Graduate Thesis Or Dissertation
 

Adaptability of winter wheat cultivars to dryland conditions and their response to water stress

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  • Winter wheat cultivars (Triticum aestivum) were evaluated for their response to water stress and adaptability to a wide range of moisture limited environments. Grain yield was analyzed for ten cultivars at six locations across four years. Regression of the cultivar mean on the year-location mean was used as a measure of the environmental response of a particular cultivar, Plant water status (leaf osmotic potential and water potential) during the grain filling period, along with grain yield and yield components were determined at three locations for fifteen cultivars under space-planted conditions in 1972 and for ten cultivars under solid-seeding in 1973. Five cultivars were evaluated for plant water status and rates of growth during reproductive development and for final grain yield and yield components at a severely stressed location in 1973. Drought resistance, described as yielding ability under severe soil moisture stress, was found to be the result of avoidance, tolerance and escape characteristics. Plant water status influenced the components of yield when their development occurred during a period of high external stress. However, the relative importance of plant water status to final yield varied depending on the magnitude of the direct effect of spike number on yield. Drought avoidance was the ability to maintain a high plant water status when under high external stress conditions. In the cultivar Yamhill, the stable growth rate during inflorescence development and the extended period of grain filling may have resulted from the ability of this cultivar to avoid drought. These characteristics, also, may explain the large spikelet number and the high kernel weight of Yamhill. Even though Hyslop and Wanser had a moderate and high internal water stress, respectively, they were relatively tolerant of stress in terms of high growth rates during the grain filling period. The high yielding ability of Wanser and McDermid under high stress conditions was primarily related to a large number of spikes. This trait was considered an escape characteristic because tillering was established before the onset of severe stress. The club wheats neither avoided or tolerated internal water stress under solid-seeded conditions nor did they have sufficient tillering capacity to compensate for the effect of stress on the laterdeveloped components.of yield. Nugaines, Hyslop and Rew maintained a moderate internal stress during later development but differed in their yield component responses. The yield of Nugaines depended primarily on a high tillering capacity, whereas the yield of Hyslop and Rew depended on a balance of contributions from all the components of yield. Widely adapted cultivars, such as Hyslop and McDermid, not only yielded well under severe stress conditions but had the genetic potential to respond adequately to more favorable moisture conditions. Cultivars specifically, adapted to lower yielding environments, such as Yamhill and Wanser, were able to avoid, tolerate or escape drought but were limited in one or more of their yield component responses to better conditions. Conversely, cultivars specifically adapted to high yielding environments, such as Nugaines and Paha, lacked the ability to consistently yield well under high stress environments but had a high response to more favorable moisture conditions. Cultivars best adapted to dryland cultivation should have the highest yield under stress conditions as expressed through the components of yield by one or a combination of avoidance, tolerance or escape characteristics. These cultivars should also have the maximum expression in, and balance among, the components of yield for maximum response to more favorable moisture conditions. This goal may be obtained by selection in favorable as well as stressed environments and by testing throughout the range of the environments where the cultivar is expected to be grown. Because high yield under stress was found in this study to be manifested through different characteristics of the plant the breeder should be aware of traits which may contribute to drought resistance, but he should not be restricted to a particular ideotype when breeding for yield under conditions of high moisture stress.
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