No description available.

Thesis (M. Sc.(Plant Pathology))--University of Pretoria, 2006. / Includes bibliographical references. Available on the Internet via the World Wide Web.

The Ellensburg Formation, preserved in the Nile basin 50 km northwest of Yakima, Washington, consists of a series of middle to late Miocene epiclastic and pyroclastic rock assemblages rich in porphyritic hornblende-biotite dacite. Geochemical, petrographic, and stratigraphic correlations indicate that Old Scab Mountain, a dacite porphyry intrusion, located at the western margin of the basin (lat. 46°53'30", long. 121°13'00"), is the probable source for much of the upper Ellensburg volcaniclastic material in the basin. The dacite intrusion exposed at Old Scab Mountain was emplaced at depths of 1 to 3 km and underlaid a now eroded volcanic edifice. This volcanic center is interpreted to have been active during the time of deposition of the upper Ellensburg Formation. AK-Ar age of 8.75 ± 0.20 Ma for an adjacent sill of similar dacite suggests an age for Old Scab Mountain between 9 to 7 Ma (Smith, 1988a). This age corresponds with the upper Ellensburg Formation which stratigraphically overlies Grande Ronde Basalt lava flows of the Columbia River Basalt Group, within the basin. Stratigraphic reconstruction of the Nile basin deposits indicates a dome collapse eruptive style. Progressive dome growth was punctuated by short-lived eruptions resulting in dome collapse and deposition of debris-avalanche and lahar deposits. These deposits were remobilized by fluvial processes which generated thick conglomerates and interstratified volcanic sandstones. Upper Ellensburg deposits and dacite of Old Scab Mountain are calc-alkaline and medium-K in composition. Silica content ranges from 53 to 67 weight percent Si02 for upper Ellensburg deposits and 66 to 67 weight percent Si02 for dacite of Old Scab Mountain. Older deposits composing the lower Ellensburg Formation are interbedded with and underlie the Grande Ronde Basalt. The lower Ellensburg deposits are typically more tholeiitic, range from 56 to 74 weight percent Si02 , and show slightly higher trace element concentrations than the upper Ellensburg deposits. These deposits were possibly derived from other dacite centers located near the headwaters of the adjacent Naches basin.

Psoroptes ovis mites are the causative parasites of sheep scab disease. It is a contagious disease which causes intense pruritus, wool loss and the development of lesions. These lesions are exacerbated by secondary bacterial infections. Bacteria appear to play an integrated role in the pathogenicity of this disease and are found in the internal cavities of P. ovis. The aim of this study was to investigate these bacterial associations, with the aim of identifying a microbial target for sheep scab control. The microbial communities associated with sheep scab were investigated using both molecular and bacteriological techniques. Several environmental niches were targeted: scab-infected fleece, internal mite cavity and excreted faecal trails. Microbial communities were very complex, with a variety of species and bacterial groups identified. Some bacteria were common to all environments, whereas others were isolated from one sample. Both natural and in vivo cultured mites were investigated in an attempt to identify universal and potentially beneficial bacteria. In addition, P. ovis mites were screened using PCR to detect potential endosymbiotic bacteria. Positive identification was made of Comamonas sp. in both natural and in vivo cultured mites; this species has been identified as an endosymbiont in other arthropods and its role in P. ovis requires further investigation. In vitro feeding experiments were carried out with P. ovis mites in the laboratory. Initially mite chambers were constructed and optimised to encourage maintenance of P. ovis off-host. A number of diets were tested and antibiotics were compared for their effect on bacteria within P. ovis. In vitro experiments revealed that P. ovis survival was significantly reduced with the administration of antibiotics and there was also evidence that they altered internal bacterial densities. The potential of bacteriophage therapy for the microbial control of bacteria associated with P. ovis was investigated. Bacteria isolated from P. ovis faecal trails were used to isolate bacteriophage from environmental samples. Sixteen bacteriophage were successfully isolated, which were infective against three mite faecal bacteria. Isolated bacteriophage were characterised by a number of methods including their response to chemicals, enzyme and infection dynamics in both solid and liquid phases. In vitro experiments with bacteriophage were also investigated, resulting in a significantly reduced mite lifespan seen with some bacteriophage lysates. The potential for using bacteriophage for the control of P. ovis mites is discussed.

No description available.

The root system is a vital and dynamic part of a plant throughout its lifetime. Its spatial distribution is the consequence of multiple interactions with the surrounding soil medium. In particular, the presence of pathogens in soil may influence the development of the plant, especially the below-ground part, in both its physiology and its structure. Studies of diseased plant roots may take different approaches and investigate disease effects at different levels. In this study, two groups of four potato (Solanum tuberosum L.) plants were grown in middle-sized plastic pots in a greenhouse, and their root systems, together with the soil medium (i.e., sieved and autoclaved homogeneous sand), were submitted to computed tomography (CT) scanning every two weeks until 10 weeks after planting. For the "diseased" group, sand was inoculated with Streptomyces scabies EF-35, the causal agent of potato common scab, at the time of planting. Disease effects on tissue density of roots and below-ground organs, space occupancy and complexity were assessed by analyzing the CT scanning data in the spatio-temporal approach. Fluctuations of tissue density over time were different, on average, between the two groups. They were characterized by an increase of density in Week 2 for the diseased group, reflecting a hardening of tissue, and a delayed decrease relative to the "healthy" group, suggesting a slower transfer of energy from the seed potato to growing roots. Space occupancy, which was studied via volumetric growth rates evaluated from CT scan data, and complexity, which was quantified by the fractal dimension estimated from skeletonized 3-D images constructed from CT scan data, also showed differences in the first part of the experiment. Original analytical procedures based on data transformation and curve fitting in histogram analysis of CT numbers were developed to obtain those results. In conclusion, the new approach presented here, which is based on the advanced processing of CT scanning data collected over time on developing plant root systems and below-ground organs, can be recommended for future phytopathological applications.

The aim of the thesis was focused on assessing the significance of the impact of habitat on the occurrence of the common scab of potatoes. In this context, following factors were evaluated: degree and extent of infestation tubers with common scab, effect of the habitat, impact of the variety, vintage influence, the influence of fertilization with nitrogen and sulfur influence seed treatment, starch content, tuber yield, the proportion of tubers over 40 mm. The review of literature of thesis includes chapters regarding the origin of potato, potato and morphological characteristics of its growth, consumer potatoes and factors that affect the quality and yield. It mentions measures against diseases and pests. The last section is devoted to common scab of potato. The practical part deals with evaluating the impact of habitat on the incidence of common scab of potatoes. The attempt was based on the habitat with the occurrence of common scab and habitats without occurrence of common scab in Vyklantice. The results were processed in program Statistica, version 12.0. (StatSoft) function of multifactor and one-way analysis of variance (ANOVA). At the habitat with higher pH and KVK higher incidence of common scab was recorded. It confirmed the impact of resistance of variety on the incidence of common scab. It was not confirmed statistically significant dependence on fertilizer nitrogen fertilizer LAV and seed treatment tubers with Trichoderma strains. It confirmed a statistically significant dependence on the incidence of common scab on fertilization with SulfoGranulat.

Resumo: Este trabalho teve por objetivos: (i) selecionar genótipos de tangerinas resistentes a infecção por Alternaria alternata, e estabelecer relações entre níveis de severidade da doença entre folhas e frutos, (ii) avaliar a contribuição de metabólitos na resistência de folhas maduras de tangerinas a A. alternata, (iii) selecionar genótipos de tangerina resistentes a infecção por Elsinoe fawcettii. Para tais experimentos foram utilizados 22 genótipos de tangerina pertencentes ao banco de germoplasma da Estação experimental de Citricultura de Bebedouro, Bebedouro-SP. (i) Dentre os materiais genéticos resistentes, foram constatados quatro genótipos de clementinas (Citrus clementina), seis mandarinas, sendo duas pertencentes a C. reticulata, duas a C. tangerina, uma a C. deliciosa e uma a C. nobilis; um tangelo (C. tangerina x C. paradisi); dois híbridos de mandarinas, sendo um resultante do cruzamento entre C. nobilis x C. deliciosa, e o outro de C. clementina x C. reticulata; um híbrido de tangor (C. clementina x C. sinensis) e dois híbridos de satsumas (C. unshiu x C. deliciosa.). Também foi constatado indícios de relação entre severidade de doença em folhas jovens destacadas e incidência natural de doença em frutos. (ii) Ao final dos experimentos, não foi observado influência desses metabólitos na defesa das folhas maduras de tangerina a MMA. (iii) Dente os genótipos avaliados, foram observados 10 materiais genéticos resistentes a verrugose. Dentre estes materiais, observou-se que os genótipos Commune, Caffin, Bruno, Burgess, Peau Lisse, Zanzibar, Beuty of Glen Retreat, Rode King e Encore também se apresentaram resistentes a MMA. Estes materiais são promissores para o cultivo de tangerinas em áreas de ocorrência destas doenças, e poderão contribuir com futuros trabalhos de melhoramento genético para resistência a MMA e verrugose. / Abstract: The aims of this work were: (i) select tangerine genotypes resistant to Alternaria alternata infection and classify relative degrees of disease severity among leaves and fruits, in order to ultimately control the pathogen; (ii) evaluate metabolites contribuition on mature leaves of tangerines to A. alternata; (iii) select tangerine genotypes resistant to Elsinoe fawcettii. For such experiments 22 tangerines genotypes from germoplasm bank at Estação experimental de Citricultura de Bebedouro, Bebedouro-SP were used. (i) Among the resistant genetic materials, four clementines genotypes (Citrus clementina), six mandarines, being two of C. reticulata, two C. tangerina, one C. deliciosa and one C. nobilis; one tangelo (C. tangerina x C. paradisi); two mandarines hybrids, being one resulted between C. nobilis x C. deliciosa crossing, and other at C. clementina x C. reticulata; one tangor hybrid (C. clementina x C. sinensis) and two satsumas hybrids (C. unshiu x C. deliciosa) were found. A consistent relationship was noted among level of susceptibility in leaves (as evaluated following either natural infection or artificial inoculation), severity and susceptibility of fruit, suggesting a new methodology for diagnosis, identification and selection of Citrus spp. varieties resistant to A. alternata. (ii) At the end of experiments, it was not found any relationship between the presence of these metabolites and resistance to MMA on tangerines mature leaves. (iii) Among the genotypes evaluated, 10 genetic materials resistant to scab were observed. Finally, Commune, Caffin, Bruno, Burgess, Peau Lisse, Zanzibar, Beuty of Glen Retreat, Rode King and Encore cultivars, being resistant to A. alternata and also to E. fawcettii, exhibited good agronomic characteristics and, consequently, show a promising economic exploration. / Orientador: Antonio de Goes / Coorientador: Eduardo Sanches Stuchi / Banca: Antonio Baldo Geraldo Martins / Banca: Sérgio Florentino Pascholati / Mestre

Ensyeh Sarikhani Soil microbial communities in agroecosystems and natural habitats contributing to resistance and resilience of the soil environment. Summary The control of common scab of potatoes (CS) includes resistant varieties (cultivars), precise fertilization, increase of soil moisture, and chemical treatments. Yet, these management practices do not have common or reproducible results at differing sites. A monitoring study was done in 32 sites to evaluate the relation between CS and biological/chemical soil parameters. Correlations were observed between scab severity and content of nutrients such as Fe, N, and Ca in soil and periderm, and between disease severity and abundance of actinobacteria and total bacteria, together with the pathogenicity determinant, txtB gene (biosynthetic gene of thaxtomin) in both soil and periderm of potatoes. The findings led to novel conclusions, which can help to understand relationships applicable in scab control. Peat and DTPA chelated iron were supplemented to pots filled with soil conducive for CS in order to determine the effects of soil organic matter, iron and pH on CS development. The results were compared with data obtained for a suppressive soil from a nearby field with naturally low CS severity. Both peat and iron supplements decreased CS and the combination...

Fusarium graminearum (Schwabe), causal organism of fusarium head blight (FHB), has become a major pathogen of wheat (Triticum aestivum L.) throughout North America. Since its discovery in the United States, the disease has spread south and east until at present it is an annual threat for growers of winter wheat in the Mid-Atlantic region. Yield losses for soft red winter (SRW) wheat averaged 908 kg ha-1 in the FHB outbreak of 1998 (Griffey et al., 1999). The economic loss from this single FHB epidemic was an estimated 8.5 million dollars. Environmental conditions favorable for FHB development, including above average rainfall and temperatures during anthesis, have become more common in the Upper-Midwestern wheat-growing region over the past decade, leading to substantial losses in wheat and barley crops. This, coupled with low prices being paid for wheat, has prompted research toward solving the problem of FHB across the nation. The majority of labor and financial resources devoted to FHB research are dedicated to incorporating FHB resistance into adapted wheat lines. While this is a prudent method of combating this disease, this process will take many years to complete. We have examined all FHB assessment parameters, which include FHB incidence, FHB severity, FHB index, percentage fusarium damaged kernels (percentage FDK), and 15-acetyl deoxynivalenol toxin (DON toxin) accumulation, to ascertain which assessment parameters best quantify FHB resistance levels in addition to grain yield and grain volume weight (GVW) losses. FHB index provides the most reliable in-field assessment of a genotype's resistance level, whereas percentage FDK provides a reliable measure of a genotype's resistance level post-harvest. FHB index and percentage FDK are also the most predictive assessment parameters with regard to grain yield and GVW loss. A wide range in both level and type of resistance was observed among genotypes examined in this study. The cultivars Agripro Patton, Ernie, INW9824, Roane, and the experimental line NY87048W-7388 consistently had lower scores for FHB assessment parameters and lower losses of grain yield and GVW. / Master of Science