Browsing by Subject "Stem rust"

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    Genetic characterization of multiple disease resistance and agronomical/nutritional traits in hordeum
    (2013-08) Mamo, Bullo Erena
    Barley is an economically important crop plant whose yield and quality is affected by multiple diseases. Landrace and wild barley gene pools can be utilized to enhance disease resistance and nutrition in cultivated barley. To identify and map resistance loci for three important diseases (stem rust, spot blotch and Fusarium head blight [FHB]), and enhanced accumulation of two vital micronutrients (zinc and iron), genetic mapping was employed. The genetics of resistance to stem rust race TTKSK in Swiss landrace and wild barley accessions at the seedling stage was conducted through bi-parental mapping. Genetic analysis of F2:3 families derived from these accessions revealed that a single gene that maps to chromosome 5HL — at or in close proximity to the complex stem rust resistance locus rpg4/Rpg5 confers resistance. An association mapping approach was utilized to identify Quantitative Trait Loci (QTL) associated with disease resistance and zinc and iron concentration in 298 Ethiopian and Eritrean barley landraces genotyped with 7,842 single nucleotide polymorphism (SNP) markers. For stem rust race TTKSK, five seedling resistance loci were identified: one each on chromosome 2HS, 2HL, 3HL, 4HL, and 5HS. The ones on chromosomes 2HL and 4HL are novel, whereas the other three mapped to regions coincident with previously reported stem rust resistance QTL. For stem rust race MCCFC at the adult plant stage, one locus coincident with a known race TTKSK resistance QTL was identified on chromosome 5HL. For spot blotch, SNP markers located in close proximity with known adult plant spot blotch resistance QTL were found on chromosomes 2HL and 4HS in six-rowed barley landraces. For FHB, one common resistance QTL on chromosome 2HL, also associated with deoxynivalenol (DON) concentration, was identified. A locus mapping to a region of chromosome 4HL, known to contain QTL associated with DON, also was detected. The loci identified on chromosomes 2HL and 4HL associated with FHB and/or DON were not associated with heading date or plant height. Two novel loci associated with grain zinc concentration were identified on chromosomes 4HS and 6HL. For kernel weight, a known QTL region on chromosome 2HL was detected.
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    Identification of new resistance loci to African stem rust race TTKSK in tetraploid wheats based on linkage and genome-wide association mapping
    (Frontiers in Plant Science, 2015-12-09) Laido, Giovanni; Panio, Giosue; Marone, Daniela; Russo, Maria A; Ficco, Donatella B. M.; Giovaniello, Valentina; Cattivelli, Luigi; Steffenson, Brian; De Vita, Pasquale; Mastrangelo, Anna M
    Stem rust, caused by Puccinia graminis Pers. f. sp. tritici Eriks. and E. Henn. (Pgt), is one of the most destructive diseases of wheat. Races of the pathogen in the “Ug99 lineage” are of international concern due to their virulence for widely used stem rust resistance genes and their spread throughout Africa. Disease resistant cultivars provide one of the best means for controlling stem rust. To identify quantitative trait loci (QTL) conferring resistance to African stem rust race TTKSK at the seedling stage, we evaluated an association mapping (AM) panel consisting of 230 tetraploid wheat accessions under greenhouse conditions. A high level of phenotypic variation was observed in response to race TTKSK in the AM panel, allowing for genome-wide association mapping of resistance QTL in wild, landrace, and cultivated tetraploid wheats. Thirty-five resistance QTL were identified on all chromosomes, and seventeen are of particular interest as identified by multiple associations. Many of the identified resistance loci were coincident with previously identified rust resistance genes; however, nine on chromosomes 1AL, 2AL, 4AL, 5BL, and 7BS may be novel. To validate AM results, a biparental population of 146 recombinant inbred lines was also considered, which derived from a cross between the resistant cultivar “Cirillo” and susceptible “Neodur.” The stem rust resistance of Cirillo was conferred by a single gene on the distal region of chromosome arm 6AL in an interval map coincident with the resistance gene Sr13, and confirmed one of the resistance loci identified by AM. A search for candidate resistance genes was carried out in the regions where QTL were identified, and many of them corresponded to NBS-LRR genes and protein kinases with LRR domains. The results obtained in the present study are of great interest as a high level of genetic variability for resistance to race TTKSK was described in a germplasm panel comprising most of the tetraploid wheat sub-species.
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    Misfits of wheat stem rust resistance-­‐ Unusual solutions to a consistent problem
    (2016-12) Briggs, Jordan
    Rust fungi include some of the most economically damaging pathogens of wheat. They are notorious for their ability to quickly spread in susceptible host populations and greatly reduce grain yield potential and quality when managed improperly. Puccinia graminis f. sp. tritici (Pgt), the causal agent of wheat stem rust, can cause yield losses exceeding 50%. Stem rust is controlled in the U.S.A. using several methods including the introduction of genetic resistance, selection for earlier maturing varieties, removal of the alternate host Berberis vulgaris, and the application of fungicides. Subsequently, epidemics of stem rust causing greater than 10% yield losses have not been observed in the U.S.A. since the mid 1950’s. Together, removal of B. vulgaris from wheat growing regions and the introduction of genetic resistance have accounted for much of the control of stem rust. Genetic resistance remains the dominant method of controlling stem rust in regions where removing B. vulgaris is not applicable. In more recent years, races of Pgt have been identified that overcome most widely deployed resistance genes. In 1999 race TTKSK was identified in Uganda that overcame stem rust resistance gene Sr31. Following deployment of Sr24 in Kenya, further selection for virulence resulted in the identification of race TTKST, then TTTSK (Sr36 virulence), and more recently TTKTT and TTKTK (SrTmp virulence). Major resistance genes have continually proven to not provide a durable form of resistance to wheat stem rust. Some resistance genes however have proven the test of time and remain effective to date. These resistance genes include Sr2, Lr34, Lr46, and Lr67. Each gene functions in an additive, minor-effect, and in some cases recessive manner, atypical of standard major genes, and provides and/or enhances resistance to multiple diseases including stem rust, leaf rust, stripe rust, and powdery mildew. Additionally Lr34 and Lr67 do not have the NB-LRR protein domains consistent with major genes. Durable genetic resistance to stem rust may require sources of resistance that deviate from standard mechanisms. This dissertation describes such sources of resistance. SrTm4 is a major gene identified in Triticum monococcum that functions in a recessive manner, is broadly effective, and elicits a mesothetic (intermediate-effect) infection type. The adult plant resistance observed in ‘Morocho Blanco’ was found to have two underlying QTL, Qsr.cdl.2BS.2 and Qsr.cdl.6AS.1. These two loci comprise much of the adult plant resistance in ‘Morocho Blanco’ and exhibit interactions with environment or pathogen race. The Sr12 mutants created in this dissertation were made to characterize the disease reducing capabilities of Sr12: a recessive, race specific major gene that co-locates with adult plant resistance to Sr12 virulent races. Lastly, this dissertation also describes the identification of putative susceptibility genes for rust pathogens in barley, maize, soybean, and Brachypodium distachyon. The putative susceptibility gene in B. distachyon was tested with a T-DNA insertion mutant and exhibits enhanced rust resistance, however, may be linked to changes in overall plant growth and development. Each source of rust resistance defies standard systems of characterization and includes some traits that are less desirable along with their resistance capabilities, for example: unstable expression due to environmental interactions, race specificity, or recessive gene action. However, the benefit of these sources of stem rust resistance may compensate for their less desirable traits.
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    New resistance in old places: resistance to the Ug99 race group of Puccinia graminis f. sp. tritici in wheat intra/inter-generic hybrids and historic germplasm
    (2015-01) Kielsmeier-Cook, Joshua
    Wheat stem rust caused by the rust fungus, Puccinia graminis f. sp. tritici, threatens global wheat (Triticum aestivum) production. New races originating in Eastern Africa have overcome many existing stem rust resistance genes. The W. J. Sando collection of wheat intra/inter-generic hybrids is a valuable source of stem rust resistance. The entire collection was characterized for seedling stem rust resistance to 8 races of the stem rust pathogen and cytogenetic analysis was performed on select lines. Several accessions are postulated to contain new sources of resistance. Full screening results are displayed in Supplementary Table S1 and the pedigrees of 29 resistant lines are displayed in Supplementary Table S2. South African accession PI 410954 displayed strong resistance to stem rust race TTKSK at the seedling stage and under field conditions. The source of new resistance was located and material suitable for integration into modern spring wheat breeding programs was produced.
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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.