Drought is a major limiting abiotic stress influencing wheat production in many parts of the world. The erratic nature of water deficits makes breeding and selection for drought resistance deficient. In environments with late season drought stress, yield losses are usually associated with kernel abortion or reduction in kernel growth. Remobilization of soluble carbohydrates from the stem has been associated with drought resistance. The objectives of this investigation were i) to asses the role of soluble carbohydrates in the determination of drought resistance, ii) their association with productivity, and iii) to evaluate a rapid technique to identify genotypes with higher capacity of soluble carbohydrate remobilization. Nine winter wheat cultivars differing in their response to drought stress were grown under irrigated and nonirrigated conditions during the grain filling period at the Sherman Branch Experiment Station, Moro. The cultivars were also grown at the Hyslop Crop Science Laboratory, where plots were chemically desiccated with Sodium Chlorate or left untreated. All control and treated plots were evaluated for soluble carbohydrates in two vegetative fractions, stem plus sheath and leaf blades. These values were correlated with the relative reductions in kernel weight and yield observed on the treated plots. Differences among cultivars were observed for the concentration of soluble carbohydrates in the stem and leaf fractions. Time elapsed from anthesis was a major determinant of the variation in carbohydrates concentration observed during grain filling. Stem soluble carbohydrates accumulated to a much greater extent than leaf soluble carbohydrates. The concentration of stem carbohydrates was not related with the reductions caused by chemical desiccation or drought stress. However, potential contributions from stem reserves (ratio between potential spike weight and stem reserves) were marginally associated with drought resistance. Stem soluble carbohydrates were positively associated with productivity, suggesting that stems are not competitive sinks, but temporary storage organs of excess of assimilates. Under chemical desiccation most of the soluble carbohydrates were lost in respiration, and the reductions in kernel weight and yield observed were not correlated with those observed under drought. It was concluded that the technique did not reasonably simulated drought in terms of yield reductions nor carbohydrate remobilization. / Graduation date: 1998

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1990. / Vita. Abstract. Includes bibliographical references (leaves 56-65). Also available via the Internet.

Strawbreaker foot-rot is a major limiting factor to cost efficient winter wheat production in the Pacific Northwest. Development of resistant cultivars has been hindered by the lack of adequate levels of genetic resistance and screening techniques which can consistently detect desired genotypes. Studies were conducted to determine if the reported strawbreaker foot-rot resistance of the cultivar "Rendezvous" is effective on isolates of Pseudocercosporella herpotrichoides found in the Pacific Northwest. Protected, naturally infected and artificially inoculated treatments were employed to determine the level of resistance of 10 cultivars including Rendezvous. Different concentrations of inoculum and stages of development were also used to determine if observations on leaf sheath penetration of seedlings obtained in the greenhouse were related to disease severity index readings taken in the field for selected cultivars. In addition, the nature of inheritance of strawbreaker foot-rot was studied in two crosses involving Rendezvous. Experiments were conducted at three locations and over two years at one location. Despite cultivar x treatment interaction, consistent levels of infection were observed in all experiments at each location. Significant differences were found for treatments and cultivars for most attributes. Yield losses, including the components of yield spikes per square meter, 1000 kernel weight, and kernel number per spike were proportional to the severity of the disease. Losses were greater when lodging occurred, which was also associated with disease severity. However, even in the absence of lodging losses were recorded in the naturally and artificially inoculated plots. Traits measured involving Rendezvous and Vpm/Mos 95//*2Hill were only slightly influenced by the treatments. Under greenhouse conditions, it was possible to distinguish the level of resistance of Rendezvous from susceptible cultivars at concentrations of 100 spores/ml, two weeks after inoculation at the seedling stage. Leaf sheath penetration of seedlings was found to be closely associated with the disease severity index obtained under field conditions. Generation means analysis performed in crosses involving Rendezvous indicated that additive and additive x additive gene action were responsible for most of the genetic variability associated with resistance. Narrow-sense heritability estimates also confirmed these fmdings. It would appear that Rendezvous has at least two major genes for resistance to strawbreaker foot-rot. / Graduation date: 1992

To remain competitive in the international marketplace, soft white wheat cultivars grown in the Pacific Northwest must have consistent and predictable flour properties including kernel texture. As a consequence, there is a need to develop wheat cultivars for specific end uses. Wheat cultivars with very soft kernels are used largely for making cookies and cakes. Harder soft white wheats are more suitable for noodles and flat breads. Numerous studies have been made to determine the inheritance of kernel texture between hard and soft wheat; however, very little information is available concerning the amount of genetic variability within soft white wheat. Reciprocal crosses were made between a very soft (TJB/MON"S") and a soft (Yamhill) white winter wheat genotype. Data were collected on an individual plant basis for kernel texture, protein content, and eight selected agronomic traits. Kernel hardness and protein content were determined using the near-infrared reflectance spectroscopy (NIR). Genetic differences for kernel texture and the other nine traits were found between the two parents and the resulting F1 progenies. It would appear that kernel texture is qualitatively inherited with one or more genes reflecting additive and nonadditive gene action. However, a large component of non-genetic variation was also detected. Of particular interest was the apparent reciprocal differences found between Fl populations for most of the traits measured and particularly kernel texture. However, for kernel texture, such differences were not due to a dosage effect of the 3n endosperm. Kernel texture was not found to be associated with protein content. A negative association of kernel texture with heading date would suggest a compromise may be necessary when selecting these traits. Positive associations were found between kernel hardness with number of tillers, total biological yield, grain yield, and number of kernels per spike. / Graduation date: 1992

The lack of information regarding the inheritance of the duration and rate of grain filling, and the possible relationship between grain fill and grain protein content in wheat prompted this study. Early maturing Chinese cultivars, 'AI Feng 2' and 'CB 83-52', and late maturing cultivars adapted to Oregon, 'Stephens' and 'Yamhill Dwarf', were examined for vernalization and photoperiod responses. Progeny from a diallel cross of the genotypes was evaluated for grain filling parameters, grain protein content and other agronomic traits for two years. 'Yamhill Dwarf' required six weeks of vernalization, while other cultivars needed only four weeks. The two Oregon developed genotypes were more sensitive to photoperiod than Chinese genotypes. Variation in developmental patterns among genotypes was related to differences in leaf number, spikelet number, rate of spikelet initiation, and rate of grain fill. Compared to solid planting, space-planting reduced the grain filling period. Significant genotypic variation for grain filling rate, duration, and kernel weight was observed in both seasons. Genotype X year interaction was not significant for any of the grain filling traits. General combining ability effects for grain filling rate, duration, and kernel weight were much larger than specific combining ability effects. Additive gene action made the major contribution to the inheritance of the grain filling traits. However, dominance effects appeared also to be involved in the genetic control of grain filling duration and kernel weight. Narrow sense heritability estimates were high for all three grain filling traits. Results indicated that early generation selection for both duration and rate of grain fill should be effective in these populations. Rate, but not duration of grain fill was closely associated with kernel weight. There was an inverse relationship between duration and rate of grain filling. Kernel protein percentage was positively associated with duration, but negatively related to rate of the grain filling. Results suggest that starch and protein accumulations in the kernel are two highly independent processes and may not necessarily compete for assimilates or energy. It may be necessary under the environments of this study to increase the duration of the grain fill to obtain high protein content with acceptable grain yield. / Graduation date: 1993

A negative relation between grain protein content and grain yield is frequently observed in wheat (Triticum aestivum L. em Thell) i.e. as grain yield increases, grain protein decreases. It has been suggested that the inverse relation between grain yield and protein is in part the result of developing high yielding semi-dwarf wheat cultivars with an increased harvest index. This investigation was undertaken to determine the nature of the possible association of grain yield and protein content as influenced by harvest index, biological yield, plant height and kernel weight in winter wheat populations grown in Oregon. Progenies derived from three crosses of winter wheat were solid-planted in two environments during two seasons. Phenotypic correlations showed a moderate negative association of grain protein content with both grain yield and harvest index. The magnitude of the genetic correlations suggested the presence of genetic relationships among these traits. Selection for harvest index among these crosses could cause a correlated reduction of grain protein content. To investigate if the relationships between grain protein content and selected plant growth traits were similar when grown under space-planted and solid seeded stands, progenies of two winter wheat crosses were evaluated during two seasons. Performance for grain yield and grain protein content was different under contrasting sowing densities as values were not correlated between sowing densities. This indicates the need to evaluate these traits in solid-seeded stands. Harvest index, as well as plant height and heading date, could be effectively selected under space-planted or solid seeded conditions. Associations among traits were reliably estimated in space-planted stands. To evaluate the effect on grain protein content when grain yield and harvest index are modified, the plant growth regulator Paclobutrazol was applied to selected winter wheat genotypes under field and greenhouse conditions. Paclobutrazol increased grain yield and harvest index values of all genotypes in the greenhouse, while only some genotypes improved these traits under field conditions. Grain protein content, however, remained unchanged. Higher grain yields were obtained in both greenhouse and field experiments. / Graduation date: 1991

Thesis (M.S.)--Oregon State University, 2010. / Printout. Includes bibliographical references (leaves 74-82). Also available on the World Wide Web.

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Master of Science / Agronomy / Guihua Bai / Guorong Zhang / Fusarium head blight (FHB) is one of the most damaging diseases in wheat, which impacts both grain yield and quality drastically. Recently, the disease has become more prevalent in the hard winter wheat (HWW) grown areas of the United States including Oklahoma where FHB has not been reported before. Growing resistant cultivars is the most economical and effective strategy for disease management. To dissect quantitative trait loci (QTL) for FHB resistance in a moderately resistant hard winter wheat (HWW) cultivar, Overland, a population of 186 recombinant inbred lines (RILs) was developed from the cross between Overland and Overley, a susceptible HWW cultivar from Kansas. The RILs were evaluated for FHB type II resistance in one field and three greenhouse experiments and genotyped using genotyping-by-sequencing (GBS) markers. Three FHB resistance QTLs were mapped on Chromosomes 4DL, 4AL, and 5BL. The QTL on 4DL was the most consistent one and explained up to 13% of the phenotypic variation for type II resistance and 14 % for low Fusarium damaged kernels (FDK). Two GBS markers closely linked to the 4DL QTL were successfully converted to Kbioscience competitive allelic specific PCR (KASP) assays and can be used in marker-assisted breeding. In breeding, a single QTL may provide only partial resistance and pyramiding of several resistance QTLs in a cultivar can provide more protection in FHB epidemics. Fhb1 is a major QTL for FHB resistance from a Chinese source and Fhb3 is an alien gene from wild rye grass (Leymus racemosus). To study the effects of these QTLs individually and cumulatively in hard winter wheat backgrounds, they were transferred into two HWW cultivars Overland and Jagger. The results show that Fhb1 significantly increased FHB resistance, but Fhb3 did not. Thus, Fhb3 is not an effective gene for improvement of FHB resistance in HWW.