Dr. Brian Steffenson

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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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    Barley stem rust resistance genes: structure and function
    (Plant Genome, 2009-07) Steffenson, Brian; Kleinhofs, Andris; Brueggeman, Robert; Nirmala, Jayaveeramuthu; Zhang, Ling; Mirlohi, Aghafakhr; Druka, Arnis; Rostoks, Nils
    Rusts are biotrophic pathogens that attack many plant species but are particularly destructive on cereal crops. The stem rusts (caused by Puccinia graminis) have historically caused severe crop losses and continue to threaten production today. Barley (Hordeum vulgare L.) breeders have controlled major stem rust epidemics since the 1940s with a single durable resistance gene Rpg1. As new epidemics have threatened, additional resistance genes were identified to counter new rust races, such as the rpg4/Rpg5 complex locus against races QCCJ and TTKSK. To understand how these genes work, we initiated research to clone and characterize them. The Rpg1 gene encodes a unique protein kinase with dual kinase domains, an active kinase, and a pseudokinase. Function of both domains is essential to confer resistance. The rpg4 and Rpg5 genes are closely linked and function coordinately to confer resistance to several wheat (Triticum aestivum L.) stem rust races, including the race TTKSK (also called Ug99) that threatens the world's barley and wheat crops. The Rpg5 gene encodes typical resistance gene domains NBS, LRR, and protein kinase but is unique in that all three domains reside in a single gene, a previously unknown structure among plant disease resistance genes. The rpg4 gene encodes an actin depolymerizing factor that functions in cytoskeleton rearrangement.
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    Rice-barley synteny and its applications to saturation mapping of the barley Rpg1 region
    (Nucleic Acids Research, 1995-07-25) Steffenson, Brian; Kilian, Andrzej; Kudrna, David A.; Kleinhofs, Andris; Yano, Masahiro; Kurata, Nori; Sasaki, Takuji
    In order to facilitate the map-based cloning of the barley stem rust resistance gene Rpg1, we have demonstrated a high degree of synteny at a micro level between the telomeric region of barley chromosome 1P and rice chromosome 6. We have also developed and applied a simple and efficient method for selecting useful probes from large insert genomic YAC and cosmid clones. The gene order within the most terminal 6.5 cM of barley chromosome 1P was compared with the most terminal 2.7 cM of rice chromosome 6. Nine rice probes, previously mapped in rice or isolated from YAC or cosmid clones from this region, were mapped in barley. All, except one, were in synteny with the rice gene order. The exception, probe Y617R, was duplicated in barley. One copy was located on a different chromosome and the other in a non-syntenic position on barley chromosome 1P. The barley probes from this region could not be mapped to rice, but two of them were inferred to be in a syntenic location based on their position on a rice YAC. This work demonstrates the utility of applying the results of genetic and physical mapping of the small genome cereal rice to map-based cloning of interesting genes from large genome relatives.
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    Puccinia coronata var. hordei var. nov. morphology and pathogenicity
    (Mycologia, 1999) Steffenson, Brian; Jin, Y.
    A new variety of Puccinia coronata causing a disease on barley and other gramineous species is described. The fungus is different from other reported forms of P coronata in both morphology and pathogenicity. Its most prominent characters are the elongated teliospore appendages with dichotomous branching and wide pathogenicity on species in the tribe Triticeae, particularly the genus Hordeum. The name of P coronata var. hordei is proposed for the rust fungus. The common name 'crown rust of barley' is proposed for the disease of barley caused by this rust fungus. Results of inoculation indicated that P coronata var. hordei is pathogenic on species of Aegilops, Agropyron, Elymus, Elytrigia, Leymus, Pascopyrum, Psathyrostachys, Secale, and Triticum in the tribe Triticeae, and some species of Brachypodium, Bromus, Festuca, and Lolium in the tribe Poeae, and Phalaris in the tribe Aveneae. In the northern Great Plains of the USA, the following native and introduced gramineous species were found naturally infected by P coronata var. hordei: Bromus tectorum, Elymus canadensis, E. trachycaulus, E. virginicus, Elytrigia intermedia, E. repens, Hordeum jubatum, H. vulgare, Leymus angustus, L. cinerius, L. dahuricus, L. racemosus, Pascopyrum smithii, Psathyrostachys juncea, and Secale cer- eale.
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    Genetic and molecular characterization of mating type genes in Cochliobolus sativus
    (Mycologia, 2001-09-01) Steffenson, Brian; Zhong, Shaobin
    Genetic and molecular approaches were used to characterize the mating type (MAT) genes in Cochliobolus sativus. One hundred and four ascospore progeny derived from a cross of C. sativus isolates ND93-1 (MAT-1) X ND9OPr (MAT-2) were backcrossed with their parents to determine mating type, but only five progeny produced pseudothecia with asci and/or ascospores. When degenerate primers from the conserved high mobility group (HMG) protein domain encoded by the MAT-2 gene in Cochliobolus species were used in polymerase chain reaction (PCR) with genomic DNA of C. sativus as templates, an amplicon of predicted size was amplified only from MAT-2 isolates. The presence of a MAT-2 homolog in these MAT-2 isolates was confirmed by Southern hybridization with the HMG box as a probe. Additionally, the presence or absence of the HMG homolog in the progeny segregated in a 1:1 ratio, as expected for the single gene control of mating type. Using primers based on the conserved regions at the 5' and 3' flanks of the idiomorphs in the MAT genes of other Cochliobolus species, the full-length MAT-1 and MAT-2 idiomorphs were cloned by PCR from C. sativus isolates ND93-1 and ND9OPr, respectively. DNA sequence analysis indicated that these two idiomorphs are organized in a manner similar to their respective counterparts in other Cochliobolus species. DNA hybridization and PCR amplification analysis of 54 field isolates of C. sativus collected worldwide showed that both mating types exist in populations round the world. The low frequency of successful backcrosses of progeny to parents in the ND93-1 X ND9OPr cross, combined with the fact that many crosses between isolates of opposite mating type are unsuccessful, suggests that genetic factors other than MAT genes affect the fertility of the fungus.
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    Registration of ‘Rasmusson’ barley
    (Journal of Plant Registrations, 2010-09) Steffenson, Brian; Smith, K.P.; Rasmusson, D.C.; Schiefelbein, E.; Wiersma, J.J.; Wiersma, J.V.; Budde, A.; Dill-Macky, R.
    ‘Rasmusson’ (Reg. No. CV-345, PI 658495) is a spring, six-rowed, malting barley (Hordeum vulgare L.) released by the Minnesota Agricultural Experiment Station in January 2008. It was named after Donald Rasmusson, who worked as a barley breeder at the University of Minnesota from 1958 to 2000. Rasmusson has the pedigree M95/‘Lacey’ and is the product of advanced cycle breeding derived from crosses among elite breeding lines within the University of Minnesota breeding program. Rasmusson was released based on its superior yield performance across the Upper Midwest of the United States and surrounding regions in Canada and favorable malting quality, in particular, high malt extract. Rasmusson is resistant to spot blotch [caused by Cochliobolus sativus (Ito and Kuribayashi) Drechs. ex Dastur] and the prevalent races of stem rust (caused by Puccinia graminis Pers.: Pers. f. sp. tritici Erikss. & E. Henn).
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    Registration of ‘Quest’ spring malting barley with improved resistance to Fusarium head blight
    (Journal of Plant Registrations, 2013-01-25) Steffenson, Brian; Smith, K.P.; Budde, A.; Dill-Macky, R.; Rasmusson, D.C.; Schiefelbein, E.; Wiersma, J.J.; Wiersma, J.V.; Zhang, B.
    ‘Quest’ (Reg No. CV-348, PI 663183) is a spring, six-rowed, malting barley (Hordeum vulgare L.) released by the Minnesota Agricultural Experiment Station in January 2010 on the basis of its improved resistance to Fusarium head blight [FHB; caused by Fusarium graminearum Schwabe; teleomorph Gibberella zeae (Schwein) Petch]. Quest was developed over three breeding cycles of selection for yield, malting quality, and FHB resistance. Disease resistance traces to the Midwest cultivar MNBrite and the two-rowed accession from China Zhedar1. Quest has about half the level of disease and about 40% less of the associated mycotoxin, deoxynivalenol, compared to the historically important cultivar in the region ‘Robust’. Quest is similar in yield to the current dominant varieties in the region and was approved as a malting variety by the American Malting Barley Association.
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    Analysis of ergosterol in single kernel and ground grain by gas chromatography-mass spectrometry
    (Journal of Agricultural and Food Chemistry, 2006-05-11) Steffenson, Brian; Dong, Yanhong; Mirocha, Chester J
    A method for analyzing ergosterol in a single kernel and ground barley and wheat was developed using gas chromatography−mass spectrometry (GC-MS). Samples were saponified in methanolic KOH. Ergosterol was extracted by “one step” hexane extraction and subsequently silylated by N-trimethylsilylimidazole/trimethylchlorosilane (TMSI/TMCS) reagent at room temperature. The recoveries of ergosterol from ground barley were 96.6, 97.1, 97.1, 88.5, and 90.3% at the levels of 0.2, 1, 5, 10, and 20 μg/g (ppm), respectively. The recoveries from a single kernel were between 93.0 and 95.9%. The precision (coefficient of variance) of the method was in the range 0.8−12.3%. The method detection limit (MDL) and the method quantification limit (MQL) were 18.5 and 55.6 ng/g (ppb), respectively. The ergosterol analysis method developed can be used to handle 80 samples daily by one person, making it suitable for screening cereal cultivars for resistance to fungal infection. The ability for detecting low levels of ergosterol in a single kernel provides a tool to investigate early fungal invasion and to study mechanisms of resistance to fungal diseases.
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    Identification and mapping of a leaf rust resistance gene in barley line Q21861
    (Genome, 1997) Steffenson, Brian; Borovkova, I.G.; Jin, Y.; Kilian, A.; Blake, T.K.; Kleinhofs, A.
    Barley line Q21861 possesses an incompletely dominant gene (RphQ) for resistance to leaf rust caused by Puccinia hordei. To investigate the allelic and linkage relations between RphQ and other known Rph genes, F2 populations from crosses between Q21861 and donors of Rph1 to Rph14 (except for Rph8) were evaluated for leaf rust reaction at the seedling stage. Results indicate that RphQ is either allelic with or closely linked to the Rph2 locus. A doubled haploid population derived from a cross between Q21861 and SM89010 (a leaf rust susceptible line) was used for molecular mapping of the resistance locus. Bulked segregant analysis was used to identify markers linked to RphQ, using random amplified polymorphic DNAs (RAPDs), restriction fragment length polymorphisms (RFLPs), and sequence tagged sites (STSs). Of 600 decamer primers screened, amplified fragments generated by 9 primers were found to be linked to the RphQ locus; however, only 4 of them were within 10 cM of the target. The RphQ locus was mapped to the centromeric region of chromosome 7, with a linkage distance of 3.5 cM from the RFLP marker CDO749. Rrn2, an RFLP clone from the ribosomal RNA intergenic spacer region, was found to be very closely linked with RphQ, based on bulked segregant analysis. An STS marker, ITS1, derived from Rrn2, was also closely linked (1.6 cM) to RphQ.
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    Sequence analysis of a rice BAC covering the syntenous barley Rpg1 region
    (Genome, 1999) Steffenson, Brian; Han, F.; Kilian, A.; Chen, J.P.; Kudrna, D.; Yamamoto, K.; Matsumoto, T.; Sasaki, T.; Kleinhofs, A.
    In the course of map-based cloning of the barley stem rust resistance gene Rpg1, we identified a rice bacterial artificial chromosome (BAC) containing the Rpg1 flanking markers. Based on the excellent gene order colinearity between barley and rice in this region, we expected that this rice BAC would contain the barley Rpg1 homologue. In order to identify the putative rice homologue, we sequenced ca. 35 kb of the rice BAC at random and then an additional 33 kb of contiguous sequence between the two most closely spaced Rpg1 flanking markers. Sequence analysis revealed a total of 15 putative genes, 5 within the 33-kb contiguous region. A rice Rpg1 homologue was not identified, although a gene encoding a hypothetical polypeptide with similarity to a membrane protein could not be eliminated as a candidate. Surprisingly, four of the genes identified in the 33-kb contiguous rice sequence showed a high degree of similarity with genes on Arabidopsis chromosome 4. The genome regions harboring these genes showed some relatedness, but many rearrangements were also evident. These data suggest that some genes have remained linked even over the long evolutionary separation of Arabidopsis and rice, as has also been reported for mammals and invertebrates.
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    Identification and chromosomal location of major genes for resistance to Pyrenophora teres in a doubled-haploid barley population
    (Genome, 2006) Steffenson, Brian; Friesen, T.L.; Faris, J.D.; Lai, Z.
    Net blotch, caused by Pyrenophora teres, is one of the most economically important diseases of barley worldwide. Here, we used a barley doubled-haploid population derived from the lines SM89010 and Q21861 to identify major quantitative trait loci (QTLs) associated with seedling resistance to P. teres f. teres (net-type net blotch (NTNB)) and P. teres f. maculata (spot-type net blotch (STNB)). A map consisting of simple sequence repeat (SSR) and amplified fragment length polymorphism (AFLP) markers was used to identify chromosome locations of resistance loci. Major QTLs for NTNB and STNB resistance were located on chromosomes 6H and 4H, respectively. The 6H locus (NTNB) accounted for as much as 89% of the disease variation, whereas the 4H locus (STNB resistance) accounted for 64%. The markers closely linked to the resistance gene loci will be useful for marker-assisted selection.Key words: disease resistance, Drechslera teres, molecular markers.
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    Genetic architecture of quantitative trait loci associated with morphological and agronomic trait differences in a wild by cultivated barley cross
    (Genome, 2007) Steffenson, Brian; Gyenis, L.; Yun, S.J.; Smith, K.P.; Bossolini, E.; Sanguineti, M.C.; Muehlbauer, G.J.
    Hordeum vulgare subsp. spontaneum is the progenitor of cultivated barley (Hordeum vulgare L.). Domestication combined with plant breeding has led to the morphological and agronomic characteristics of modern barley cultivars. The objective of this study was to map the genetic factors that morphologically and agronomically differentiate wild barley from modern barley cultivars. To address this objective, we identified quantitative trait loci (QTLs) associated with plant height, flag leaf width, spike length, spike width, glume length in relation to seed length, awn length, fragility of ear rachis, endosperm width and groove depth, heading date, flag leaf length, number of tillers per plant, and kernel color in a Harrington/OUH602 advanced backcross (BC2F8) population. This population was genotyped with 113 simple sequence repeat markers. Thirty QTLs were identified, of which 16 were newly identified in this study. One to 4 QTLs were identified for each of the traits except glume length, for which no QTL was detected. The portion of phenotypic variation accounted for by individual QTLs ranged from about 9% to 54%. For traits with more than one QTL, the phenotypic variation explained ranged from 25% to 71%. Taken together, our results reveal the genetic architecture of morphological and agronomic traits that differentiate wild from cultivated barley.
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    Development of a genetic linkage map for Sharon goatgrass (Aegilops sharonensis) and mapping of a leaf rust resistance gene
    (Genome, 2013) Steffenson, Brian; Olivera, P.D.; Kilian, A.; Wenzl, P.
    Aegilops sharonensis (Sharon goatgrass), a diploid wheat relative, is known to be a rich source of disease resistance genes for wheat improvement. To facilitate the transfer of these genes into wheat, information on their chromosomal location is important. A genetic linkage map of Ae. sharonensis was constructed based on 179 F2 plants derived from a cross between accessions resistant (1644) and susceptible (1193) to wheat leaf rust. The linkage map was based on 389 markers (377 Diversity Arrays Technology (DArT) and 12 simple sequence repeat (SSR) loci) and was comprised of 10 linkage groups, ranging from 2.3 to 124.6 cM. The total genetic length of the map was 818.0 cM, with an average interval distance between markers of 3.63 cM. Based on the chromosomal location of 115 markers previously mapped in wheat, the four linkage groups of A, B, C, and E were assigned to Ae. sharonensis (Ssh) and homoeologous wheat chromosomes 6, 1, 3, and 2. The single dominant gene (designated LrAeSh1644) conferring resistance to leaf rust race THBJ in accession 1644 was positioned on linkage group A (chromosome 6Ssh) and was flanked by DArT markers wpt-9881 (at 1.9 cM distal from the gene) and wpt-6925 (4.5 cM proximal). This study clearly demonstrates the utility of DArT for genotyping uncharacterized species and tagging resistance genes where pertinent genomic information is lacking.
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    Introgression of leaf rust and stripe rust resistance from Sharon goatgrass (Aegilops sharonensis Eig) into bread wheat (Triticum aestivum L.)
    (Genome, 2014) Steffenson, Brian; Millet, E.; Manisterski, J.; Ben-Yehuda, P.; Distelfeld, A.; Deek, J.; Wan, A.; Chen, X.
    Leaf rust and stripe rust are devastating wheat diseases, causing significant yield losses in many regions of the world. The use of resistant varieties is the most efficient way to protect wheat crops from these diseases. Sharon goatgrass (Aegilops sharonensis or AES), which is a diploid wild relative of wheat, exhibits a high frequency of leaf and stripe rust resistance. We used the resistant AES accession TH548 and induced homoeologous recombination by the ph1b allele to obtain resistant wheat recombinant lines carrying AES chromosome segments in the genetic background of the spring wheat cultivar Galil. The gametocidal effect from AES was overcome by using an “anti-gametocidal” wheat mutant. These recombinant lines were found resistant to highly virulent races of the leaf and stripe rust pathogens in Israel and the United States. Molecular DArT analysis of the different recombinant lines revealed different lengths of AES segments on wheat chromosome 6B, which indicates the location of both resistance genes.
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    Infection of gramineous species by Barley Yellow Dwarf Viruses in California
    (Crop Science, 1990) Steffenson, Brian; Griesbach, J.A.; Brown, M.P.; Falk, B.W.; Webster, R.K.
    Barley yellow dwarf viruses (BYDVs) continue to cause losses California cereal production. In some parts of the USA, native grasses have been implicated as reservoirs of BYDVs. This study examines the potential of native and irrigated pasture grasses as sources of BYDV inoculum in California. Theffects of both natural and natural plus supplemental inoculum were examined in field trials over two growing seasons using a completely randomized design. Results were assessed by enzyme-linked immunosorbent assay (ELISA) and verified with controlled greenhouse vector transmission trials. Thirty-seven of 56 species of cool-season grasses were infected by either PAV, MAV, or RPV isolates of the BYDVs. Of the BYDV-infected grasses, only 38% displayed symptoms typically seen in infected oat (Avena sativa L.) and barley (Hordeum vulgare L.), while the others were asymptomatic. None of the plants from seven species of Leymus, nor plants from the majority of Elymus and Elytrigia species, had detectable BYDV infections, even though they supported aphid vector populations. A survey of common grasses from irrigated pastures showed that plants from 6 of 10 species were infected by either the PAV, MAV, or RPV isolates of BYDVs. The incidence of MAV, PAV, and RPV BYDVs were roughly equivalent for the cool-season grasses, but were highly skewed toward PAV in the irrigated pasture survey. Both cool-season and irrigated warm-season pasture grasses have the potential to serve as BYDV reservoirs in California.
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    Linkage between the Rpg1 gene for stem rust resistance and the f5 locus on barley chromosome
    (Crop Science, 1993) Steffenson, Brian; Jin, Yue; Franckowiak, Jerome D
    Linkage studies can expedite the transfer of agronomically important genes in breeding programs. A study was conducted to determine the linkage relationship between loci segregating for stem rust (Puccinia graminis Pers.:Pers. f. sp. tritici Eriks. & E. Henn.) resistance (Rpg1) and a chlorina mutant (f5), and to confirm the linkage among Rpg1, br1 (brachytic) and fc (chlorina seedling). ‘Bowman’ barley (Hordeum vulgare L.) was crossed to genetic stocks possessing br1, fc, and f5, respectively. Estimates of linkage distances were 9.6 ± 1.4% between Rpg1 and br1, 13.6 ± 1.8% between Rpg1 and fc, and 25.9 ± 2.6% between Rpg1 and f5. The linkage between Rpg1 and f5 was established.
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    Sources of resistance to pathotype QCC of Puccinia graminis f. sp. tritici in barley
    (Crop Science, 1994) Steffenson, Brian; Jin, Yue; Fetch, Thomas G.
    The occurrence of a wheat stem rust (Puccinia graminis Pers.:Pers. f. sp. tritici Eriks. & E. Henn.) pathotype (Pgt-QCC) with virulence for the Rpg1 gene in barley (Hordeum vulgare L.) necessitated the search for resistant barley germplasm. From preliminary screenings of over 18 000 barley accessions, 13 lines were identified as possessing resistance to pathotype QCC: ‘Diamond’, ‘Hietpas 5’, Q21861, PC 11, PC 84, PC 249, PC 250, CI 5541, PI 452406, PI 452421, PI 477843, PI 477854, and PI 477860. This study was conducted to further characterize the reaction of the selected lines to pathotype QCC. The reaction was assessed by evaluating infection types at the seedling stage and infection responses at the adult plant stage in the greenhouse, and by evaluating disease severity and infection responses at the adult plant stage in the field compared to susceptible cultivars. Most lines exhibited low to intermediate infection types at the seedlings stage and moderately resistant to moderately susceptible infection responses at the adult plant stage in the greenhouse experiments. Among the selected lines, Q21861 exhibited the highest level of resistance at both the seedling and adult plant stages. These lines may provide an adequate level of resistance to pathotype QCC for cultivar development.
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    Regions of the genome that affect agronomic performance in two-row barley
    (Crop Science, 1996) Steffenson, Brian; Tinker, N.A.; Mather, D.E.; Rossnagel, B.G.; Kasha, K.J.; Kleinhofs, A.; Hayes, P.M.; Falk, D.E.; Ferguson, T.; Shugar, L.P.; Legge, W.G.; Irvine, R.B.; Choo, T.M.; Briggs, K.G.; Ullrich, S.E.; Franckowiak, J.D.; Blake, T.K.; Graf, R.J.; Dofing, S.M.; Saghai Maroof, M.A.; Scoles, G.J.; Hoffman, D.; Dahleen, L.S.; Kilian, A.; Chen, F.; Biyashev, R.M.; Kudrna, D.A.
    Quantitative trait locus (QTL) main effects and QTL by environment (QTL × E) interactions for seven agronomic traits (grain yield, days to heading, days to maturity, plant height, lodging severity, kernel weight, and test weight) were investigated in a two-row barley (Hordeum vulgare L.) cross, Harrington/TR306. A 127-point base map was constructed from markers (mostly RFLP) scored in 146 random double-haploid (DH) lines from the Harrington/TR306 cross. Field experiments involving the two parents and 145 random DH lines were grown in 1992 and/or 1993 at 17 locations in North America. Analysis of QTL was based on simple and composite interval mapping. Primary QTL were declared at positions where both methods gave evidence for QTL. The number of primary QTL ranged from three to six per trait, collectively explaining 34 to 52% of the genetic variance. None of these primary QTL showed major effects, but many showed effects that were consistent across environments. The addition of secondary QTL gave models that explained 39 to 80% of the genetic variance. The QTL were dispersed throughout the barley genome and some were detected in regions where QTL have been found in previous studies. Eight chromosome regions contained pleiotropic loci and/or linked clusters of loci that affected multiple traits. One region on chromosome 7 affected all traits except days to heading. This study was an intensive effort to evaluate QTL in a narrow-base population grown in a large set of environments. The results reveal the types and distributions of QTL effects manipulated by plant breeders and provide opportunities for future testing of marker-assisted selection.
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    Registration of ‘Foster’ barley
    (Crop Science, 1997) Steffenson, Brian; Horsley, R.D.; Franckowiak, J.D.; Schwarz, P.B.
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    Mapping of disease resistance loci in barley based on visual assessment of naturally occurring symptoms
    (Crop Science, 1998) Steffenson, Brian; Spaner, D.; Shugar, L.P.; Choo, T.M.; Falak, I.; Briggs, K.G.; Legge, W.G.; Falk, D.E.; Ullrich, S.E.; Tinker, N.A.; Mather, D.E.
    Using field-scored data of disease severity under natural infestation, we mapped loci affecting resistance to powdery mildew (Blumeria graminis DC f. sp. hordei Ém. Marchal), leaf rust (Puccinia hordei Otth.), stem rust (Puccinia graminis f. sp. tritici Eriks. & E. Henn.), scald [Rhynchosporium secalis (Oudem.) J.J. Davis], and net blotch (Pyrenophora teres Drechs.). The mapping population included parents and doubled-haploid progeny of the two-row barley cross Harrington/TR306. Resistance was affected by two to five loci, explaining 8 to 45% of the phenotypic variance, per disease. All chromosomes, except chromosome 5 (1H), contained regions with at least one disease resistance locus. One region on chromosome 4 (4H) contributed to resistance to stem rust, scald, and net blotch. This region has previously been reported to affect days to heading and maturity. Two known resistance genes in the population, Rpgl and M1g, were mapped to within 3 centimorgans (cM) of their previously estimated genomic locations by simple interval mapping of the field-scored data. This indicates that the genomic positions of disease resistance genes can be estimated accurately with simple interval mapping, even on the basis of field-scored data.