Browsing by Subject "Rust"

Now showing 1 - 4 of 4
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    Development Of Barley Introgression Lines Carrying The Leaf Rust Resistance Genes Rph1 To Rph15
    (2018-07) Martin, Matthew
    Barley (Hordeum vulgare) is the fourth most planted and harvested grain crop in the world. In many production areas, barley is attacked by the leaf rust pathogen (Puccinia hordei), a basidiomycetous fungus that reduces both its yield and quality. Many leaf rust resistance genes, known as reaction to P. hordei (Rph) genes, have been described in barley. Resistance deployed in cultivars has often been transient due to the pertinacious nature of single gene virulence mutations in P. hodei populations. To differentiate genetic variants for virulence in P. hordei populations, plant pathologists use barley accessions with different resistance genes, referred to as a differential set. The barley leaf rust differential set evolved through time as more Rph genes were described. The sources of Rph1-15 were derived from barleys with diverse geographic origins and agro-morphological traits. Ideal differential sets include lines where single resistance genes are backcrossed into the genetic background of an adapted susceptible cultivar. Sources for Rph1-15, along with many other Rph gene donors were backcrossed to the susceptible cultivar Bowman. Overall, 95 Bowman introgression lines for leaf rust resistance were developed, and a single line was recommended for use as the new backcrossed differential host line for each individual Rph1-15 gene. Genomic positions and gene candidates for Rph1-15 were characterized and the existence of possible new resistance genes was postulated. The new Bowman Rph1-15 differential lines will facilitate the efficient virulence phenotyping of P. hordei and serve as valuable genetic stocks for Rph gene stacking and cloning in barley.
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    Genetic and Genomic Analysis of Nonhost Resistance to Wheat Stem Rust in Brachypodium distachyon
    (2016-08) Della Coletta, Rafael
    Wheat stem rust, caused by the fungus Puccinia graminis f.sp. tritici (Pgt), is a devastating disease that has been under control for decades. However, new races of this pathogen have emerged that overcome many important wheat stem rust resistance genes, and their spread toward important areas of wheat production threatens global wheat production. Nonhost resistance in plants, which provides durable and broad-spectrum resistance to non-adapted pathogens, may hold great potential to help in the control of wheat stem rust, but the genetic and molecular basis of nonhost resistance is poorly understood. This research project employed the model plant Brachypodium distachyon (Brachypodium), a nonhost of Pgt, for genetic analysis to map loci associated with nonhost wheat stem rust resistance. Using bulked segregant analysis, next-generation sequencing, and bioinformatics approaches, seven quantitative trait loci were found to contribute to nonhost stem rust resistance in a recombinant inbred population derived from a cross between two Brachypodium genotypes with differing levels of resistance. In a second study, analysis of a Brachypodium recombinant inbred population segregating for an induced mutation that confers susceptibility to wheat stem rust led to the identification of a one base pair deletion in a gene that may be the cause of the mutant’s susceptibility. The gene is a homolog of the Arabidopsis gene TIME FOR COFFEE (TIC), which plays a role both in circadian clock regulation and jasmonate signaling. Collectively, the findings of this research project advance our understanding of the genetic basis of nonhost resistance to wheat stem rust, and will guide future research aiming to identify genes essential to the nonhost resistance response, as well as their mechanisms of action.
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    Genetics of Rust Resistance in a Wheat Nested Association Mapping Population
    (2017-10) Manan, Fazal
    Wheat is an important food crop in many parts of the world, but its genetic diversity has been eroded due to intense selection in breeding programs. To increase genetic diversity in the Minnesota wheat breeding program, a nested association mapping population was developed by crossing 25 exotic accessions selected from the USDA-ARS Spring Wheat Core Collection with RB07, a Minnesota cultivar selected as the common parent because it has wide adaptation in the region. Virulent races of the stem rust (Puccinia graminis f. sp. tritici, Pgt), leaf rust (P. triticina, Pt), and stripe rust (P. striiformis f. sp. tritici, Pst) pathogens threaten the wheat crop in the region. Thus, the objective of this thesis was to elucidate the genetics of rust resistance in select families of the Minnesota Nested Association Mapping Population (MNAMP) based on qualitative (chi-square tests of Mendelian gene models) and quantitative (quantitative trait loci (QTL) mapping with 66,685 single nucleotide polymorphic markers) genetic analyses. Four families segregated for resistance to the widely virulent Pgt races of TTKSK, TRTTF, and TTKST. One to five Mendelian genes and five to 19 QTL conferred stem rust resistance in individual families. One family segregated for resistance to Pt race TFBGQ with Lr21 virulence. One Mendelian gene and two QTL controlled resistance to this pathogen race. Three families segregated for resistance to the Pst races PSTv-37 and PSTv-40. Three to five Mendelian genes and two to 12 QTL conferred resistance to these races in individual families. Rust resistant progeny identified from the MNAMP will be useful for enhancing the resistance of wheat to the three rust diseases.
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    Genetics, Sources, and Mapping of Stem Rust Resistance in Barley
    (2017-04) Case, Austin
    Stem rust is a devastating disease of cereal crops worldwide. In barley (Hordeum vulgare), the disease is caused by two pathogens: Puccinia graminis f. sp. secalis (Pgs) and Puccinia graminis f. sp. tritici (Pgt). In North America, the stem rust resistance gene Rpg1 has protected barley from losses for more 60 years; however, widely virulent Pgt races from Africa in the Ug99 group threaten the crop. To identify novel quantitative trait loci (QTL) for stem rust resistance, bi-parental and association mapping studies were undertaken in the Barley iCore Collection (BCC) held by the USDA National Small Grains Collection. Association mapping studies of the BCC were conducted for seedling resistance to Pgt race TTKSK (Ug99 group) in the greenhouse and adult plant resistance (APR) to Pgt TTKSK composite in Njoro, Kenya and Pgt race QCCJB in St. Paul, MN. A major effect QTL (Rpg-qtl-5H-11_11355) for APR in all locations was identified on chromosome 5H. This QTL represents a unique locus for APR and has been confirmed in other studies. Subsequently, 290 of the most resistant BCC accessions, the BCC Selects (BCCS), were screened for resistance Pgt races MCCFC, QCCJB, HKHJC, TTKSK, TTKST, TKTTF, and TRTTF, and also Pgs isolate 92-MN-90. From this investigation, four BCCS accessions were postulated to carry Rpg1, 14 to carry Rpg2, 91 to carry Rpg3, four to carry rpg4/Rpg5, and 59 to carry potentially novel resistance genes. To map the APR genes of Rpg2 and Rpg3 in Hietpas-5 (CIho 7124) and GAW-79 (PI 382313), respectively, two biparental populations were developed with Hiproly (PI 60693), a stem rust susceptible accession. Both populations were phenotyped to the domestic Pgt races of MCCFC, QCCJB, and HKHJC in St. Paul and to Pgt TTKSK composite in Njoro. In the Heitpas-5/Hiproly population, a major effect QTL was identified on chromosome 2H, which is proposed as the location for Rpg2. In the GAW-79/Hiproly population, a major effect QTL was identified on chromosome 5H and is the proposed location for Rpg3. The resistance sources identified and characterized in this study enhance barley breeding programs focused on stem rust resistance.