Chromosome-scale assembly of wild barley accession ‘OUH602’

Barley (Hordeum vulgare) was domesticated from its wild ancestral form ca. 10,000 years ago in the Fertile Crescent and is widely cultivated throughout the world, except for in tropical areas. The genome size of both cultivated barley and its conspecific wild ancestor is approximately 5 Gb. High-quality chromosome-level assemblies of 19 cultivated and one wild barley genotype were recently established by pan-genome analysis. Here, we release another equivalent short-read assembly of the wild barley accession ‘OUH602’. A series of genetic and genomic resources were developed for this genotype in prior studies. Our assembly contains more than 4.4 Gb of sequence, with a scaffold N50 value of over 10 Mb. The haplotype shows high collinearity with the most recently updated barley reference genome, ‘Morex’ V3, with some inversions. Gene projections based on ‘Morex’ gene models revealed 46,807 protein-coding sequences and 43,375 protein coding genes. Alignments to publicly available sequences of bacterial artificial chromosome (BAC) clones of ‘OUH602’ confirm the high accuracy of the assembly. Since more loci of interest have been identified in ‘OUH602’, the release of this assembly, with detailed genomic information, should accelerate gene identification and the utilization of this key wild barley accession.

Characterization of RsgWBDC053: A New Greenbug Resistance Gene From Wild Barley (Hordeum Vulgare ssp. Spontaneum)

Greenbug (Schizaphis graminum Rondani) is a destructive insect pest that not only damages plants, but also serves as a vector for many viruses. Host plant resistance is the preferred strategy for managing greenbug. To date, only two greenbug resistance genes, Rsg1 and Rsg2, have been reported in barley, with only the former being deployed in cultivars. To breed cultivars with effective resistance against various greenbug biotypes, additional resistance genes are urgently needed to sustain barley production. Wild barley accession WBDC053 (PI 681777), originating from the Baluchistan region of Pakistan, was previously found to be resistant to several greenbug biotypes. In this study, a recombinant inbred line (RIL) population derived from Weskan × WBDC053 was evaluated for response to greenbug biotype E and genotyped using genotyping by sequencing (GBS). A set of 3,347 high quality GBS-derived single nucleotide polymorphisms (SNPs) were then used to map a greenbug resistance gene in this wild barley accession. Linkage analysis placed the greenbug resistance gene in WBDC053, temporarily designated RsgWBDC053, in a 2.35 Mb interval (0-2,354,645 bp) in the terminal region of the short arm of chromosome 2H. This interval harbors 15 genes with leucine-rich-repeat (LRR) protein domains. An allelism test between WBDC053 carrying RsgWBDC053 and STARS1501B carrying Rsg2 indicated that the former is either allelic or closely linked to the latter. GBS-SNPs 2H_1318811 and 2H_1839499 co-segregated with RsgWBDC053 and were converted to Kompetitive allele specific PCR (KASP) markers, KASP-Rsg053-1 and KASP-Rsg0533-2. The two KASP markers can be used to select for RsgWBDC053, but also have the potential to tag Rsg2 in barley improvement programs.

A novel QTL for Septoria speckled leaf blotch resistance in barley (Hordeum vulgare L.) accession PI 643302 by whole-genome QTL mapping

Septoria speckled leaf blotch (SSLB), caused by Septoria passerinii , is one of the most important foliar diseases of barley ( Hordeum vulgare L.) in North America. The primary problem caused by this disease is substantial yield loss. The objective of this study was to determine the chromosomal location of SSLB resistance genes in the barley accession PI 643302. A recombinant inbred line population was developed from the cross Zhenongda 7/PI 643302. PI 643302 is resistant while Zhenongda 7 is susceptible to SSLB. The population was phenotyped for SSLB resistance in five experiments in the greenhouse. A linkage map comprising 113 molecular markers was constructed and simplified composite interval mapping was performed. Two QTLs, designated QrSp-1H and QrSP-2H, were found. QrSp-1H was found on the short arm of chromosome 1H (1HS) in all five experiments and showed a large effect against SSLB. Based on the location of QrSp-1H, it is likely the SSLB resistance gene Rsp2. The QTL QrSp-2H mapped to the distal region on the long arm of chromosome 2H (2HL), had a smaller effect than QrSp-1H, and was also detected consistently in all five experiments. A QTL for SSLB resistance in the same region on chromosome 2H has not been reported previously in either cultivated or wild barley; thus, QrSp-2H is a new QTL for SSLB resistance in barley.

Comparative analysis of genetic diversity between Qinghai-Tibetan wild and Chinese landrace barley

Fifty-two SSR markers were used to evaluate the genetic diversity of 33 Qinghai-Tibetan wild barley accessions, 56 landraces collected primarily from other parts of China, and 1 Israeli wild barley accession. At the 52 SSR loci, 206 alleles were detected for the 90 accessions, among which 111 were common alleles. The number of alleles per locus ranged from 1 to 9, with an average of 4.0. Polymorphism information content (PIC) values ranged from 0 to 0.856 among all the markers, with an average of 0.547. The PIC value of Qinghai-Tibetan wild barley varied from 0 to 0.813 with an average of 0.543, while in landraces, the markers showed a range of 0 to 0.790 with an average of 0.490. The SSR markers could clearly differentiate the Qinghai-Tibetan wild barley from the landraces. Twenty-four unique alleles were observed in Qinghai-Tibetan wild barley, and the frequency of unique alleles in Qinghai-Tibetan wild barley was about 2.1 times higher than that in the landraces, on average. Five of the 7 chromosomes had more unique alleles in the Qinghai-Tibetan wild barley, but chromosome 2H had more unique alleles in the landraces. The presence of many unique alleles may reflect the adaptation of this barley germplasm to diverse environments and production systems.