Graduate Thesis Or Dissertation
 

Temperature and moisture effects on stand establishment of seven winter wheat cultivars and selected progeny (Triticum Aestivum, L em thell

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  • Laboratory studies were conducted under different temperature and moisture regimes to evaluate the effects of temperature and moisture on stand establishment and seedling characteristics associated with stand establishment. Percent stand and days to 25% emergence were used as indexes of stand establishment. Seedling characteristics analyzed were: shoot length, coleoptile length, seedling dry weight, and Adenosine Triphosphate (ATP) content. Each of these characteristics were tested with regards to predicting stand establishment over a wide range of temperature and moisture conditions. Experiments on stand establishment were also conducted under field conditions at the Sherman Experiment Station in north-central Oregon. The degree of association between stand establishment estimates obtained in the field and estimates of stand establishments obtained in the laboratory was determined. Attempts were also made to determine the mode of inheritance of coleoptile length and Adenosine Triphosphate and the association of these characteristics with stand establishment in early generations. Seven soft white winter wheat cultivars (Yamhill, Moro, Stephens, McDermid, Hyslop, Luke, and Daws) were used in the laboratory and field experiments. Parents, F₁ s, and F₂s from crosses among four of the cultivars (Yamhill, Moro, McDermid, and Daws) were utilized in the inheritance studies of coleoptile length and ATP. Broad sense heritability estimates for coleoptile length were computed using the parental and F₂ variances. Frequency distribution of coleoptile length were tested for their fit to normality by use of the chi square test. Narrow sense heritability estimates for coleoptile length and Adenosine Triphosphate were computed using the standard unit (correlation) and regression methods. Three temperatures levels 8, 15, and 22°C) and three soil moisture levels (-2, -4, and -6 bars) were used to study the effects of temperature and moisture on stand establishment and stand establishment characteristics of the seven cultivars in the laboratory. Different temperature and moisture levels exhibited significant effects on percent stand, days to 25% emergence, shoot length, coleoptile length, seedling dry weight, and ATP. Increasing temperature from 8 to 22°C resulted in decreases in percent stand, days to 25% emergence, and coleoptile length. Shoot length, seedling dry weight, and ATP increased as temperature was increased from 8 to 22°C. Increasing moisture stress from -2 to -6 bars had a significant negative effect on percent stand, emergence rate, and each of the seedling characteristics studied. Coleoptile length was found to be the best predictor of percent stand over the entire range of temperature and moisture combinations utilized in the laboratory. Percent stand was observed to decrease whenever coleoptile length was less than the depth of planting. Shoot length was found to be the best predictor of days to 25% emergence over the entire range of temperature and moisture levels. Semi-dwarf cultivars produced poorer stands than tall cultivars due to their coleoptile length. This difference in stand establishment capability was most pronounced under the warmest temperature (22°C) and the greatest moisture stress (-6 bars). Estimates of minimum gene number together with data obtained from frequency distribution indicated that the inheritance of coleoptile length was controlled by one to three major genes and possibly some modifier genes. The close agreement between broad and narrow sense heritability estimates indicated that the expression of coleoptile length is controlled primarily by additive gene action. This suggests that selection for coleoptile length in early generations should give reliable estimates of coleoptile length expression in later generations. The heritability of Adenosine Triphosphate (ATP) was found to be subject to cytoplasmic influence. Maternal effects in the F₁ generation, the occurrence of considerable inbreeding depression in the F₂ generation, and relatively low narrow sense heritability estimates suggest that ATP can not be used as a selection character for seedling vigor in early generations of wheat in a conventional breeding program. Several characteristics (coleoptile length, ATP, plant height, and seed weight) were tested for their association with percent stand in the F ₁ and F₂ populations. None of these characteristics were significantly correlated with percent stand. Of these characteristics, coleoptile length produced the highest correlations with percent stand in the F ₁ and F₂ generations. The use of coleoptile length as a selection character for percent stand in early generations appears promising.
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