Genetic diversity is key to crop improvement. Owing to pervasive genomic structural variation, a single reference genome assembly cannot capture the full complement of sequence diversity of a crop species (known as the ‘pan-genome’1). Multiple high-quality sequence assemblies are an indispensable component of a pan-genome infrastructure. Barley (Hordeum vulgare L.) is an important cereal crop with a long history of cultivation that is adapted to a wide range of agro-climatic conditions2. Here we report the construction of chromosome-scale sequence assemblies for the genotypes of 20 varieties of barley—comprising landraces, cultivars and a wild barley—that were selected as representatives of global barley diversity. We catalogued genomic presence/absence variants and explored the use of structural variants for quantitative genetic analysis through whole-genome shotgun sequencing of 300 gene bank accessions. We discovered abundant large inversion polymorphisms and analysed in detail two inversions that are frequently found in current elite barley germplasm; one is probably the product of mutation breeding and the other is tightly linked to a locus that is involved in the expansion of geographical range. This first-generation barley pan-genome makes previously hidden genetic variation accessible to genetic studies and breeding.
In recent years, so-called ‘lost crops’ have been appraised in a number of reviews, among them Lablab purpureus in the context of African vegetable species. This crop cannot truly be considered ‘lost’ because worldwide more than 150 common names are applied to it. Based on a comprehensive literature review, this paper aims to put forward four theses, (i) Lablab is one of the most diverse domesticated legume species and has multiple uses. Although its largest agro-morphological diversity occurs in South Asia, its origin appears to be Africa. (ii) Crop improvement in South Asia is based on limited genetic diversity. (iii) The restricted research and development performed in Africa focuses either on improving forage or soil properties mostly through one popular cultivar, Rongai, while the available diversity of lablab in Africa might be under threat of genetic erosion. (iv) Lablab is better adapted to drought than common beans (Phaseolus vulgaris) or cowpea (Vigna unguiculata), both of which have been preferred to lablab in African agricultural production systems. Lablab might offer comparable opportunities for African agriculture in the view of global change. Its wide potential for adaptation throughout eastern and southern Africa is shown with a GIS (geographic information systems) approach.
Summary Barley ( Hordeum vulgare L.) is a major cereal grain widely used for livestock feed, brewing malts and human food. Grain yield is the most important breeding target for genetic improvement and largely depends on optimal timing of flowering. Little is known about the allelic diversity of genes that underlie flowering time in domesticated barley, the genetic changes that have occurred during breeding, and their impact on yield and adaptation. Here, we report a comprehensive genomic assessment of a worldwide collection of 895 barley accessions based on the targeted resequencing of phenology genes. A versatile target‐capture method was used to detect genome‐wide polymorphisms in a panel of 174 flowering time‐related genes, chosen based on prior knowledge from barley, rice and Arabidopsis thaliana . Association studies identified novel polymorphisms that accounted for observed phenotypic variation in phenology and grain yield, and explained improvements in adaptation as a result of historical breeding of Australian barley cultivars. We found that 50% of genetic variants associated with grain yield, and 67% of the plant height variation was also associated with phenology. The precise identification of favourable alleles provides a genomic basis to improve barley yield traits and to enhance adaptation for specific production areas.
BackgroundThe dwarfing gene sdw1 has been widely used throughout the world to develop commercial barley varieties. There are at least four different alleles at the sdw1 locus.ResultsMutations in the gibberellin 20-oxidase gene (HvGA20ox2) resulted in multiple alleles at the sdw1 locus. The sdw1.d allele from Diamant is due to a 7-bp deletion in exon 1, while the sdw1.c allele from Abed Denso has 1-bp deletion and a 4-bp insertion in the 5’ untranslated region. The sdw1.a allele from Jotun resulted from a total deletion of the HvGA20ox2 gene. The structural changes result in lower gene expression in sdw1.d and lack of expression in sdw1.a. There are three HvGA20ox genes in the barley genome. The partial or total loss of function of the HvGA20ox2 gene could be compensated by enhanced expression of its homolog HvGA20ox1and HvGA20ox3. A diagnostic molecular marker was developed to differentiate between the wild-type, sdw1.d and sdw1.a alleles and another molecular marker for differentiation of sdw1.c and sdw1.a. The markers were further tested in 197 barley varieties, out of which 28 had the sdw1.d allele and two varieties the sdw1.a allele. To date, the sdw1.d and sdw1.a alleles have only been detected in the modern barley varieties and lines.ConclusionsThe results provided further proof that the gibberellin 20-oxidase gene (HvGA20ox2) is the functional gene of the barley sdw1 mutants. Different deletions resulted in different functional alleles for different breeding purposes. Truncated protein could maintain partial function. Partial or total loss of function of the HvGA20ox2 gene could be compensated by enhanced expression of its homolog HvGA20ox1 and HvGA20ox3. Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-016-0964-4) contains supplementary material, which is available to authorized users.
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