Validation of rice blast resistance genes in barley using a QTL mapping population and near-isolines

There are prior reports of Pyricularia grisea-the causal agent of blast of rice-causing disease in barley. In order to determine the specificity of this resistance in barley, we extended our previous mapping efforts to include blast isolates from barley and rice grown in Thailand and we assessed two resistance phenotypes: leaf blast (LB) and neck blast (NB). The largest-effect resistance QTL, on chromosome I H, was associated with NB and LB and is located in a region rich in resistance genes, including QTL conferring resistance to stripe rust (incited by Puccinia striiformis f. sp. hordei) and the mildew (Blumeria graminis f. sp. hordei) resistance gene Mla. The LB, NB and mildew resistance alleles trace to one parent (Baronesse) whereas the stripe rust resistance allele traces to the other parent (BCD47) of the mapping population. Baronesse is the susceptible recurrent parent of a set of near-isogenic lines (NILs) for three stripe rust resistance QTL, including one on 1H. Unigene (EST) derived single nucleotide polymorphism haplotypes of these NILs were aligned with the blast mapping population QTL using Mla as an anchor. Baronesse and all NILs without the 1H introgression were resistant to LB and NB. However, two NILs with the I H introgression were resistant to LB and NB. Both are resistant to stripe rust. Therefore, the QTL conferring resistance to stripe rust is separable by recombination from the blast resistance QTL

Genome-wide association mapping of zinc and iron concentration in barley landraces from Ethiopia and Eritrea

Mamo, B.E., Barber, B., Steffenson, B.J., 2014. Genome- wide association mapping of zinc and iron concentration in barley landraces from Ethiopia and Eritrea. J. Cereal Sci. XX, XX-XX.Barley is one of the oldest cultivated crop plants and is a major part of a staple diet in some developing countries. The objectives of this study were to characterize genetic variation in grain zinc and iron concentration and kernel weight, and identify quantitative trait loci (QTL) associated with these traits in barley landraces from Ethiopia/Eritrea using a genome-wide association study (GWAS). Barley landraces were grown under greenhouse and field conditions, characterized for micronutrient concentration and kernel weight, and then genotyped with 7842 single nucleotide polymorphism (SNP) markers. The germplasm exhibited a wide range of variation for these traits with some accessions having high levels of zinc and iron. Heritability values of 0.65 and 0.59, respectively, were obtained for zinc and iron concentrations in grain samples harvested from field trials. One QTL associated with grain zinc concentration was identified in a unique genomic location on the long arm of chromosome 6H. For kernel weight, a known QTL region on the long arm of chromosome 2H was detected. This study demonstrates the existence of high genetic variation for grain zinc and iron concentration in Ethiopian/Eritrean barley landraces and also the utility of GWAS for identifying and mapping QTL underlying micronutrient accumulation

Genetic and molecular characterization of mating type genes in Cochliobolus sativus

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.Steffenson, Brian; Zhong, Shaobin. (2001). Genetic and molecular characterization of mating type genes in Cochliobolus sativus. Retrieved from the University Digital Conservancy, 10.2307/3761751

Effect of incubation time and temperature on the phenotypic expression of rpg4 to Puccinia graminis f. sp. tritici in barley

Canadian Journal of Plant Pathology website: http://www.tandfonline.com/loi/tcjp20To study the effect of incubation time and temperature on the phenotypic expression of rpg4, five barley genotypes with this resistance gene were infected with pathotype QCCJ of Puccinia graminis f. sp. tritici at the seedling stage, then subjected to various times of incubation at either 18-19°C or 27~28°C. Genotypes with rpg4 exhibited low (0, 0;, and 1), mesothetic (e.g. 3-210;, 120;3), and high (3,3) infection types at 18-19°C after initial incubation at 27-28°C for 0-28, 40-76, and 88 or more hours, respectively. A period of 88 or more hours of initial incubation at high temperature rendered the rpg4 resistance completely ineffective against this pathotype of P. g. f. sp. tritici. In contrast, high, mesothetic, and low infection types were found for the same genotypes at 27-28°C after initial incubation at 18-19°C for 0-40, 52-100, and 112 or more hours, respectively. The resistant infection types conferred by rpg4 are apparently established within the first 112 hours after the end of the infection period since subsequent shifts to higher temperature did not result in marked changes in the resistance response. These data indicate the critical importance of maintaining precise temperature control when assessing the infection phenotypes of barley genotypes carrying the stem rust resistance gene rpg4

Receptivity of barley to Puccinia graminis f. sp. tritici

Canadian Journal of Plant Pathology website: http://www.tandfonline.com/loi/tcjp20The receptivity of barley genotypes {Hordeum vulgare) was studied in seedlings and adult plants in the greenhouse and in adult plants in the field to races I13-RTQ and 151-QSH of Puccinia graminis f. sp. tritici. In the greenhouse, significant differences in number of uredia/cm2 of leaf were detected due to the effects of races, host genotypes, and their interaction. The cultivar Hiproly was most receptive (had the most uredia) and 80-TT-29 was least receptive (had the fewest uredia) to both races at both growth stages. With race 151-QSH, genotypes with the T-gene, 80-TT-29 and Manker had low weighted infection types (seedling stage), moderately resistant host responses (adult stage), and lower receptivity (both growth stages) than cultivars lacking this gene. With race 113-RTQ, the T-gene was associated with low receptivity only in 80-TT-29. The data suggest that gene(s) other than the T-gene may confer receptivity to P. graminis f. sp. tritici. The ranking of genotypes and the relative differences in receptivity were similar in seedling and adult plants. In the field, genotypes with the T-gene had mostly moderately resistant reactions and fewer uredia than those without the gene. The significant race x host genotype interaction in this study suggests that receptivity in barley varies due to the specific host-parasite combination

Puccinia coronata var. hordei var. nov. morphology and pathogenicity

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

Identification of Cochliobolus sativus isolates expressing differential virulence on two-rowed barley genotypes from North Dakota

Canadian Journal of Plant Pathology website: http://www.tandfonline.com/loi/tcjp20Severe spot blotch infection was observed in 1990 on several two-row barley breeding lines previously regarded as resistant to Cochliobolus sativus. Studies were conducted to compare the virulence pattern of a C. sativus isolate (ND90Pr) obtained from this two-row breeding nursery with one (ND85F) used in previous disease screening evaluations. Greenhouse and field experiments were performed in 1991 and 1992 at Fargo, ND, using a split plot design with isolate as the main effect. Isolates ND90Pr and ND85F exhibited distinct differential virulence patterns on barley genotypes ND 5883, ND 12437, ND 12720, ND 12721, and Bowman. Isolate ND90Pr displayed high virulence on ND 12720, ND 12721, and Bowman, and low virulence on ND 5883 and ND 12437. In contrast, isolate ND85F was highly virulent on ND 5883 and ND 12437 and weakly virulent on ND 12720, ND 12721, and Bowman. Both isolates expressed low virulence on genotype ND Bl 12, the primary source of resistance to C. sativus in commercial six-row barley germplasm. To incorporate adequate levels of resistance into future two-row barley cultivars, disease evaluations should be made with C. sativus isolates that express the full spectrum of virulence found in North Dakota

Genome-wide association mapping of fusarium head blight resistance and agromorphological traits in barley landraces from Ethiopia and Eritrea

Fusarium head blight (FHB), caused primarily by Fusarium graminearum, is an important disease of barley (Hordeum vulgare L.), and other cereals. In barley, the genetic basis of FHB resistance has been intensively studied through linkage mapping that identified several quantitative trait loci (QTL). However, our understanding and application of these QTL in breeding is still limited due to the complex nature and low-to-moderate heritability of FHB resistance. Previous studies used either breeding lines, unimproved varieties, or germplasm selections. Here, we used association mapping in barley landraces to identify QTL associated with FHB severity, deoxynivalenol (DON) concentration and correlated agromorphological traits. Diverse barley landraces (n = 298) from Ethiopia and Eritrea were evaluated for the traits under field conditions for 2 yr (2011–2012) in Crookston, MN, and genotyped with 7842 single nucleotide polymorphism (SNP) markers. Association mapping analysis using a mixed model corrected for pairwise relatedness between individuals identified one common resistance QTL on barley chromosome 2HL significantly associated with both FHB severity and DON concentration and another one on 4HL associated with DON concentration. The QTL identified on 2HL is associated with the row-type locus Vrs1. Both of these QTL were not significantly associated with heading date or plant height unlike other QTL reported in previous studies. Thus, the resistant accessions carrying these QTL may be used in breeding programs without the confounding effects from these agromorphological traits. Importantly, these QTL could be new alleles preserved in this unique germplasm, and the linked SNP markers found may be useful in marker-assisted introgression of resistance

The rpg4/Rpg5 stem rust resistance locus in barley; resistance genes and cytoskeleton dynamics

Two closely linked resistance genes, rpg4 and Rpg5, conferring resistance to several races of Puccinia graminis, were cloned and characterized. The Rpg5 gene confers resistance to an isolate of Puccinia graminis f. sp. secalis (Pgs), while rpg4 confers resistance to Puccinia graminis f. sp. tritici (Pgt). Rpg5 is a novel gene containing nucleotide binding site-leucine rich repeat domains in combination with a serine threonine protein kinase domain. High-resolution mapping plus allele and recombinant sequencing identified the rpg4 gene, which encodes an actin depolymerizing factor-like protein (ADF2). Resistance against the Pgt races QCCJ, MCCF, TTKSK (aka Ug99) and RCRS requires both Rpg5 and rpg4, while Rpg5 alone confers resistance to Pgs isolate 92-MN-90. The dependency on the actin modifying protein ADF2 indicates cytoskeleton reorganization or redirection plays a role in pathogen-host interactions. Rpg5 may interact with ADF2 to activate or deactivate its function in the resistance response. Alternatively, Rpg5 could initiate signal transduction leading to resistance in response to detecting ADF2 protein modification. Pgt may redirect the actin cytoskeleton by inducing modifications of ADF2. The redirection of actin could possibly enable the pathogen to develop a haustoria-plant cell cytoskeleton interface for acquisition of nutrients