The theory and the practical application of the simulation of root infection of winter wheat by the take-all fungus, <i>Gaeumannomyces graminis</i> var. <i>tritici</i>, are critically evaluated with respect to field epidemics and to infection of seedlings within controlled environments. Several simple models for disease progress in field epidemics are evaluated with respect to field data, including a generalized logistic equation and systems of simple non-linear differential equations, with and without algebraic solutions. An investigation is made of disease heterogeneity in the field and transect data derived from sampling 11,000 plants are analysed for the presence of significant pattern. The effect of the observed spatial heterogeneity on the precision of field data is also empirically investigated. The use of a controlled-environment experiment to model the effect of volunteer infestation on inoculum survival in the field is demonstrated, and a simple model is used to quantitatively estimate the effect of volunteer infestation on inoculum multiplication. Data for a seedling disease epidemic are simulated by three mathematically and computationally diverse simulators derived from a single underlying theoretical model. The first is a complex simulator written in FORTRAN and run on a mainframe computer which resolves the infection process into a number of detailed submodels. The second simulator is written in BBCBASIC and 6502 machine code and makes use of a discrete root map to hold information on host growth and infection. In the third simulator the model is expressed as a series of rate equations and is run on a simulation package on the BBC microcomputer. The simulation techniques used are discussed and evaluated with respect to model development and the descriptive accuracy of the simulators. In conclusion a strategy is proposed for the development of a comprehensive model for field epidemics of take-all by means of controlled-environment experimentation.

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Thesis (Ph. D.)--University of Wisconsin--Madison, 1963. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 55-58).

Chemical and biological aspects of thiarubrine, a highly antifungal dithiacyclohexadiene polyine, were investigated. A tissue culture system for the production of thiarubrines was developed by culturing hairy roots of Chaenactis douglasii induced by Agrobacterium rhizogenes strain TR7. One culture line accumulated two times the levels of thiarubrines of nontransformed control root cultures, while maintaining rapid growth. The combination of fast growth and high thiarubrine accumulation could not be duplicated in controls by adding exogenous NAA to the culture medium. Hairy root cultures also produced less thiarubrine B relative to thiarubrine A compared to controls. Thiarubrine synthesis appears to be closely correlated with degree of tissue differentiation; it is suggested that it may be more practical to improve the growth rate of thiarubrine-producing root cultures by transformation rather than seek to induce synthesis in fast-growing suspension cultures. The biosynthetic relation between thiarubrines and the always co-occurring thiophenes was investigated by performing ³⁵S tracer experiments with C. douglasii hairy root cultures. It is possible that the thiophenes are not actively synthesized by the roots but rather are products of thiarubrine decomposition resulting from the extraction procedures and other manipulations of the cultures. The in vitro conversion of thiarubrine to thiophene can be induced by light, heat and other agents. No turnover of thiarubrines could be detected in the cultures in late logarithmic or stationary phases of the growth cycle. I Thiarubrines show strong light-independent antibacterial and antifungal activity. The mechanism of action of thiarubrine against E. coli and S. cerevisiae was investigated using comparative disk bioassays. A very similiar polyine from Rudbeckia hirta was as active as thiarubrine in the dark, indicating the central role of the disulfide ring in toxicity of the compounds. Visible light enhanced this activity suggesting that decomposition of the disulfide ring is important for its antibiotic effects. The photodegradation product, a thiophene, is phototoxic, probably via both type I and type II photosensitization mechanisms. The root culture extracts of Rudbeckia hirta yielded a new isomer of a known dithiacyclohexadiene polyine. MS and NMR analyses confirmed the cis configuration of this isomer. / Science, Faculty of / Botany, Department of / Graduate

Thesis (Ph. D.)--University of Wisconsin--Madison, 1935. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 34-37).

Relationships between jack pine dwarf mistletoe (Arceuthobium americanum Nutt. ex Engelm.) and Armillaria root disease (Armillaria ostoyae (Romagn.) Herink) were examined to determine how these two disease agents contribute to jack pine (Pinus banksiana Lamb.) decline and mortality in the Belair Provincial Forest, Manitoba, Canada. The incidence and extent of Armillaria root disease was strongly related to tree vigor. Dwarf mistletoe infection did not affect either the incidence of Armillaria or the mean percentage of root system colonization within vigorous, declining, and dead classes of trees. However, field observations and other analyses indicate that dwarf mistletoe was primary responsible for jack pine decline and mortality. In dwarf mistletoe mortality centers, Armillaria appeared to act opportunistically, extensively colonizing only the stressed trees. Analysis of distributions of percent Armillaria colonization revealed that rapid root system colonization occurred just prior to, or at the time of tree death.

Submitted by (lucia.rodrigues@ufrpe.br) on 2017-03-20T14:48:52Z No. of bitstreams: 1 Litervaldo Pereira Machado.pdf: 826962 bytes, checksum: 4c267bd8c50631dcb8bdf8b7b2c1cc47 (MD5) / Made available in DSpace on 2017-03-20T14:48:52Z (GMT). No. of bitstreams: 1 Litervaldo Pereira Machado.pdf: 826962 bytes, checksum: 4c267bd8c50631dcb8bdf8b7b2c1cc47 (MD5) Previous issue date: 2012-02-29 / Rhizoctonia canker, caused by Rhizoctonia solani, is an important cowpea disease in Northeastern region of Brazil. This thesis aimed: a) to evaluate the potential of crop rotation and green manures in inducing suppressiveness to Rhizoctonia canker in cowpea; b) to identify the biotic factors related to suppression; and c) to analysis the stability of the disease suppression by selected crop rotation in relation to different isolates and inoculum density of the pathogen, and soils from different locations. The experiments were conducted in microplots in the field. In relation to crop rotations, Initially, 14 treatments were compared in four growing seasons, including different combinations of cowpea (CA) in rotation with cotton (AL), sunflower (AL), castor bean (MA), corn (MI) and sorghum (SO), and in combination with fallow (PO) and cowpea monoculture. The rotations CA-MI-SO-CA, CA-GI-SO-CA and CA-MI-PO-CA provided reductions of 77.6%, 74.0% and 73.9% in the disease severity, respectively. When the stability of disease control by CA-MI-SO-CA rotation was evaluated in relation to different pathogen isolates, inoculum densities and soils, in all situations the disease severity was significantly (P0,0001) lower under crop rotation as compared to cowpea monoculture, indicating the potential of the crop rotation for controlling the Rhizoctonia canker. In relation to green manures, 13 treatments were compared in five growing seasons, considering different combinations of cowpea and green manures (sunn hemp, breviflora crotalaria, showy crotalaria, jack bean, velvet bean, dwarf mucuna, lablab bean, dwarf pigeon pea, forage pigeon pea, corn, millet and sorghum). For the two evaluations after green manures cultivation, the incorporation of sorghum into the soil led to smallest levels of severity of cowpea Rhizoctonia canker, reducing by 81.3% and 83.3% the disease severity. There was no significant correlation from levels of disease severity with microbiological variables. / A rizoctoniose, causada por Rhizoctonia solani, é uma importante doença do feijão-caupi na região Nordeste do Brasil. Essa tese teve como objetivos: a) avaliar o potencial da utilização de rotações de culturas e adubos verdes na indução da supressividade à rizoctoniose do feijão-caupi; b) identificar os possíveis fatores bióticos dos solos responsáveis pela supressividade; e c) analisar a estabilidade do controle pela rotação de cultura selecionada em relação a diferentes isolados e densidades de inóculo do patógeno, bem como solos de diferentes localidades. Os experimentos foram realizados em microparcelas no campo. Em relação à rotação de culturas, inicialmente foram comparados 14 tratamentos em quatro ciclos de cultivo, incluindo diferentes combinações de feijão-caupi (CA) em rotação com as culturas de algodão (AL), girassol (GI), mamona (MA), milho (MI) e sorgo (SO), bem como em combinação com pousio (PO) e feijão-caupi em monocultura. As rotações CA-MI-SO-CA, CA-GI-SO-CA e CA-MI-PO-CA propiciaram reduções na severidade da doença de 77,6%, 74,0% e 73,9%, respectivamente. Quando avaliada a estabilidade do controle da doença pela rotação CA-MI-SO-CA a diferentes isolados, densidades de inóculo e solos, em todas as situações a severidade foi significativamente inferior (P0,0001) sob a rotação de culturas comparada à monocultura, indicando o potencial de utilização da rotação no controle da rizoctoniose. Em relação aos adubos verdes, foram comparados 13 tratamentos, considerando diferentes combinações de feijão-caupi e adubos verdes (crotalária breviflora, crotalária juncea, crotalária spectabilis, feijão-de-porco, guandu anão, guandu forrageiro, labe-labe, mucuna anã, mucuna preta, milho e sorgo), em cinco ciclos de cultivo. Nas duas avaliações realizadas após o cultivo de adubos verdes, a incorporação de sorgo ao solo propiciou os maiores níveis de controle da doença, reduzindo em 81,3% e 83,3% a severidade. Não houve correlação significativa dos níveis de severidade da rizoctoniose com as variáveis microbiológicas avaliadas nos solos.

We conducted an experimental evaluation of treatments to limit Heterobasidion occidentale infection of white fir (Abies concolor) stumps and wounds in California mixed conifer forests. We tested the efficacy of urea, borate, and a mixture of two locally collected Phlebiopsis gigantea strains in preventing pathogen colonization of fir stumps and separately, urea and borate as infection controls on experimental stem wounds. These were paired with a laboratory test on ~100 g wood blocks with and without a one-week delay between inoculation and treatment. Urea, borates, and Phlebiopsis treatments all significantly reduced the stump surface area that was colonized by H. occidentale at 84%, 91%, and 68%, respectively, relative to the controls. However, only the borate treatments significantly lowered the number of stumps that were infected by the pathogen. The laboratory study matched the patterns that were found in the stump experiment with a reduced area of colonization for urea, borates, or P. gigantea treatments relative to the controls; delaying the treatment did not affect efficacy. The field wound experiment did not result in any Heterobasidion colonization, even in positive control treatments, rendering the experiment uninformative. Our study suggests treatments that are known to limit Heterobasidion establishment on pine or spruce stumps elsewhere in the world may also be effective on true firs in California.

The involvement of pectin and pectinases in the host pathogen interaction of P. terrestris and Allium cepa were investigated by use of pectin histochemical stains at the electron microscope level. Several different pectin histochemical stains were used, but only two (the hydroxylamine reaction, and the pectin stain developed in this study) gave reliable results. It was observed that by the time the fungus has reached the host cell wall pectinesterase and endoplygalacturonase have fully removed the pectin from the host cell wall. When this has occurred, cellulases are released which continue to degrade the host cell wall. Electron transparent areas appeared where there were no COOH groups.