No description available.

Greenbug is one of two key insect pests of sorghum, and biotype evolution hinders the long-term usefulness of resistant sorghums. The current study sought to identify plant resistance mechanisms, plant damage characteristics, and greenbug fitness in sorghum/greenbug interactions. Choice tests were conducted to elucidate resistance mechanisms displayed by four sorghum genotypes towards several greenbug biotypes and isolates. Results indicated all three resistance modalities (antibiosis, antixenosis, tolerance) were identified in sorghums, with some genotypes displaying two or more modalities towards some biotypes. This suggests some sorghum genotypes do not select for greenbug biotypes, and the sorghum genotypes cultivated may have relatively long-term resistance. Non-choice tests were used to determine plant damage associated with greenbug feeding. Four sorghum genotype, Johnson grass, and five greenbug biotype combinations were used to elucidate plant characteristics associated with visible plant damage. Fluid loss and plant stunting were significantly associated with visible plant damage, and were also observed in some plants not incurring heavy visible damage. Additionally, some biotypes avirulent to cultivated sorghum caused significant damage to Johnson grass. These results suggest visible plant damage, routinely used in damage studies, reflects underlying causes that could lead to poor agronomic performance. Additionally, Johnson grass may harbor greenbug biotypes not commonly found in sorghum fields. Greenbug colony and individual fitness were determined by reproduction rates of five biotypes on four sorghum genotypes and Johnson grass in non-choice tests. Generally, colony and individual fitness estimates were not different within genotype/biotype combinations. Also, biotypes did best on more susceptible and worst on more resistant sorghum genotypes. Colonies and individuals of all biotypes had lowest fitness on Johnson grass. These results suggest virulent biotypes may have a fitness advantage over avirulent ones, at least in the presence of the cultivated host. The results presented herein reflect the diversity of sorghum/greenbug interactions, and underscore the need for further understanding of the nature of greenbug biotypes, and how they interact with cultivated and non-cultivated host plants.

Reciprocal and homologous crosses were carried out using pairs or groups of twenty males and females for three biotypes of the whitefly Bemisia tabaci complex. Crosses were undertaken for the A biotype-Arizona (AzA), the B biotype-Africa (AzB), and the monophagous, Jatropha (Jat) biotype-Puerto Rico. The maternal haplotype pedigree of parents and selected offspring (F₁, F₂) was determined using the mitochondria cytochome oxidase I sequence. All reciprocal crosses yielded viable female offspring, indicating reproductively compatibility, except for AzB♀ x AzA♂, or AzB♀ x Jat♂ crosses, which yielded females unidirectionally. As an unidirectional pattern was reminiscent of cytoplasmic-mediated incompatibility (CI), the possibility was investigated that the phenotype might be caused by CI-bacteria, instead of a germ line barrier. Using the 16S rRNA sequence three prospective CI-bacterial species were identified in whitefly colonies. A Cardinium spp. (Bacteroidetes) was present in the A biotype (isolates AzA, CulA, RivA, SalA), whereas the B biotype (isolates AzB, FlB1, FlB2) was infected with Rickettsia bellii (Proteobacteria), and a Wolbachia spp. (Proteobacteria) was associated with the Jat biotype. The unidirectional incompatible phenotypes were consistent with CI-bacterial infection of AzA (Cardinium) and Jat (Wolbachia), but no such association was apparent for B biotype-Rickettsia infections. The bidirectional compatibility for Jat x AzA suggested a CI-bacteria-mediated reciprocal rescue. However, that Wolbachia-infected Jat♀ and Cardinium-infected AzA♂ crosses yielded fewer females, compared to AzA-Cardinium♀ and Jat- Wolbachia♂ crosses, suggested that Cardinium could better counter Wolbachia-induced female mortality than Wolbachia. This suggested the possibility that these phylogenetically divergent bacteria might utilize similar CI-mechanisms. In this study, the suspect CI-bacteria were strongly associated with complete or partial obstruction of gene flow in certain crosses, and with sex bias in the AzA x Jat crosses. This is the first evidence that female offspring can be produced between phylogeographically divergent, and polyphagous and monophagous B. tabaci, for which gene flow barriers are widely reported, suggesting that hybridization is utilized as a means of diversification in B. tabaci. The inability to rid colonies of CI-bacteria has necessitated introgression experiments to investigate direct CI-causality over CI-association.

Greenbug is one of two key insect pests of sorghum, and biotype evolution hinders the long-term usefulness of resistant sorghums. The current study sought to identify plant resistance mechanisms, plant damage characteristics, and greenbug fitness in sorghum/greenbug interactions. Choice tests were conducted to elucidate resistance mechanisms displayed by four sorghum genotypes towards several greenbug biotypes and isolates. Results indicated all three resistance modalities (antibiosis, antixenosis, tolerance) were identified in sorghums, with some genotypes displaying two or more modalities towards some biotypes. This suggests some sorghum genotypes do not select for greenbug biotypes, and the sorghum genotypes cultivated may have relatively long-term resistance. Non-choice tests were used to determine plant damage associated with greenbug feeding. Four sorghum genotype, Johnson grass, and five greenbug biotype combinations were used to elucidate plant characteristics associated with visible plant damage. Fluid loss and plant stunting were significantly associated with visible plant damage, and were also observed in some plants not incurring heavy visible damage. Additionally, some biotypes avirulent to cultivated sorghum caused significant damage to Johnson grass. These results suggest visible plant damage, routinely used in damage studies, reflects underlying causes that could lead to poor agronomic performance. Additionally, Johnson grass may harbor greenbug biotypes not commonly found in sorghum fields. Greenbug colony and individual fitness were determined by reproduction rates of five biotypes on four sorghum genotypes and Johnson grass in non-choice tests. Generally, colony and individual fitness estimates were not different within genotype/biotype combinations. Also, biotypes did best on more susceptible and worst on more resistant sorghum genotypes. Colonies and individuals of all biotypes had lowest fitness on Johnson grass. These results suggest virulent biotypes may have a fitness advantage over avirulent ones, at least in the presence of the cultivated host. The results presented herein reflect the diversity of sorghum/greenbug interactions, and underscore the need for further understanding of the nature of greenbug biotypes, and how they interact with cultivated and non-cultivated host plants.

Diuraphis noxia Kurdjumov (Hemiptera: Aphididae: Macrosiphini) is a major agricultural pest that causes extensive economic losses to the wheat and barley industries. Resistant cultivars were relatively successful in controlling this pest until the recent development of new D. noxia (Russian wheat aphid, RWA) biotypes. The aim was to investigate the role of the aphid endosymbiont, Buchnera aphidicola, in the RWA-host interaction. It was hypothesized that variations in the endosymbiont’s key essential amino acid biosynthetic pathway genes, their copy numbers, and/or expression levels, maybe a determining factor influence the RWA’s success in the aphid-host interaction. Aphid symbiont species content, key essential amino acid biosynthetic gene variation, plasmid copy numbers and expression levels of ten different RWA biotypes were determined, using DGGE, RT-PCR, RT-qPCR, 5’-RACE and sequencing. The RWA biotypes were shown to be monosymbiotic, with plasmid copy numbers varying between biotypes. Only a single CCC-insert in a non-coding region of the leucine plasmid differed between the biotypes. Similar variations were identified in the family Aphididae, suggesting a regulatory function for this region. The presence of this CCC-insert in a plasmid led to an increase in the leader sequence length of the leuA gene. The insert may also have a functional role through gene regulation, since it increased the expression levels of subsequent genes (leuA and leuB). An endosymbiont that upgrade the host’s diet with the required essential amino acids will be beneficial to RWAs when feeding on resistant wheat cultivars as it will enhance aphid fitness. This suggests selective pressure of resistant wheat cultivars on the aphid, i.e. the incapability to change resistant cultivar essential amino acid content, could select for individuals with beneficial endosymbionts. B. aphidicola could therefore play a role in the development of RWA biotypes. The influences that statistical normalization methods have on the final identification of differentially regulated Affymetrix probe sets in RWA-plant interactions were also investigated. The hypothesis was that a subset of the probe sets determined as differentially regulated would be consistent, regardless of the normalization and background method utilized, if all the other analyses are kept constant. This subset would be normalization-method-independent. The data of two Affymetrix RWA-plant interaction experiments were analyzed with five different normalization and background correcting methods and at three different confidence levels, with the results subjected to FDR and FWER correction algorithms. The results showed that on average a third of the regulated genes were only selected after normalization by a single method and that the total number of genes deemed regulated was highly normalization method dependent. Normalization-method-biases could also not be countered by increased confidence levels and these biases eventually determined the probe sets deemed differentially regulated, even after FDR and FWER corrections. Both these strategies actually increased normalization-method-biases and these could only be corrected by using multiple normalization methods to identify the normalization-method-biases-independent probe set subset. / Thesis (PhD)--University of Pretoria, 2011. / Genetics / unrestricted

Bacterial endosymbionts can have profound impacts on their host’s ecology. Notably, endosymbionts can protect their hosts against natural enemies and influence host plant interactions. The endosymbiont Candidatus Arsenophonus infects a wide taxonomic range of arthropod hosts, and is suspected of an uncharacterized mutualistic role in hemipterous insects. In the soybean aphid, Aphis glycines, an introduced pest of soybeans in the United States, Arsenophonus is the sole facultative endosymbiont. The focus of this dissertation is to characterize the role of Arsenophonus in the aphid, with an overall emphasis on its impact on aphid management strategies. I first used diagnostic PCR to determine Arsenophonus infection frequency and strain diversity for native and introduced soybean aphids. I found that Arsenophonus infection is a uniform strain that is highly prevalent in soybean aphid. I then determined if Arsenophonus was a defense symbiont by curing two genotypes of soybean aphid of their natural Arsenophonus infection, resulting in infected and uninfected isolines within the same genetic background. I subjected these isolines to assays with three parasitoid species and a common aphid fungal pathogen, Pandora neoaphidis. I did not find differences in parasitism or fungal infections within the treatments. These results indicate that, although Arsenophonus is widespread, the symbiont should not interfere with biological control efforts. I next examined the influence of Arsenophonus on the ability of soybean aphid “biotypes” to colonize resistant Rag plants. I cured three additional soybean aphid biotypes. All isolines were subjected to growth rate assays on resistant Rag versus susceptible soybean. My results indicate that Arsenophonus infected soybean aphids have an increased population growth compared to uninfected aphids regardless of soybean plant type Finally, I induced soybean plants with jasmonic acid (JA) or salicylic acid (SA) to determine the effective plant defense against soybean aphid feeding. I also used Arsenophonus infected and uninfected aphids to determine any interaction between Arsenophonus and plant defense. I found SA treatment decreased soybean aphid population growth for one experiment, but had no effect when replicated. JA treatment had no effect, and there were no interactions between Arsenophonus infection and plant treatments.

Made available in DSpace on 2014-06-11T19:35:00Z (GMT). No. of bitstreams: 0 Previous issue date: 2009-05-15Bitstream added on 2014-06-13T20:45:44Z : No. of bitstreams: 1 rocha_kcg_dr_botfca.pdf: 895303 bytes, checksum: cd87505fac20f9742a811226a9c1fc11 (MD5) / Considerando o aumento de begomovírus e mosca-branca no campo o presente trabalho teve como objetivos a detecção, a caracterização molecular e a análise da diversidade genética de begomovírus em pimentão e tomateiro em diferentes municípios do Estado de São Paulo: Piraju, Tejupá, Santa Cruz do Rio Pardo, São Pedro do Turvo, São Miguel Arcanjo, Itapetininga, Lins, Sabino, Timburí, Iacanga, Pirajuí, Avaí, Reginópolis e Salto; a identificação de biótipos de B. tabaci por meio da amplificação do gene mitocondrial (citocromo oxidase I - mtCOI) seguido de seqüenciamento ou RFLP utilizando a enzima Taq I e a avaliação para resistência de acessos de Capsicum spp. a dois isolados de ToSRV. A análise da variabilidade foi realizada por meio de seqüenciamento da região da capa protéica (DNA-A) com oligonucleotídeos universais e, paralelamente, as mesmas amostras foram testadas por amplificação por círculo rolante (RCA) sendo, posteriormente, clivadas com a enzima de restrição HpaII. Um total de 812 amostras foi analisado, sendo 709 de pimentão e 103 de tomate. Por PCR tradicional, foram detectadas positivas para presença de begomovírus 98 amostras provenientes de pimentão e 39 de tomateiro, e por RCA-PCR, foram 332 e 82 respectivamente, evidenciando maior sensibilidade desta técnica. Dessas amostras, foram seqüenciadas 39 de pimentão e 25 de tomateiro, verificando-se ocorrência prevalente da espécie ToSRV no estado de São Paulo. Infecção mista com ToSRV e ToYVSV foi observada tomateiro. Por RCA-RFLP, foram observados quatro padrões de clivagem com a enzima HpaII e todos foram confirmados como sendo da espécie ToSRV indicando variabilidade molecular intraespecífica. Para tomateiro, foram observados 18 padrões de restrição, dois idênticos aos verificados em plantas de pimentão indicando, possivelmente, infecção pelos mesmos isolados de ToSRV, porém... / Considering the high incidence of begomoviruses and the whitefly on the field, the objetives of this work were to analyze the genetic diversity of begomoviruses infecting pepper and tomato plants in different counties of São Paulo State: Piraju, Tejupá, Santa Cruz do Rio Pardo, São Pedro do Turvo, São Miguel Arcanjo, Itapetininga, Lins, Sabino, Timburí, Iacanga, Pirajuí, Avaí, Reginópolis and Salto; the identification of biotypes of B. tabaci through the amplification of the mitochondrial gene (cytochrome oxidase I) 4 followed by sequencing the gene or analysis by RFLP using the enzyme TaqI and the evaluation of Capsicum spp. for the resistance source for two isolates of ToSRV. The coat protein from the DNA A of the begomovirus was amplified and sequenced, and the same samples were amplified by rolling circle amplification (RCA) followed by analysis by RCA-RFLP using the HpaII enzyme. A total of 812 samples were analyzed, 709 from pepper and 103 from tomato. By PCR, 98 samples from pepper and 39 from tomato were positives for the presence of begomoviruses, while by RCA-PCR 332 and 82 respectively. Thirty-nine samples from pepper and 25 from tomato were sequenced indicating the prevalence of the ToSRV species in São Paulo State. Mixed infections with ToSRV and ToYVSV were found in tomato plants. By RCA-RFLP four restriction profiles were found for ToSRV in pepper plants. In tomato 18 profiles were observed: two identical as observed for ToSRV in pepper, indicating possible infection with the same ToSRV isolates, a profile for ToSRV and ToYVSV mixed infections and also different profiles for ToSRV isolates didn’t found in pepper plants. The sequencing of 17 samples of B. tabaci mitochondrial citochrome oxidase I gene and analysis by Taq I digestion of whiteflies collected in growers areas of pepper and tomato indicated only the presence of the B biotype... (Complete abstract click electronic access below)

Yesinia pestis est l'agent de la peste, maladie infectieuse spontanément mortelle, et une bactérie classée parmi les agents de bioterrorisme de groupe A [http://www.bt.cd.gov/agent/plague]. Les cas sporadiques ont été rapportés dans plusieurs pays d'Asie, d'Afrique, et d'Amérique et la peste reste endémique en Afrique (République Démocratique du Congo; Madagascar) qui déclare le plus grand nombre de cas annuels. La majorité de cas de peste chez les humains et les animaux sauvages se manifeste dans les régions délimitées géographiquement et appelées communément les foyers de la peste. Les mécanismes de la résistance de la peste dans le sol des foyers reste de nos jours un sujet de recherche alors que la peste est maintenant considérée comme une maladie re-émergente. Au cours de notre travail, nous avons développé un outil pour l'identification de Y. pestis par spectrométrie de masse MALDI-TOF MS. Cette méthode s'est avérée très simple et efficace pour l'identification au niveau des espèces, et constitue une méthode de première ligne d'identification. Nous avons ensuite montré que Y. pestis survivait et maintenait sa virulence pendant au moins neuf mois dans le sol stérilisé par la vapeur et humidifié, dépourvu d'éléments nutritifs ajoutés et d'invertébrés du sol. Afin de contribuer à l'étude de l'épidémiologie de la peste, nous avons démontré que seul le biovar Oriantalis est transmis dans un modèle animal par les poux d'homme (Pediculus humanus), les biovars Antiqua et Medievalis de Y. pestis n'étant pas transmissibles par les poux de corps. Le mécanisme impliqué dans la transmission de la peste par les poux de corps reste inconnu, ce qui voudrait dire que le mécanisme de l'adaptation de Y. pestis Orientalis à des nouveaux vecteurs qui sont corrélés aux circonstances de l'épidémie mortelle provoquée par la peste bubonique, reste aussi inconnu. Au cours d'un dernier travail, nous avons étudié des nouveaux composés pour la prophylaxie de la peste. Notamment, nous avons évalué le potentiel du lovastatine dans la prévention de la mortalité pendant la peste. Il a été démontré sur un modèle d'expérimentation avec les souris que la lovastatine réduisait considérablement le taux de mortalité associée à la peste. Toutes les données que nous avons rapportées dans ce rapport de thèse sont destinées à mieux comprendre le cycle épidémiologique de la peste. / Yersinia pestis is the agent of deadly plague and a bacterium listed in the group A of potential bioterrorism agents [http://www.bt.cdc.gov/agent/plague/]. Sporadic cases are reported in several countries in Asia, Africa and America. Majority of human plague cases and enzootic animals occur in the geographical areas of so-called plague foci. The mechanisms sustaining geographical foci of plague remain poorly understood and plague been classified as a currently re-emerging disease. As first step, we established new front line tool for Y. pestis identification by using MALDI-TOF MS. This method was demonstrated to be simple and effective for Y. pestis identification at species level. Second step, we demonstrated that Y. pestis survived fully virulent for at least 9 months in a steam sterilized, humidified soil devoid of any nutritional supplements or any soil invertebrates. In third step we successfully demonstrated that the human louse (Pediculus humanus) as vector of plague and the body lice transmission of plague was restricted to Orientalis biovar; Antiqua and Medievalis biovars of Y. pestis were not able to transmit by body lice. This result shows that a un- explained mechanism is involved in the body lice transmission of plague and Y. pestis Orientalis adaptation to newly described vectors which effectively correlates the mass death caused by bubonic plague in Black Death individuals. Finally we conclude our study by exploring new compounds for the plague prophylaxis. The potential role of lovastatin in the prevention of mortality during plague was assessed. Lovastatin could significantly reduce the mortality associated with plague in an experimental mouse model. All These data herein we reported in our study may help to better understanding the epidemiology of plague.

A major challenge in the treatment of major depressive disorder (MDD) is relapse, which is defined as the return of depressive symptoms during a period of remission. Relapse rates in MDD are high, with approximately 50% of individuals relapsing following treatment of their first depressive episode, therefore early intervention to prevent relapse is crucial. Evidence suggests that immune dysregulation may be linked to longitudinal changes in depressive severity. However, it is currently unknown whether inflammation can predict future relapse in MDD. The objective of this project was to identify potential immune predictors of relapse in participants that responded to a treatment or a combination of treatments for MDD. A secondary objective was to investigate immune composition in efforts to stratify MDD individuals into more homogenous groups and further explore these groups in relation to clinical symptoms. This project is part of the Wellness Monitoring for Major Depressive Disorder longitudinal study (NCT02934334) of responders to antidepressant treatment conducted at 6 clinical sites across Canada. Montgomery Asberg Depression Rating Scale (MADRS) scores were used to assess depression severity and to categorize participants into ultrastable, unstable, and relapse groups. Plasma immune profiles were generated using the LEGENDplex Human Th Cytokine Panel immunoassay. Principal Component Analysis and Kruskal-Wallis tests of individual immune cytokines did not show differences between ultrastable, unstable, or relapse groups. Principal Component Analysis did reveal two cytokine clusters. Hierarchical Clustering analysis identified three distinct immune biotypes characterized by differing levels of Th cytokines and validated the presence of the cytokine clusters. Neither of these outcomes was predictive of relapse in this cohort. Our findings have shown that immune composition may serve as an important factor in parsing heterogeneity that is observed in this disorder through identification of distinct immune biotypes and highly interconnected cytokine subnetworks in major depression. The potential for immune biotypes for optimizing treatment regimens and relapse prevention necessitates further investigation and replication. / Thesis / Master of Science (MSc)

A utilização ampla do glyphosate como herbicida na agricultura brasileira e mundial é conseqüência, dentre outros fatores, de seu custo relativamente baixo, alta eficácia no controle de plantas daninhas, amplo espectro de controle de espécies de plantas daninhas, baixa toxicidade, e curta persistência no ambiente. No entanto, o uso intensivo do glyphosate tem proporcionado a seleção de biótipos de plantas daninhas resistentes a este herbicida, como é o caso da buva (Conyza bonariensis). Apesar de estudos já terem sido conduzidos pela comunidade científica de diversos países, para elucidar o fenômeno sob diversos aspectos, no Brasil são poucos os estudos científicos que esclareçam os mecanismos de resistência de plantas daninhas ao glyphosate. Neste sentido, esta pesquisa teve por objetivo estudar comparativamente populações resistentes (R) e suscetíveis (S) de C. bonariensis ao herbicida glyphosate para caracterizar o nível de resistência das populações R; comparar os níveis de acúmulo de ácido shiquímico entre as populações R e S; elucidar os principais mecanismos de resistência dos biótipos R, através da análise da absorção e translocação do herbicida, determinar a expressão gênica da EPSPS, através de análises semi-quantitativas RTPCR e sugerir alternativas químicas de controle para buva em pomares cítricos do Estado de São Paulo. Os resultados obtidos através do estudo de ácido shiquímico indicaram que o mecanismo de resistência das populações R buva estudadas não está relacionado com insensibilidade da EPSPS ao glyphosate. Já os estudos de translocação diferencial evidenciaram ser esta uma das causas dos mecanismos envolvidos na resistência do biótipo R. Através da análise da expressão gênica observou-se alto grau de similaridade entre seqüências obtidas dos genes EPSPS de C. bonariensis e as seqüências de C. canadensis depositadas no GenBank. Além disso, é possível sugerir que há relação entre a expressão dos genes EPSPS em C. bonariensis e a condição de resistência à ação do herbicida glyphosate em alguns indivíduos dessa espécie de planta daninha. / The extensive use of glyphosate as herbicide in the Brazilian and worldwide agriculture is a consequence, among other factors, of the relatively low cost, high weed control efficacy; wide weed species control spectrum; low toxicity, and short persistence in the environment. However, the intensive use of glyphosate has imposed the selection of certain resistant weed biotypes to this herbicide, such as the case of the weed Conyza bonariensis. Despite the fact that some studies has been developed in some countries around the world, in order to elucidate the phenomenon in several aspects, in Brazil a few studies have been conducted scientifically in order to elucidate the mechanisms of weed resistance to glyphosate. Therefore, this research was developed with the objective of studying the populations of C. bonariensis to characterize the resistance level of populations to glyphosate; compare the levels of shikimic acid accumulation between resistant (R) and susceptible (S) plants; elucidate the main mechanisms of resistance of resistant biotypes to glyphosate, by the absorption and translocation of the herbicide, and determine the EPSPS gene expression, by the RT-PCR semi-quantitative analysis. The results obtained by the shikimic acid study indicated that the mechanism of resistance of the biotype of C. bonariensis studied is not related with insensitivity of the EPSPS to glyphosate. On the other hand, the differential translocation maybe considered as one of the mechanisms involved in the resistance of the biotype R of C. bonariensis. With regards to gene expression, it was observed high degree of similarity among the sequences obtained of the EPSPS gene of C. canadensis, and the sequences of C. canadensis deposited in the GenBank. Furthermore, it is possible to suggest that there is relation between the gene expression in C. bonariensis and the resistance condition to the action of the herbicide glyphosate in some individuals of this weed specie.