Thesis (M.Sc.)(Microbiology)--University of Pretoria, 2005. / Title from opening screen (viewed March 28, 2006). Includes summary. Includes bibliographical references.

Cotton (Gossypium hirsutum) growth, development, and yield can be limited due to reniform nematode and bacterial blight infestation. Studies were conducted in 2016 and 2017 to evaluate the profitability of a soil fumigant application, seed treatments, and inurrow nematicides to protect cotton from nematode infestation as well as inoculation of bacterial blight at various growth stages in cotton to determine effects on yield. Research was conducted by applying various combinations of nematicides to cottonseed at planting and a fumigant prior to planting. Bacterial blight was conducted by inoculated on cotton at multiple growth stages throughout the year. Based on the results of these studies, a seed treatment plus inurrow application should be applied at planting in nematode infested fields to increase yield and economic returns in cotton. Bacterial blight infestation was greatest when inoculated at pinhead square in cotton.

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Copies of author's previously published articles inserted. Bibliography :leaves 65-80 Ice nucleation active (INA) bacteria were detected in a pea field in South Australia. They were identified as strains of Pseudomonas syringae and Pseudomonas flourescens biotype 1. Some chemical agents were tested on the two ice nucleating species, as cryoprotectants.

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Copies of author's previously published articles inserted. / Bibliography :leaves 65-80 / x, 80, [64] leaves, [24] leaves of plates : ill. (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Ice nucleation active (INA) bacteria were detected in a pea field in South Australia. They were identified as strains of Pseudomonas syringae and Pseudomonas flourescens biotype 1. Some chemical agents were tested on the two ice nucleating species, as cryoprotectants. / Thesis (Ph.D.)--University of Adelaide, Dept. of Crop Protection, 1991

Thesis (Ph. D.)--University of Adelaide, Dept. of Crop Protection, 1991. / Copies of author's previously published articles inserted. Includes bibliographical references (leaves 65-80).

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Doctor of Philosophy / Department of Plant Pathology / Frank F. White / Plants have evolved sophisticated mechanisms to protect against microbial invaders of which resistance (R) genes are an important component. R genes mediate specific recognition of pathogens possessing cognate avirulence (avr) gene products, which leads to the induction of plant defense responses and the arrest of pathogen ingress. In contrast to numerous examples of R gene–avr interactions, the susceptible interaction is less well examined. Recent studies on rice and wheat indicate that host resistance to pathogens also involves genetic variability in dominant traits for susceptibility. Xanthomonas oryzae pv.oryzae (Xoo) causes bacterial blight disease in rice, a serious threat in the major rice growing regions of Asia. The pathogenicity of Xoo depends on the translocation of a cocktail of effector proteins into rice cells by a type III secretion system. The family of transcription activator like (TAL) effectors is the one of the most intriguing due to their eukaryotic features and function as major virulence determinants. The specificity of TAL effectors is determined by the nearly identical repeat units at the center of each protein. The major virulence determinant of the strain PXO99A is PthXo1, which hijacks the transcription of the host susceptibility (S) gene Os8N3, an allele of recessive resistance gene xa13. The strains that overcome xa13-mediated resistance harbor alternate major TAL effectors including PthXo2, PthXo3 and AvrXa7. Alternate effectors do not induce Os8N3. This study identified the alternate S gene Os11N3, which is dependent on the effectors AvrXa7 and PthXo3. The effectors bind to specific elements in the proximal promoter regions of the respective S genes and act as transcriptional activators. Our results indicate that rice–Xoo interactions involve gene-for-gene susceptibility to bacterial blight in addition to gene-for-gene resistance.

Um dos principais fatores limitantes da produção de algodão é a ocorrência de doenças e, entre os patógenos mais importantes estão às bactérias, que causam danos significativos à cultura. A doença conhecida como mancha angular, causada pela bactéria Xanthomonas axonopodis pv. malvacearum (Xam), é uma doença grave, que tem gerado grande preocupação dos produtores. Porém, muitos cultivares com boas características agronômicas apresentam suscetibilidade ao patógeno e, poucos são aqueles que apresentam resistência à doença. O controle da mancha angular é realizado basicamente com uso de resistência genética ao patógeno. Uma das principais fontes de inóculo para esta bactéria é a semente infectada. Este trabalho objetivou o desenvolvimento de um meio semi-seletivo para o isolamento de Xam em sementes de algodão, visando a utilização em análises de rotina em laboratórios de patologia de sementes. O meio de cultura semi-seletivo possuí a seguinte constituição: 3 g de extrato de carne; 5 g de peptona; 10 g de amido solúvel; 10 mL de Tween 80; 0,25 g de cloreto de cálcio; 150 µL de solução de cristal violeta a 1%; 50 mg de cefalexina; 10 mg de clorothalonil; 10 mg de tiofanato metílico e água destilada por 1000 mL. Este meio de cultura possui baixa repressividade a Xam e permite isolar este patógeno de sementes de algodão. / One of the main limiting factors of the cotton production is the occurrence of diseases. The bacteria are among the most important pathogens causing significant losses in the production. Cotton bacterial blight is caused by the bacterium Xanthomonas axonopodis pv. malvacearum (Xam). Is a serious disease that affects cotton and has worried world producers. The main source of inoculum for this bacterium is the infected seed. This work had as objective the development of a semi-selective medium to detect Xanthomonas axonopodis pv malvacearum in cotton seeds for routine tests in seed pathology laboratories. By fungitoxicity tests, basead on qualitative and quantitative antibiograms, it was idealized a semi-selective medium with the folloing composition: peptone (5.0 g/L); agar (15.0 g/L); meat extract (3.0 g); starch (10.0 g/L); violet crystal (150.0 µL violet crystal solution at 1%); water (1,000 mL); CaCl2 (0.25 g); Tween 80 (10.0 mL/L). This medium has small effect on Xam and allows to isolate cotton seeds pathogens.