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The greenbug, Schizaphis graminum ( Rondani) is an extremely damaging aphid pest of barley ( Hordeum vulgare L.) particularly in the southern Great Plains of the USA. The simply inherited, dominant resistance gene Rsg1 is in all greenbug-resistant US barley cultivars. In this study, we conducted molecular mapping of Rsg1 using an F2:3 population derived from a cross between the greenbug-resistant Post 90*4/ R015 and susceptible CI2260 inbred lines. Segregation of host responses to greenbug biotype E infestation confirmed that a single dominant gene is responsible for greenbug resistance in Post 90*4/ R015. Simple sequence repeat ( SSR) markers evenly distributed along the seven barley chromosomes were employed for the construction of a framework genetic map. Linkage analysis placed the Rsg1 locus in the long arm of chromosome 3 H (3 HL) flanked by SSR markers Bmag0877 and GBM1420 that were 35 c M apart. Polymorphic single-nucleotide polymorphism ( SNP) markers in 3 HL were identified from an Illumina Golden Gate SNP assay and used for targeted mapping to locate Rsg1 to an 8.4-cM interval. Comparative analysis identified syntenic genomic regions in Brachypodium distachyon chromosome 2, in which 37 putative genes were annotated including a NB- LRR-type resistance gene homologue that may be a potential candidate gene for the Rsg1 locus of barley. Results from this study offer a starting point for fine mapping and cloning of this aphid resistance gene in barley. [ABSTRACT FROM AUTHOR]

Abstract: Brittle rachis is an important trait to elucidate the domestication process in barley. Brittle rachis in wild barley (Hordeum vulgare ssp. spontaneum (C. Koch.) Thell) is controlled by two dominant complementary genes, Btr1 and Btr2. Cultivated barley (H. vulgare L. ssp. vulgare) lost the brittle rachis character during domestication as a result of mutation at the Btr1 or Btr2 locus. In this study, a high-resolution map of the btr1 locus was constructed using an F2 population of cultivar (cv. ‘Kanto Nakate Gold’)×wild barley (line OUH602). We cloned and sequenced 26 AFLP markers linked with the btr1 and btr2 loci. Ten converted STS markers were located on the short arm of chromosome 3H only, and at least 9 of the 10 STS markers were allelic with their original AFLPs. Efficient conversion of co-dominant STS markers using BAC clones was successful. No suppression of recombination was observed in the btr1 region even though wild barley was used as one of the parents. Initial results of BAC screening confirmed the resolution power of the developed high resolution map. [Copyright &y& Elsevier]