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

This study attempts to determine whether or not Portuguese wheat policies have resulted in a stabilization of the wheat price and/or the stabilization of income for wheat growers in the Alentejo region. It was found that these policies have contributed to a stabilization of price rather than a stabilization of income. It was also found that the income variability caused by yield variability was greater for the Alentejo farmers than that for the country as a whole. Weather uncertainties measured by rainfall were found to be a major source of that variability in both area and yield equations. Therefore, it was concluded that rainfall is significant in explaining variations in wheat supply and cannot be eliminated from the model specification. Finally, this study looked at a policy that would stabilize output returns to Alentejo farmers since high yield variability will continue to constrain farmers' willingness to invest in wheat production. An insurance program may be the policy to implement in this region since yield risks are the predominant source of income variability. However, the cost of financing an agricultural insurance scheme as well as the delineation of homogeneous areas are crucial determinants to the success of an all-risk insurance program.

Thesis (MScAgric (Agronomy))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: See full text for the abstract / AFRIKAANSE OPSOMMING: Sien volteks vir opsomming

Despite many investigations genotype by environment interaction remains one of the least understood factors in plant improvement. Understanding genotypic differences responsible for such interactions could assist in making more informed breeding decisions. The components of yield being less complex than grain yield per se may be useful for selection to improve adaptation of genotypes and enhance grain quality. However, the potential compensatory response among the components of yield could compromise their usefulness as selection criteria. To evaluate this aspect fifteen cultivars, including Soft White, Hard White and Hard Red wheats, were planted at three diverse locations over two growing seasons. Genotypes were ranked based on measurements for specific traits in each environment. The genotype by environment interaction for grain yield, protein concentration and hardness were investigated according to the AMMI model. Influence of environmental factors and genotype by environment interactions on associations among selected traits were determined. The results of this study showed that genotypic differences in adaptation to the Pacific Northwest and resistance to Septoria spp. were responsible for interactions for grain yield. However, no consistent patterns of response were found among the similar cultivars for quality traits. Those environments that favored expression of biomass and grain weight potential provided for enhanced performance of the adapted cultivars. The environments with suppressed biomass accumulation and grain filling interacted positively with the unadapted cultivars. A large compensatory relationship between tillering and apical growth was detected. No or low compensation was observed between grains per spike and thousand kernel weight. Two different strategies were proposed for improvement of Soft and Hard White wheat cultivars under the conditions of the Pacific Northwest. Both strategies accentuate importance of increasing biomass while maintaining harvest index. When selecting for higher yielding Soft White cultivars, plants with larger leaves, stronger stems, larger spikes and heavier grains should be emphasized. For Hard Whites - higher number of tillers and grains m����� is desired, as they provide for harder grains with higher protein content. / Graduation date: 2000

This thesis presents an investigation of two production functions (a non-linear-in-parameters and a generalized polynomial) in order to determine which function most appropriately represents the observed relationships of the components of ICM technology. Four spring barley and one spring wheat datasets were assembled from ICM field trials conducted in the Montreal region (1987-89). / A quadratic and a Mitscherlich-Baule equation were fitted to the (five) datasets and compared with respect to a number of measures of goodness of fit. One dataset was chosen for generating and graphing a three-dimensional response surface, based on the fitted equations of that dataset. The two surfaces were compared in light of expectations regarding the two equations. / The fitted equations of three of the five datasets did not produce noteworthy results. The other two datasets provided mixed results. The response surfaces provided outcomes that were contrary to prior expectations. In general graphing the response surfaces offered limited additional insight. Ultimately, this project may have been hampered by the experimental design of the field trials, those designs being oriented to results of agronomic rather than economic significance.

No description available.

M.S.

Under the conditions of the Rotation Experiment with Fertilizers, the following results were obtained with corn: The phosphorous plat, complete fertilizer plat and the manure plats produced a much higher yield of corn than the check plat. Also, these plats produced a higher percentage of marketable grain than the other plats. There was not much difference in the shelling percentage from the various plats but it was somewhat lower on the nitrogen and the floats plats. The nitrogen-phosphorous plat produced the greatest number pounds of shelled corn per pound of stover. The complete fertilizer plat also produced a high percentage of grain to stover. The percentage of matured ears was greatly increased on the nitrogen-phosphorous plat and the three manure plats. The corn plants on the manure plat developed sooner than those on the other plats while those of the check plat developed later. Also, the plants were larger in circumference and in height on the manured plat. The means of the corn characters were greater on the fertilized plats than on the check plat, and the means increased as the productivity increased. On the whole, the constants of variation were greater on the fertilized plats than on the check plat. The differences were sufficiently great to indicate that they were significant. On the whole, the coefficients of correlation of the corn characters were greater on the fertilized plats than on the check plat but the odds do not show that they are significant. Opposite results were obtained with wheat which is shown in Table 9. Also, in the case of wheat, the odds on the whole are not significant . In summing up all of the data in this experiment, it may be said that manure and acid phosphate were the chief limiting factors affecting yield. High yield of corn is usually accompanied by a high percentage of marketable grain, high shelling percentage, high ratio of grain to stover, high percentage of matured ears, and early maturity of plants. / Master of Science

M.S.

Graduation date: 1992