|Mornhinweg, Dolores - Do|
Submitted to: Plant Breeding
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/18/2013
Publication Date: 4/1/2014
Citation: Azhaguvel, P., Mornhinweg, D.W., Vidya-Saraswathi, D., Rudd, J.C., Chekhovskiy, K., Saha, M., Close, T.J., Dahleen, L.S., Weng, Y. 2014. Molecular mapping of greenbug (Schizaphis graminum) resistance gene Rsg1 in barley. Plant Breeding. 133(2):227-233. Interpretive Summary: Greenbug is a serious pest of small grains worldwide and a persistent pest of wheat and barley in the western US, especially in the southern Great Plains. Two single dominant genes for greenbug resistance, Rsg1 and Rsg2, have been reported in barley. All greenbug resistant US barley cultivars have Rsg1 resistance. This research mapped the chromosomal location of Rsg1 to 3HL. Markers identified as closely linked to Rsg1 will be useful for marker assisted selection increasing the efficiency of breeders developing resistant cultivars, and for map-based cloning of Rsg1. A comparative analysis was done to identify collinear genomic regions on Brachypodium, a model species for molecular marker development and isolating orthologous genes. Potential candidate genes were identified which will enhance our understanding of the chromosomal region which contains Rsg1 as well as other resistance genes.
Technical Abstract: The greenbug, Schizaphis graminum (Rondani) is an extremely damaging aphid pest of barley (Hordeum vulgare L., 2n = 2x =14 L.) particularly in the southern Great Plains of the US. The simply inherited, dominant resistance gene Rsg1 is presented in all greenbug-resistant US barley cultivars, including 'Post 90'. In this study, we conducted molecular mapping of Rsg1 using an F2:3 mapping population derived from the greenbug resistant Post 90*4/R015 and susceptible CI2260 inbred lines. Segregation of host responses to biotype E infestation among F2:3 families suggested a single dominant gene that is responsible for greenbug resistance in Post 90*4/R015. Simple sequence repeat markers evenly distributed along seven barley chromosomes were selected for polymorphism screening between the two parental lines and construction of a framework genetic map. Linkage analysis placed the Rsg1 locus to the long arm of chromosome 3H (3HL) flanked by SSR markers Bmag0877 and GBM1420 that were 35 cM away from each other. Polymorphic SNPs in 3HL were identified from an Illumina GoldenGate SNP assay and used for target mapping in the Rsg1 region delimited by the two SSRs. This effort allowed narrowing down Rsg1 to an interval of 8.4 cM. Comparative analysis identified syntenic genomic regions in Brachypodium chromosome 2, in which 37 putative genes were annotated including several NB-LRR type resistance gene homologs as potential candidate genes for the Rsg1 locus of barley. The markers closely linked to Rsg1 should be useful for marker-assisted selection and for map-based cloning of Rsg1. This result also will enhance our understanding of this chromosomal region which contains several other resistance genes.