-SGV. Our aims were to (1) determine to what extent differences in transmission ability between vectors and non-vectors is due to net additive or non-additive gene action, (2) estimate the number of loci that determine transmission ability and (3) examine the nature of genetic correlations between transmission of CYDV-RPV and BYDV-SGV. Only additive effects contributed significantly to divergence in transmission of both CYDV-RPV and BYDV-SGV. For each luteovirus, Castle–Wright's estimator for the number of effective factors segregating for transmission phenotype was less than one. Transmission of CYDV-RPV and BYDV-SGV was significantly correlated in the F2 generation, suggesting that there is a partial genetic overlap for transmission of these luteoviruses. Yet, 63% of the F2 genotypes transmitted CYDV-RPV and BYDV-SGV at significantly different rates. Our data suggest that in S. Graminum, the transmission efficiency of both CYDV-RPV and BYDV-SGV is regulated by a major gene or set of tightly linked genes, and the transmission efficiency of each virus is influenced by a unique set of minor genes.
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genetic regulation of polerovirus and luteovirus transmission in the aphid Schizaphis Graminum
Phytopathology, 2006Co-Authors: M E Burrows, Marina C Caillaud, Dawn M Smith, E C Benson, F E Gildow, Stephen K GrayAbstract:Burrows, M. E., Caillaud, M. C., Smith, D. M., Benson, E. C., Gildow, F. E., and Gray, S. M. 2006. Genetic regulation of polerovirus and luteovirus transmission in the aphid Schizaphis Graminum. Phytopathology 96:828837. Sexual forms of two genotypes of the aphid Schizaphis Graminum, one a vector, the other a nonvector of two viruses that cause barley yellow dwarf disease (Barley yellow dwarf virus [BYDV]-SGV, luteovirus and Cereal yellow dwarf virus-RPV, polerovirus), were mated to generate F1 and F2 populations. Segregation of the transmission phenotype for both viruses in the F1 and F2 populations indicated that the transmission phenotype is under genetic control and that the parents are heterozygous for genes involved in transmission. The ability to transmit both viruses was correlated within the F1 and F2 populations, suggesting that a major gene or linked genes regulate the transmission. However, individual hybrid genotypes differed significantly in their ability to transmit each virus, indicating that in addition to a major gene, minor genes can affect the transmission of each virus independently. Gut and salivary gland associated transmission barriers were identified in the nonvector parent and some progeny, while other progeny possessed only a gut barrier or a salivary gland barrier. Hemolymph factors do not appear to be involved in determining the transmission phenotype. These results provide direct evidence that aphid transmission of luteoviruses is genetically regulated in the insect and that the tissue-specific barriers to virus transmission are not genetically linked.
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virus transmission phenotype is correlated with host adaptation among genetically diverse populations of the aphid Schizaphis Graminum
Phytopathology, 2002Co-Authors: Stephen K Gray, Dawn M Smith, Lia Barbierri, John D BurdAbstract:ABSTRACT Schizaphis Graminum is an important insect pest of several grain crops and an efficient vector of cereal-infecting luteoviruses and poleroviruses. We examined the virus transmission characteristics of several distinct populations and various developmental stages of the aphid. Seven well-characterized S. Graminum biotypes maintained at the USDA-ARS laboratory in Stillwater, OK, and two biotypes maintained in New York (one collected in Wisconsin and the other collected in South Carolina) were tested for their ability to transmit five viruses that cause barley yellow dwarf disease (BYD). Four of the Oklahoma biotypes, which do not commonly colonize agronomic crops, and the Wisconsin biotype, were efficient vectors of several viruses. The three other Oklahoma biotypes, which do colonize agronomic crops, and the South Carolina biotype, were poor vectors of all five viruses. Thus, the vector specificity long associated with viruses causing BYD is not limited to the level of aphid species; it clearly ex...
Kevin A Shufran - One of the best experts on this subject based on the ideXlab platform.
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host race evolution in Schizaphis Graminum hemiptera aphididae nuclear dna sequences
Environmental Entomology, 2011Co-Authors: Kevin A ShufranAbstract:ABSTRACT The greenbug aphid, Schizaphis Graminum (Rondani) was introduced into the United States in the late 1880s, and quickly was established as a pest of wheat, oat, and barley. Sorghum was also a host, but it was not until 1968 that greenbug became a serious pest of it as well. The most effective control method is the planting of resistant varieties; however, the occurrence of greenbug biotypes has hampered the development and use of plant resistance as a management technique. Until the 1990s, the evolutionary status of greenbug biotypes was obscure. Four mtDNA cytochrome oxidase subunit I (COI) haplotypes were previously identified, suggesting that S. Graminum sensu lato was comprised of host-adapted races. To elucidate the current evolutionary and taxonomic status of the greenbug and its biotypes, two nuclear genes and introns were sequenced; cytochrome c (CytC) and elongation factor 1-α (EF1-α). Phylogenetic analysis of CytC sequences were in complete agreement with COI sequences and demonstrated t...
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over summering and biotypic diversity of Schizaphis Graminum homoptera aphididae populations on noncultivated grass hosts
Environmental Entomology, 2003Co-Authors: James A Anstead, John D Burd, Kevin A ShufranAbstract:Greenbug, Schizaphis Graminum (Rondani), populations over-summering on noncultivated grass hosts may be implicated in early fall infestations in wheat. The purpose of this study was to examine the relationship between over-summering greenbugs on noncrop hosts and fall infestations on wheat. Since greenbug populations on noncultivated hosts may also act as reservoirs of virulence genes, the biotypes of collected aphids were also determined. The grass species present at three sites (two in Oklahoma and one in Kansas) were identified and a species richness curve was generated. Greenbugs were collected at these sites and their hosts and biotypes determined. At Hays, KS, a persistent over-summering greenbug population lead to an early fall infestation in wheat. At the sites in Oklahoma, where over-summering greenbugs were not detected, the fall infestation occurred 3 months later. Biotypes G, I, K, and a new biotype (i.e., previously undescribed) were found on noncultivated hosts at Hays, but only biotypes I and K were found on the cultivated wheat. Finding a new biotype supports the hypothesis that biotypic diversity (new combinations of virulence genes) is generated and maintained on noncultivated grasses, which may then act as reservoirs of virulence genes found in populations on crops.
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mitochondrial dna sequence divergence among Schizaphis Graminum hemiptera aphididae clones from cultivated and non cultivated hosts haplotype and host associations
Bulletin of Entomological Research, 2002Co-Authors: James A Anstead, John D Burd, Kevin A ShufranAbstract:A 1.0 kb region of the mitochondrial cytochrome oxidase subunit I gene from the greenbug aphid, Schizaphis Graminum (Rondani), was sequenced for 24 field collected clones from non-cultivated and cultivated hosts. Maximum likelihood, maximum parsimony and neighbour-joining phylogenies were estimated for these clones, plus 12 previously sequenced clones. All three tests produced trees with identical topologies and confirmed the presence of three clades within S. Graminum. Clones showed no relationship between biotype and mtDNA haplotype. At least one biotype was found in all three clades, suggesting exchange among clades of genetic material conditioning for crop virulence, or the sharing of a common ancestor. However, there was a relationship between host and haplotype. Clade 1 was the most homogenous and contained 12 of 16 clones collected from cultivated hosts and five of the six collected from johnsongrass, Sorghum halepense, a congener of cultivated sorghum, S. bicolor. Four of the six clones collected from Agropyron spp. were found in clade 2. Clade 3 contained two clones from wheat, Triticum aestivum, and four from non-cultivated hosts other than Agropyron spp. A partitioning of populations by mtDNA haplotype and host suggests the occurrence of host adapted races in Schizaphis Graminum.
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Clonal diversity in overwintering populations of Schizaphis Graminum (Homoptera: Aphididae)
Bulletin of Entomological Research, 1994Co-Authors: Kevin A Shufran, Gerald E. WildeAbstract:AbstractThe intergenic spacer region of the rRNA cistron was used as a molecular fingerprinting probe to study clonal diversity in Schizaphis Graminum (Rondani). A high degree of clonal diversity was found in overwintering populations on wheat from Kansas, Texas and Oklahoma. Out of 184 individuals tested, 132 unique maternal lineages wereidentified. Overall, clonal diversity of overwintering populations was no less than in spring and summer populations. However, in some fields there were more instances where individuals of the same genotype were identified. By partitioning the total population diversity into various sampling components (fields, counties and states), 93.1% of the total diversity was found among individual S. Graminum within fields. Overwintering of many genetically distinct clones as parthenogenetic morphs is one mechanism by which clonal diversity is maintained in populations of S. Graminum. The incidence of clonal diversity further substantiates the importance of the S. Graminum holocycle for generating genetic heterogeneity in the USA.
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variation between biotype e clones of Schizaphis Graminum homoptera aphididae
Bulletin of Entomological Research, 1992Co-Authors: Kevin A Shufran, David C Margolies, William C BlackAbstract:Phenotypic and genotypic variation was investigated between biotype E clones of the greenbug, Schizaphis Graminum (Rondani). S. Graminum was collected from wheat and sorghum fields in seven Kansas counties, USA. Colonies representing single maternal lineages (clones) were initiated and maintained in an insectary, and were verified as biotype E. An allozyme survey among clones did not detect any polymorphism at 24 enzymatic loci. We were unable to detect interclonal variation for nymphal survivorship, age at first reproduction, fecundity, and reproductive lifespan. Variation among genetically homogeneous daughters within clones was as great as variation among different clones for the above parameters, due to microenvironmental effects. However, by using the intergenic spacer in the rDNA cistron as a molecular fingerprinting tool, we identified 56 unique maternal lineages among 61 clones tested. The length of the intergenic spacer varied within individual S. Graminum , and different maternal lineages had unique sets of spacer sizes. However, S. Graminum within a single clone shared the same sets of spacer sizes. Extensive molecular genetic variation was found among biotype E clones, despite a lack of variation in additive genetic traits. Thus, biotype E populations are made up of many genetically distinct clones and do not represent an asexual proliferation of one or a few maternal lineages.
