Thesis (Ph. D.)--University of Wyoming, 2007. / Title from PDF title page (viewed on Nov. 7, 2008). Includes bibliographical references (p. 86-88).

Thesis (M.Sc.)--Memorial University of Newfoundland, 1997. / Bibliography: leaves 74-83.

Thesis (M.A.)--Catholic Theological Union, 1978. / Includes bibliographical references (leaves 110-111).

This doctoral thesis presents three original research papers investigating aspects of agricultural production in small-farming households in two regions of Ethiopia. While answering specific research questions, the articles are connected and motivated by an interest in essential themes of agricultural development: access to seed, the use and conservation of agrobiodiversity as well as strategies to manage production risk in smallholder agriculture. The first article analyses patterns of agrobiodiversity in three communities with comparatively favourable farming conditions and good market access in the East Shewa zone of Eastern Ethiopia. Using original panel data of more than 300 households collected in 2011 and 2013, the study shows that the least vulnerable households grow a larger portfolio of food crops and wheat varieties. Based on these findings, the role of agrobiodiversity for ex ante risk management and alternative incentives for portfolio diversification are discussed. The second article investigates the effects of a fungal crop disease on agricultural production of households in East Shewa using household level panel data during and after an epidemic outbreak of yellow rust in 2010/11. Findings suggest that while varietal diversity in wheat does not increase, roughly thirty percent of households make changes in their varietal portfolio and reduce wheat cultivation in response to the disease. Disease resistant varieties are only available to 16 percent of all households with preferential access to agricultural resources. The third article presents a mixed methods study of a highly developed informal seed insurance network among subsistence‐oriented small farmers in two communities in the West Hararghe zone of Ethiopia. Based on a survey and interviews with 150 farmers, we find that the vast majority of small farmers actively participate in informal seed assistance by giving or receiving small quantities of seed without compensation. We argue that the seed assistance through gifts is practiced to insure against hunger ex ante and facilitate access to crop genetic resources in a centre of crop origin and diversity.

Master of Science / Department of Plant Pathology / William Bockus / Robert Bowden / Stem rust, caused by the fungus Puccinia graminis f. sp. tritici, has historically been one of the most important diseases of wheat. Although losses have been much reduced in the last fifty years, new highly virulent races of the pathogen have recently emerged in East Africa. These new races are virulent on nearly all of the currently deployed resistance genes and therefore pose a serious threat to global wheat production. The spring wheat variety ‘Kingbird’ is thought to contain multiple quantitative trait loci (QTLs) that provide durable, adult-plant resistance against wheat stem rust. Stem rust-susceptible Kansas winter wheat line ‘KS05HW14’ was backcrossed to Kingbird and 379 recombinant lines were advanced to BC₁F₅ and then increased for testing. The lines were screened for stem rust resistance in the greenhouse and field in Kansas and in the field in Kenya over multiple years. We identified 16,237 single nucleotide polymorphisms (SNPs) with the Wheat 90K iSelect SNP Chip assay. After filtering for marker quality, linkage maps were constructed for each wheat chromosome. Composite interval mapping and multiple-QTL mapping identified seven QTLs on chromosome arms 2BL, 2DS, 3BS, 3BSc, 5DL, 7BL, and 7DS. Six QTLs were inherited from Kingbird and one QTL on 7BL was inherited from KS05HW14. The location of the QTL on 2BL is approximately at locus Sr9, 3BS is at Sr2, 3BSc is at Sr12, and 7DS is at Lr34/Yr18/Sr57. Although no QTL was found on 1BL, the presence of resistance gene Lr46/Yr29/Sr58 on 1BL in both parents was indicated by the gene-specific marker csLV46. QTLs on 2DS and 5DL may be related to photoperiod or vernalization genes. Pairwise interactions were only observed with race QFCSC, most notably occurring with QTLs 2BL and 3BSc. These results confirm that there are multiple QTLs present in Kingbird. Ultimately, the identification of the QTLs that make Kingbird resistant will aid in the understanding of durable, non-race-specific resistance to stem rust of wheat.

Ramets of 14 clones of western black cottonwood Populus trichocarpa Torr. & Gray collected from the interior and coast of British Columbia were tested in the nursery for their growth performance after infection by the leaf rust Melampsora occidentalis Jacks. Linear relationships were demonstrated between various growth parameters (total dry weight, stem dry weight, root dry weight, volume, diameter and height) and disease severity rated as diseased leaf-weeks divided by total leaf-weeks. Losses due to rust infection included reduced total dry weight and volume growth in the year of heavy disease, the death of severely infected ramets during the following winter and reduced initial volume increment in the following growing season. The percentage reduction in yield (total dry weight) was greater than the cumulative percent leaf area infected, suggesting that the rust infected leaf parts act as sinks for photosynthate. The normal pattern of photosynthate allocation was altered in favour of the top growth of ramets. Ratios of stem/root dry weight increased rapidly as disease level increased. A threshold infection level, below which no loss occurred, was not detected in this pathosystem. Significant variation in rust resistance of black cottonwood clones was detected both within and between the two geographic areas. Clones from the coast or warm, moist areas were, on average, more resistant than clones from the interior or cold, dry climates. The phenomenon of induced resistance was not detected at either the local or the systemic levels in black cottonwood challenged by the rust. Variation in rust tolerance among black cottonwood clones was demonstrated. Rust tolerance was defined as the slope of the relationship between yield of ramets (expressed as a proportion of controls) and disease severity (expressed as the proportion of the total number of leaf-weeks infected). A negative correlation between rust tolerance and rust resistance was found. In the collection of clones tested, the positive effect of disease resistance on the growth of cottonwood clones was partially counterbalanced by the negative effect of reduced tolerance on the growth. The importance of this relationship in both natural and artificial selection of superior trees against disease is indicated. / Forestry, Faculty of / Graduate

A major concern in contemporary ecology has been the failure of management in many economically and socially important renewable resource systems. In spite of efforts to the contrary, management has often witnessed the evolution of such systems into behavior patterns almost diametrically opposed to their original objectives. Actually, it is management intervention which often seems to have initiated this evolution by disturbing the system's stability properties. This study shows how an alternative approach which emphasizes system redesign may alleviate the .problem of changing stability properties in some relatively simple and well studied ecosystems: the cereal rusts and the crops which they attack. The plant disease epidemiological literature records a number, of ideas about the behavior and management of cereal rust systems. Many of these ideas have been neither adequately field tested nor developed in a coherent analytic framework. In this study mathematical methods are used to determine the logical consequences of some of these hypotheses. The analysis suggests that cereal rust systems might indeed be redesigned to help management meet its objectives. Four alternative and mutually compatible potential strategies for achieving this goal are considered: (1) using natural enemies to delay disease onset, (2) using multilines or variety mixtures to inhibit plant to plant dispersal, (3) changing field geometry to increase dispersal wastage, and (4) employing polygenic resistance to slow the growth rate of the best adapted races. The research and development required to implement any of these strategies is briefly discussed. Recommendations for future work and comments on the promise of plant epidemiology as an area for ecological research are provided. / Science, Faculty of / Zoology, Department of / Graduate

The possible biochemical mechanisms of varietal and species specificity of obligate fungal parasites are considered in relation to the established genetics and biochemistry of host-parasite systems. The two general theories of specificity which have been put forward are identified. One invokes the induction of successful pathogenesis as a primary determinant in specificity while the other predicts that recognition of avirulent pathogens by the host leads to induced resistance which acts as the determinant in specificity. The former theory is supported by evidence for the appearance of novel host enzymes during disease development. The latter is supported by observations of host gene derepression and phytoalexin accumulation which occur in resistance responses at times prior to any significant response in susceptible combinations. These theories are examined experimentally in the flax/flax rust system. The molecular origin of ribonuclease with altered catalytic properties, which arises during disease development, is examined. Rigorous purification reveals that the altered catalytic properties can be accounted for by altered proportions of ribonuclease I isozymes. These changes are similar during resistant and susceptible reactions until sporulation occurs. Induced resistance is characterized and compared to primary changes during susceptibility through a detailed study of RNA and protein synthesis. Enhanced RNA synthesis occurs in the resistant reaction at times prior to any measurable response in the susceptible combination, although both combinations exhibit higher rates of RNA synthesis at later times. RNA was fractionated by electrophoresis and affinity chromatography and messenger activity assessed by in vitro translation. Enhanced RNA synthesis is characterized by decreased messenger polyadenylation. However, polyadenylated and non-polyadenylated messenger RNA were shown to encode many common polypeptides; this provides an explanation for the fact that few changes in iri vivo protein synthesis can be detected by one or two dimensional electrophoresis. The only marked changes in protein synthesis occur in the susceptible combination and include a dramatic decline in the synthesis of the large subunit of ribulose-1,5-bisphosphate carboxylase. It is concluded that incompatibility of an avirulent race of rust with the flax variety Bombay is determined by induced resistance resulting from recognition of the avirulent pathogen prior to the initiation of pathogenesis. However, specific biochemical events in the host, particularly those involving chloroplast function, may be necessary for successful pathogen development. / Land and Food Systems, Faculty of / Graduate

Developers face numerous challenges in their careers, including the critical decision of choosing the most suitable programming language to tackle these challenges. Each programming language presents its unique set of advantages and disadvantages, making the decision-making process complex. This study focuses on one such decision – the selection between Rust and C++ which are both systems programming languages with significant emphasis on performance. Rust, an emerging and increasingly popular language, offers a compelling alternative to the more established C++. To aid practitioners in making an informed decision, this study explores the performance differences between Rust and C++ through three distinct experiments: matrix multiplication, merge sort, and file I/O operations. The experiments reveal that C++ demonstrates significantly faster performance in matrix multiplication. Conversely, Rust showcases superior performance in merge sort, with both languages performing similarly overall. The findings pertaining to file operations were mixed, with C++ exhibiting shorter execution times for file reading, while Rust displayed an advantage in writing larger file sizes. By shedding light on these performance disparities, this study aims to assist developers in their decision-making process when selecting between Rust and C++.

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