Graduate Thesis Or Dissertation
 

Effect of moisture stress on yield and quality of winter wheat seed

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  • Two experiments were conducted to determine the effects of moisture stress on physiological changes that occur during the vegetative and reproductive stages of the wheat (Triticum aestivum L.) plant, and to relate these effects to seed yield, quality and performance. In a field experiment, different levels of moisture stress were obtained by establishing plots in two rainfall areas, and by planting on three different dates in the dryland area. Seed development and maturation occurred under extreme moisture stress in Moro (254mm annual rainfall), while stress at Corvallis (1020 mm annual rainfall) was low. Plants from the early fall planting were subjected to the most stress because of the greater fall growth which removed much of the soil moisture. Lowest seed yields occurred under the greatest moisture stress conditions, primarily because of a reduced number of seeds per spike. Seed size was the quality component most affected by moisture stress. Smaller seed size was associated with lower soil water potential, higher leaf area index during vegetative growth, and higher specific leaf weight and water soluble carbohydrate content of the plants after anthesis. Water soluble carbohydrate content was particularly high in the rachises of the most severely stressed plants, indicating a reduced rate of translocation to the developing seeds. Embryo weight was also reduced in the more stressed plants in proportioa to the reduction in seed weight. The protein contents of seeds from all three moisture stress levels at Moro were similar. Seeds developed under the most severe water stress had the highest respiratory quotient and lowest glutamic acid decarboxylase activity. The growth rate of seedlings produced by these seeds was 29% lower than that from seeds from the less stressed plots. A greenhouse experiment was conducted to study the effects of water stress under controlled conditions. Plants were grown under three moisture regimes (600, 300 and 150 ml water/pot/day) from the time awns were first visible on the main stem until maturity. Water-stressed plants had smaller leaf area and leaf dry weight, higher specific leaf weight, earlier leaf senescence, lower dry weight, and lower seed yield. On the other hand, water-stressed plants produced larger seeds, with heavier embryos, higher protein content, lower CO₂ evolution and lower respiratory quotient. These seeds in turn produced seedlings with greater vigor in terms of seedling growth rate. Because of the compensation ability of the wheat plant, development of management practices to decrease certain yield components in favor of enhanced seed quality is worthy of further study.
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