Browsing by Subject "Quantitative trait loci"

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    The Adaptive Value and Genetic Basis of Maternal Effects in Competitive Environments
    (2008-10) Dechaine Berkas, Jennifer M.
    Plants rely heavily on environmental cues to direct life-history processes. In many species, the maternal environment is a reliable predictor of environmental conditions in the next generation, and several aspects of progeny phenotype are responsive to environmental cues during seed maturation. The ratio of red to far-red light (R:FR) is one environmental cue that has been widely shown to influence plant phenotypes across generations. Low R:FR are predictive of competitive conditions, because chlorophyll in neighboring leaves absorbs red light but allows far-red light to pass through. It has been suggested that effects of the maternal competitive environment on progeny phenotype are adaptive, but very few studies have convincingly tested this hypothesis. In addition, the genetic basis of environmental maternal effects is poorly understood. In this dissertation, I examine the adaptive value and genetic basis of maternal effects in competitive environments in the plant species Brassica rapa and Arabidopsis thaliana. In chapter 1, I investigate the adaptive value of maternal effects across two generations of competitive environments in B. rapa. Maternal environment effects did not enhance progeny fitness but did influence several other progeny traits, as well as selection gradients in the progeny generation. These results suggest that although environmental maternal effects are not adaptive in this study, they are genetically variable and may evolve or affect the evolution of progeny traits. I further investigate the effects of competition on B. rapa fitness traits in chapter 2, in which I use a quantitative trait loci (QTL) mapping approach to examine how the genetic architecture of multiple components of fitness differs across competitive environments. QTL expression varied across competitive treatments for total fruit production, but QTL were generally conserved in other fitness traits. In addition, I identify environment-specific QTL for seed mass and germination timing in seeds matured under a low R:FR. Lastly, in chapter 3, I investigate if and how phytochrome photoreceptor genes mediate the effects of maternal R:FR on progeny germination. My results suggest that all 5 phytochrome genes in A. thaliana partially mediate progeny germination response to maternal R:FR, and I identify novel roles for individual phytochrome loci in this response. As a whole, this research provides insight into the extent that maternal effects in competitive environments are adaptive and partially elucidates the genetic basis of maternal effects.
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    Sources of FHB Resistance, Genetics and Mapping of Stem Rust Resistance in Kenyan and Ethiopian Spring Wheat Germplasm
    (2019-11) KOSGEY, ZENNAH
    Fusarium head blight (FHB or scab) and stem rust are important diseases of wheat. Fusarium graminearum is considered the primary causal agent of FHB. This study evaluated 215 wheat genotypes from Kenya and Ethiopia for their response to F. graminearum in inoculated and mist-irrigated nurseries established in St. Paul, MN in 2016, St. Paul, MN in 2017 and Crookston, MN in 2017. Six genotypes with stable resistance across the three test locations were identified. Positive associations were identified between FHB index, VSK, and DON and negative associations were identified between FHB index, plant height, and heading dates. The response of select genotypes was confirmed under greenhouse conditions. These studies identified resistance sources that can be used to improve the resistance levels in Kenyan and Ethiopian wheat germplasm. Stem rust caused by Puccinia graminis f. sp. tritici remains a threat to wheat production in East African wheat growing regions. In this study, we characterized the genetics of stem rust resistance, identified QTLs and markers associated with the resistance in spring wheat line CI 14275. The RILs together with their parents were evaluated at the seedling stage in a biosafety level 3 greenhouse against Pgt races TTKSK and TRTTF and in the USDA-ARS Cereal Disease Lab greenhouse against Pgt races TPMKC, TTTTF, and RTQQC. Screening for resistance to Pgt races in the field was undertaken in Kenya, Ethiopia, and the US in 2016, 2017, and 2018. One and three complementary genes conferred resistance to races TTTTF and RTQQC, respectively. The QTL QSr.cdl-2BS.2, that conferred resistance in Kenya and Ethiopia was validated and the marker Excalibur_c7963_1722 was shown to have potential in marker assisted selection. This is the first study to both detect and validate an adult plant stem rust resistance QTL on chromosome arm 2BS. The QSr.cdl-3B.1 is likely Sr12, QSr.cdl-4AL.1 is postulated as Sr7a, QSr.cdl-6BL.1 is likely Sr11, and QSr.cdl-6AS.1 appears to be a new QTL. Combination of QSr.cdl-2BS.2, QSr.cdl-3B.1, and QSr.cdl-6AS.1 has the potential to reduce stem rust severity in Africa. The work presented on FHB and stem rust provides resources for wheat improvement in East Africa.