Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 4, 2012
Publication Date: July 1, 2012
Repository URL: http://riley.nal.usda. gov/nal_web/digi/submission.html
Citation: Dahleen, L.S., Bregitzer, P.P., Jackson, E.W., Mornhinweg, D.W. 2012. Association mapping of russian wheat aphid resistance in barley as a method to identify diversity in the National Small Grains Collection. Crop Science. 52:1651-1662. Interpretive Summary: Barley is an important crop for production of feed, food, and beverages. The Russian wheat aphid is a major limitation for producing barley in the western US as aphid infestations, where they occur, cause major yield losses. Pesticide application to control the aphids is costly and has limited effects because the aphid prevents leaf unrolling, which protects the aphid from any spray exposure. So far, only three aphid resistance genes have been identified although 96 resistant barley lines have been identified. ARS researchers in Fargo ND, Aberdeen ID, and Stillwater OK, used genetic mapping techniques to identify new genes in these resistant lines. DNA markers linked to these genes will be used to develop resistant cultivars with a variety of genes that are less likely to be defeated by the aphid. The availability of additional genes for aphid resistance provide better choices for barley breeders to incorporate resistance that will protect barley yield and quality.
Technical Abstract: Russian wheat aphid (RWA, Diuraphis noxia [Kurdjumov]) is an ongoing problem in the western USA. Infestations in barley (Hordeum vulgare L.) cause chlorotic leaf spotting and streaking and prevent unrolling of emerging leaves which trap spikes and severely reduce fertility and grain yield. Resistant or moderately resistant accessions were identified in the National Small Grains Germplasm collection (NSGC), but adapted germplasm--except for lines derived from crosses to resistant accessions-- is susceptible. The objectives of this study were to identify RWA resistance loci and investigate diversity in the NSGC using association mapping. Resistant accessions and susceptible lines were genotyped with DArT markers and phenotyped for RWA feeding responses. A core haplotype at nine markers was identified in most resistant accessions and derived lines but also in susceptible, adapted cultivars. The opposite haplotype was present in susceptible, unadapted accessions. Variability at four additional markers associated with resistance did not sufficiently account for observed phenotypic variability, suggesting variability at loci not detected by this initial analysis. Examining subsets of the data identified another six markers that were associated with the traits. Markers explained up to 73% of the trait variability. RWA resistance was shown to be a complex trait that may depend in part on alleles that were selected during the development of modern cultivars. Multiple loci may be exploited to provide a number of resistance genes for breeding RWA resistant barley cultivars. Association mapping proved useful for surveying genetic diversity in the NSGC.