Agronomic Characteristics, Malt Quality, and Disease Resistance of Barley Germplasm Lines with Partial Fusarium Head Blight Resistance

Fusarium head blight (FHB), incited by Fusarium graminearum Schwabe, has caused devastating losses in both yield and quality of barley (Hordeum vulgare L.) produced in the northern Great Plains from 1993 to 2003. Thirty-five barley germplasmlines with partial resistance to FHB have been identified in exotic and unadapted germplasm lines. Little is known about their agronomic characteristics, malt quality, and reaction to other diseases as compared to adapted cultivars. This information is needed so barley breeders can make informed decisions when planning crosses involving the resistant germplasm lines. The objective of this study was to compare the agronomic performance, malt quality, and disease reaction of barley germplasm lines with partial FHB resistance to cultivars grown in the northern Great Plains. Agronomic and malting data were collected on the 35 germplasm lines and five check cultivars grown in five environments in North Dakota from 1998 to 2000. Data for FHB severity and deoxynivalenol (DON, a mycotoxin produced by F. graminearum) accumulation were obtained for the same 40 entries grown in FHB-epidemic nurseries in North Dakota from 1997 to 1999. Seedling responses to foliar pathogens common in the northern Great Plains were determined in the greenhouse during fall 1997. None of the FHB-resistant barley germplasm lines had acceptable malt quality for all traits. Kernel plumpness, grain protein concentration, and malt extract were the traits impacted most severely. The FHB-resistant barley germplasm lines headed significantly later than the adapted barley cultivars. Most FHB-resistant germplasm lines were susceptible to the common foliar diseases of the northern Great Plains. At least four cycles of breeding will probably be necessary to develop FHB-resistant germplasm lines acceptable to producers and the malting and brewing industry

Analysis of ergosterol in single kernel and ground grain by gas chromatography-mass spectrometry

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

Heritability of Fusarium Head Blight Resistance and Deoxynivalenol Accumulation from Barley Accession CIho 4196

Fusarium head blight (FHB), incited by Fusarium graminearum Schwabe [telomorph Gibberella zea (Schwein)], has caused devastating losses to yield and quality of barley (Hordeum vulgare L.) produced in the upper U.S. Midwest from 1993 to 2000. Design of an efficient breeding strategy for developing FHB resistant cultivars is dependent on knowing (i) the heritability of FHB resistance and accumulation of deoxynivalenol (DON), a mycotoxin contaminant produced by F. graminearum and (ii) the correlated response of other traits during selection for reduced FHB. We conducted field studies in FHB disease nurseries using F4:5 and F4:6 families from the cross between the FHB susceptible six-rowed cultivar Foster and the resistant two-rowed accession CIho 4196 to gain knowledge in the areas listed above. Heritability of FHB severity and DON accumulation was 0.65 and 0.46, respectively. A moderately strong positive association between FHB severity and DON accumulation was observed (r = 0.62). FHB severity and DON accumulation were negatively associated with plant height, days to heading, spike angle, and spike density. The selection differentials calculated between the top F4:6 families selected for low FHB severity and the unselected F4:5 families were moderately high for FHB severity, DON accumulation, and days to heading. Less than 14% of the selected lines had six-rowed spikes. No difference in plant height was observed between the selected and unselected families. Thus, development of FHB resistant lines with acceptable DON accumulation and days to heading is obtainable. However, because no lines were as short as Foster, development of FHB resistant plants with acceptable plant height from a cross using CIho 4196 as a parent will be difficult

Genome-Wide Association Study Identifies Two Loci for Stripe Rust Resistance in a Durum Wheat Panel from Iran

Stripe rust (Puccinia striiformis f. sp. tritici (Pst)) is one of the most devastating fungal diseases of durum wheat (Triticum turgidum L. var. durum Desf.). Races of Pst with new virulence combinations are emerging more regularly on wheat-growing continents, which challenges wheat breeding for resistance. This study aimed to identify and characterize resistance to Pst races based on a genome-wide association study. GWAS is an approach to analyze the associations between a genome-wide set of single-nucleotide polymorphisms (SNPs) and target phenotypic traits. A total of 139 durum wheat accessions from Iran were evaluated at the seedling stage against isolates Pstv-37 and Pstv-40 of Pst and then genotyped using a 15K SNP chip. In total, 230 significant associations were identified across 14 chromosomes, of which 30 were associated with resistance to both isolates. Furthermore, 17 durum wheat landraces showed an immune response against both Pst isolates. The SNP markers and resistant accessions identified in this study may be useful in programs breeding durum wheat for stripe rust resistance

Identification of QTLs Associated with Fusarium Head Blight Resistance in Barley Accession CIho 4196

Fusarium head blight (FHB), incited by Fusarium graminearum Schwabe [teleomorph Gibberella zea (Schwein)], reduces quality of harvested barley (Hordeum vulgare L.) because of blighted kernels and the presence of deoxynivalenol (DON), a mycotoxin produced by the pathogen. CIho 4196, a two-rowed type, is one of the most resistant accessions known in barley; however, it possesses many undesirable agronomic traits. To better understand the genetics of reduced FHB severity and DON accumulation conferred by CIho 4196, a genetic map was generated using a population of recombinant inbred lines derived from a cross between Foster (a six-rowed malting cultivar) and CIho 4196. Quantitative trait loci (QTL) analyses were performed using data obtained from 10 field environments. The possible associations of resistance QTLs and various agronomic and morphological traits in barley also were investigated. The centromeric region of chromosome 2H flanked by the markers ABG461C and MWG882A (bins 6–10) likely (P\u3c0.001) contains two QTLs contributing to lower FHB severity and plant height, and one QTL each for DON accumulation, days to heading, and rachis node number. The QTL for low FHB severity in the bin 8 region explained from 3 to 9% of the variation, while the QTL in the bin 10 region explained from 17 to 60% of the variation. A QTL for DON accumulation that explained 9 to 14% of the variation was found in the bin 2 region of chromosome 4H. This may represent a new QTL not present in other FHB resistant sources. Resistance QTLs in the bin 8 region and bin 10 region of chromosome 2HL were provisionally designated Qrgz-2H-8 and Qrgz-2H-10, respectively. The QTL for DON accumulation in chromosome 4H was provisionally named QDON-4H-2

Introgression of leaf rust and stripe rust resistance from Sharon goatgrass (Aegilops sharonensis Eig) into bread wheat (Triticum aestivum L.)

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

The barley stem rust-resistance gene Rpg1 is a novel disease-resistance gene with homology to receptor kinases

Stem rust caused by Puccinia graminis f. sp. tritici was among the most devastating diseases of barley in the northern Great Plains of the U.S. and Canada before the deployment of the stem rust-resistance gene Rpg1 in 1942. Since then, Rpg1 has provided durable protection against stem rust losses in widely grown barley cultivars (cvs.). Extensive efforts to clone Rpg1 by synteny with rice provided excellent flanking markers but failed to yield the gene because it does not seem to exist in rice. Here we report the map-based cloning and characterization of Rpg1. A high-resolution genetic map constructed with 8,518 gametes and a 330-kb bacterial artificial chromosome contig physical map positioned the gene between two crossovers ≈0.21 centimorgan and 110 kb apart. The region including Rpg1 was searched for potential candidate genes by sequencing low-copy probes. Two receptor kinase-like genes were identified. The candidate gene alleles were sequenced from resistant and susceptible cvs. Only one of the candidate genes showed a pattern of apparently functional gene structure in the resistant cvs. and defective gene structure in the susceptible cvs. identifying it as the Rpg1 gene. Rpg1 encodes a receptor kinase-like protein with two tandem protein kinase domains, a novel structure for a plant disease-resistance gene. Thus, it may represent a new class of plant resistance genes

Changing the Game: Using Integrative Genomics to Probe Virulence Mechanisms of the Stem Rust Pathogen Puccinia graminis f. sp. tritici

The recent resurgence of wheat stem rust caused by new virulent races of Puccinia graminis f. sp. tritici (Pgt) poses a threat to food security. These concerns have catalyzed an extensive global effort toward controlling this disease. Substantial research and breeding programs target the identification and introduction of new stem rust resistance (Sr) genes in cultivars for genetic protection against the disease. Such resistance genes typically encode immune receptor proteins that recognize specific components of the pathogen, known as avirulence (Avr) proteins. A significant drawback to deploying cultivars with single Sr genes is that they are often overcome by evolution of the pathogen to escape recognition through alterations in Avr genes. Thus, a key element in achieving durable rust control is the deployment of multiple effective Sr genes in combination, either through conventional breeding or transgenic approaches, to minimize the risk of resistance breakdown. In this situation, evolution of pathogen virulence would require changes in multiple Avr genes in order to bypass recognition. However, choosing the optimal Sr gene combinations to deploy is a challenge that requires detailed knowledge of the pathogen Avr genes with which they interact and the virulence phenotypes of Pgt existing in nature. Identifying specific Avr genes from Pgt will provide screening tools to enhance pathogen virulence monitoring, assess heterozygosity and propensity for mutation in pathogen populations, and confirm individual Sr gene functions in crop varieties carrying multiple effective resistance genes. Toward this goal, much progress has been made in assembling a high quality reference genome sequence for Pgt, as well as a Pan-genome encompassing variation between multiple field isolates with diverse virulence spectra. In turn this has allowed prediction of Pgt effector gene candidates based on known features of Avr genes in other plant pathogens, including the related flax rust fungus. Upregulation of gene expression in haustoria and evidence for diversifying selection are two useful parameters to identify candidate Avr genes. Recently, we have also applied machine learning approaches to agnostically predict candidate effectors. Here, we review progress in stem rust pathogenomics and approaches currently underway to identify Avr genes recognized by wheat Sr genes

The low recombining pericentromeric region of barley restricts gene diversity and evolution but not gene expression

The low-recombining pericentromeric region of the barley genome contains roughly a quarter of the genes of the species, embedded in low recombining DNA that is rich in repeats and repressive chromatin signatures. We have investigated the effects of pericentromeric region residency upon the expression, diversity and evolution of these genes. We observe no significant difference in average transcript level or developmental RNA specificity between the barley pericentromeric region and the rest of the genome. In contrast, all of the evolutionary parameters studied here show evidence of compromised gene evolution in this region. First, genes within the pericentromeric region of wild barley show reduced diversity and significantly weakened purifying selection compared to the rest of the genome. Second, gene duplicates (ohnolog pairs) derived from the cereal whole genome duplication event ca. 60MYa have been completely eliminated from the barley pericentromeric region. Third, local gene duplication in the pericentromeric region is reduced by 29% relative to the rest of the genome. Thus, the pericentromeric region of barley is a permissive environment for gene expression but has restricted gene evolution in a sizeable fraction of barley's genes. This article is protected by copyright. All rights reserved