Thesis (M.S. in plant pathology)--Washington State University, December 2008. / Title from PDF title page (viewed on Sept. 23, 2008). "Department of Plant Pathology." Includes bibliographical references.

Thesis (M.S.)--Washington State University, May 2006. / Includes bibliographical references.

Disease has been implied as an important selective force acting in plant populations. This study was conducted to determine the effects of stripe rust (Puccinia striiformis) on the population dynamics of wheat (Triticum aestivum) cultivar mixtures. Five wheat cultivars were grown in pure stands and all possible mixtures at three and two locations in 1987 and 1988, respectively. In 1989, four replacement series and their component pure stands were grown in two locations. All treatments were exposed to or protected from two stripe rust races. Disease severity and yield were determined on a per-cultivar basis for mixtures and also for pure stands. In all but one mixture, disease severity relative to the pure stands was reduced between 6 and 97%. Disease severity changes could be separated into two effects: First, selection for the more resistant or susceptible genotype reduced or increased disease in mixtures as compared to their pure stands by up to 47 and 11%, respectively. Second, epidemiological effects of host diversity reduced disease severity on individual cultivars below that of their pure stands. Disease severity on a genotype was often frequency-dependent. However, interactions among plant genotypes sometimes appeared to alter susceptibility and obscured the relationship. Non-diseased and diseased mixtures yielded 0 to 8% and 8 to 15% more than pure stands, respectively. overall, mixture yields were more influenced by plant-plant interactions than by disease. Population dynamics over time were studied by applying variable disease pressure to populations of four wheat cultivars for one-to-three generations in two locations. Fitnesses of genotypes were calculated by regressing the legit of a genotype's frequency on generation. Fitnesses were affected by disease and location and appeared constant over time. However, genotype frequency-changes were negatively correlated with planting frequencies, suggesting that fitnesses were frequency-dependent. Analysis of data from longer-term studies in the literature indicated that three generations may not have been sufficient to detect frequency-dependence. Stable equilibria may more likely exist for mixtures of genotypes that are closely related and adapted to the environment in which they are grown than for randomly selected genotypes. / Graduation date: 1992

Thesis (M.S.)--Oregon State University, 2010. / Printout. Includes bibliographical references (leaves 58-68). Also available on the World Wide Web.

Stripe rust of wheat, caused by Puccinia striiformis f. sp. tritici (Pst), is one of the most devastating diseases of wheat worldwide. Selection pressure on the pathogen population may result in a rapid shift to races virulent on wheat genotypes with specific resistance genes. For successful stripe rust management, it is important to monitor the virulence spectrum of the pathogen to detect new races. The purpose of this research was to survey Saskatchewan fields to determine the prevalence of stripe rust, characterize the race structure of Pst in western Canada and to determine the genotypic diversity of the pathogen population. Race characterization was performed by inoculating 27 near-isogenic wheat lines carrying 28 known resistance genes, four supplemental cultivars and one triticale cultivar with 61 genetically uniform Pst isolates from western Canada. Whole genome sequencing of pathogen isolates was conducted, using the Illumina HiSeq2500 platform and polymorphisms were assessed by single nucleotide polymorphism (SNP) variants. Characterization of Pst isolates identified 33 races of the pathogen. Genes Yr5, Yr15 and YrSP conditioned resistance against all isolates tested and all isolates were virulent on Yr6, Yr7, Yr9, Yr18, Yr28, Yr29 and Yr31. Variation for virulence was observed among isolates on Yr10, Yr24, YrTye, YrSu, Yr3 and Yr4. The analyses of virulence profiles divided the 61 isolates into four sub-populations or groups. These four sub-populations were distinct from each other in terms of virulence spectrum and year of collection. The Pst population in Alberta had greater diversity in terms of virulence compared with the Saskatchewan population. Diversity at the genome level was not observed to be related to geographic location or virulence phenotypes of the isolates. The SNP data revealed four sub-populations in the western Canadian Pst population. Genomic analyses of 48 Pst isolates did not reveal any relationship of the four sub-populations with their origin or year of collection. Signs of recombination were detected in the Pst population in western Canada. Genomic analyses differentiated isolates showing signs of recombination from those that did not.

Doctor of Philosophy / Department of Plant Pathology / Erick D. DeWolf / Stripe rust (caused by Puccinia striiformis f. sp. tritici) and leaf rust (caused by Puccinia triticina) are the top two diseases of winter wheat (Triticum aestivum) with a 20-year average yield loss of 4.9% in Kansas. Due to the significant yield losses caused by these diseases, the overall objective of this research was to identify environmental variables that favor stripe and leaf rust epidemics. The first objective was to verify the environmental conditions that favor P. triticina infections in an outdoor field environment. Wheat was inoculated with P. triticina and exposed to ambient weather conditions for 16 hours. Number of hours with temperature between 5 to 25°C and relative humidity >87% were highly correlated and predicted leaf rust infections with 89% accuracy. The results of this outdoor assay were used to develop variables to evaluate the association of environment with regional leaf rust epidemics. Before regional disease models can be developed for a forecast system, suitable predictors need to be identified. Objectives two and three of this research were to identify environmental variables associated with leaf rust and stripe rust epidemics and to evaluate these predictors in models. Mean yield loss on susceptible varieties was estimated for nine Kansas crop reporting districts (CRD’s). Monthly environmental variables were evaluated for association with stripe rust epidemics (>1% yield loss), leaf rust epidemics (>1% yield loss), severe stripe rust epidemics (>14% yield loss) and severe leaf rust epidemics (>7% yield loss) at the CRD scale. Stripe rust and leaf rust epidemics were both strongly associated with soil moisture conditions; however, the timing differed between these diseases. Stripe rust epidemics were associated with soil moisture in fall and winter, and leaf rust epidemics during winter and spring. Severe stripe rust and leaf rust epidemics were associated with favorable temperature (7 to 12°C) and temperature (15 to 20°C) with relative humidity (>87%) or precipitation in May using tree-based methods of classification, respectively. The preliminary models developed in this research could be coupled with disease observations and varietal resistance information to advise growers about the need for foliar fungicides against these rusts in Kansas winter wheat.

Graduation date: 2002

Stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is an economically important foliar disease of wheat (Triticum aestivum). In the last decade, losses from stripe rust in North Dakota (ND) have increased, peaking at 5% in 2015. Three research studies were conducted to address questions on the pathogen, varietal resistance, and integrated management. The objective of the first study was to (i) identify virulent phenotypes of Pst isolates collected from ND from 2015 to 2017 and assign races, and (ii) determine the effect of temperature on in vitro urediniospore germination, latency, and lesion spread. Across the three years, five races were detected with PSTv 37 being the most common. The highest urediniospore germination occurred at 12oC followed by 16oC. Pst isolates had shorter latency at 21oC and larger lesion spread at 16oC. The objective of the second study was to evaluate seedling resistance and adult plant resistance in the North Dakota State University spring wheat breeding program using races PSTv 37 and PSTv 52. Results from seedling experiments indicated only four and two lines were resistant to PSTv 52 and PSTv 37, respectively. Adult plant resistance experiments were unsuccessful in 2019, and will be conducted again in the future. The objective of the third study was to develop fungicide timing recommendations for wheat rust (stripe and leaf) based on varietal resistance and time of disease onset. Rust developed in five of the eight field trials, and timing of disease onset was categorized by growth stage (tillering, flag leaf, or early-flowering). Results indicated fungicide application timing was influenced by timing of disease onset and varietal resistance. When rust was detected at the tillering growth stage on the susceptible variety, the best time to apply a fungicide was at Feekes 9. When rust was detected at flag leaf or beyond on a susceptible variety, a fungicide application at Feekes 10.51 provided the adequate disease reduction and protection of yield. Results from these research studies provide a better understanding of Pst, determined seedling resistance in the breeding program, and provides field data to refine management recommendations for wheat rusts in ND. / North Dakota Wheat Commission / State Board of Agricultural Research and Education

Challenges to growing winter wheat in North Dakota include winter temperature and disease pressure. Fusarium head blight (FHB) is a devastating disease that necessitates breeding for resistance. In the NDSU breeding program FHB resistance genes are often associated with a decrease in performance. This study used single seed descent to advance lines while maintaining a near random population. Early generation (F4) selection focused heavily on yield and the presence of FHB resistance quantitative trait loci to develop winter wheat lines with FHB resistance and high yield. Stripe rust is a fungal disease that is becoming increasingly problematic in North Dakota. To assess the available stripe rust resistance in the NDSU winter wheat germplasm, two sets of diverse breeding lines were used for stripe rust resistance phenotyping and genotyping by sequencing. The phenotype and genotype data were then used to locate resistance genes through genome wide association study.

Fall-sown barley will be increasingly important in the era of climate change due to higher yield potential and efficient use of water resources. Resistance/tolerance to biotic and abiotic stresses will be critical. Low temperature is an abiotic stress of great importance. Resistance to barley stripe rust (incited by Puccinia striifomis f. sp. hordei) and scald (incited by Rhynchosporium secalis) will be important in higher rainfall areas. Simultaneous gene discovery and breeding will accelerate the development of agronomically relevant germplasm. The role of FR-H1 and FR-H2 in low temperature tolerance (LTT) has been well documented. However the question still remains: is LTT due only to FR-H1 and FR-H2 or are there other, undiscovered, determinants of this critical trait? We developed two doubled haploid mapping populations using two lines from the University of Nebraska (NE) with superior cold tolerance and one line from Oregon State University (OR) with good malting quality and disease resistance: NB3437f/OR71 (facultative x facultative) and NB713/OR71 (winter x facultative). Both were genotyped with a custom 384 oligonucleotide pool assay (OPA). QTL analyses were performed for LTT, vernalization sensitivity (VS), and resistance to barley stripe rust and scald. Disease resistance QTL were identified with favorable alleles from both NE and OR germplasm. The role of VRN-H2 in VS was confirmed and a novel alternative winter allele at VRN-H3 was discovered in the Nebraska germplasm. FR-H2 was identified as a determinant of LTT and a new QTL, FR-H3, was discovered on chromosome 1H that accounted for up to 48% of the phenotypic variation in field survival at St. Paul, Minnesota, USA. The discovery of FR-H3 is a significant advancement in barley LTT genetics and will assist in developing the next generation of fall-sown varieties. / Graduation date: 2012