Browsing by Subject "Near isogenic lines"

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    Towards positional cloning and functional analysis of genes that control wax production in barley
    (2018-09) Tandukar, Zenith
    Epicuticular waxes are the first point of contact between plants and their external environment, and provide mechanical and physiological support to plants. The leaf sheath and spike waxes of barley are rich in beta-diketone and hydroxy-beta-diketones that gives barley waxes a pronounced thread-like and fibrous morphology. Two previously described mutants are the subjects of this study namely: glossy sheath 2 (gsh2) and Glossy spike (Cer-yy). Both mutants exhibit a glossy (lack of epicuticular waxes) phenotype on the spike, while the gsh2 mutant also exhibits a glossy phenotype on the leaf sheaths on upper leaves. In this study, the gsh2 and Cer-yy mutants were exploited (1) to gain an increased understanding of the developmental timing and tissue specificity of wax accumulation; (2) to determine if gsh2 and/or Cer-yy mutants impact water retention; and (3) to fine map and identify candidate genes for GSH2 and CER-YY. Compared to wildtype, both mutants exhibited an absence of thread-like and fibrous waxes in the upper leaf sheaths and spikes, but an increased presence of plate-like lobed waxes following the elongation of the third internode. No significant differences in whole plant transpiration rates were observed between Bowman-gsh2, Bowman-Cer-yy and cv. Bowman in either high and low vapor pressure deficit conditions. Fine mapping populations segregating for GSH2 and CER-YY reduced the regions containing GSH2 to ~600Kbp and CER-YY to ~1.2 Mbp. Each region contains multiple candidate genes based on their functional annotation that warrant further research to isolate the respective causative genes.
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    Using near isogenic barley lines to validate Deoxynivalenol (DON) QTL previously identified through association analysis
    (2013-01) Navara, Stephanie Lynn
    Fusarium head blight (FHB) is a serious disease of cereal grains caused by the fungal pathogen Fusarium graminearum. Deoxynivalenol (or DON), the associated trichothecene mycotoxin is of special concern to barley producers and consumers. A recent association mapping (AM) study of U.S. six-row spring barley identified several modest effect quantitative trait loci (QTL) for DON and FHB. To date, few studies have attempted to verify the results of association analyses, particularly for complex traits such as FHB and DON resistance in barley. Despite control measures used to mitigate the effects of population structure and multiple testing in AM, false positives may still occur. To verify previously reported associations we evaluated the effects of nine DON QTL using near isogenic lines (NILs) for each QTL region. Families of contrasting homozygous haplotypes for each region were derived from lines in the original AM populations that were heterozygous for DON QTL. Seventeen NIL families were evaluated for FHB and DON in three field experiments. Significant differences between contrasting NIL haplotypes were detected for three QTL across environments and/or genetic backgrounds, thereby confirming QTL from the original AM study. Several explanations for those QTL that were not confirmed are discussed, including the effect of genetic background and incomplete sampling of relevant haplotypes.