Location: Cereal Crops ResearchTitle: Association mapping of grain hardness, polyphenol oxidase, total phenolics, amylose content, and ß-glucan in US barley breeding germplasm Author
Submitted to: Molecular Breeding
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/8/2014
Publication Date: 5/16/2014
Publication URL: http://handle.nal.usda.gov/10113/59604
Citation: Mohammadi, M., Endelman, J.B., Nair, S., Chao, S., Jones, S.S., Muehlbauer, G.J., Ullrich, S.E., Baik, B.-K., Wise, M.L., Smith, K.P. 2014. Association mapping of grain hardness, polyphenol oxidase, total phenolics, amylose content, and ß-glucan in US barley breeding germplasm. Molecular Breeding. 34:1229-1243. Interpretive Summary: Although principally used for feed and malt, barley also has unique nutritional properties as a food crop. A renewed interest in breeding barley specifically for food end-uses is being driven by increased consumer interest in healthier foods. The objective was to understand the genetic architecture underlying five quality traits that are important for food processing and nutritional benefits, and the extent of genetic variations present among the US barley breeding programs. The five traits investigated included kernel hardness, amylose content, total phenolics, polyphenol oxidase (PPO) activity, and beta-glucan. Kernel hardness can influence the pearling process and flour particle size. Amylose content is important for textural properties of barley food products. Enzymatic activity for PPO and the amount of phenolic compounds affect the color and overall appearance of barley foods and their acceptance by consumers. High beta-glucan content contributes health benefits by lowering cholesterol and decreasing the risk of cardiovascular disease. We used genetic association analysis to evaluate 3,069 spring barley breeding lines from eight U.S. breeding programs, and identified DNA markers and chromosome regions affecting the inheritance of the five quality traits measured. Substantial genetic diversity at the regions influencing food quality traits was found present among the US barley breeding programs. Knowledge of the genetic variations and DNA markers revealed from this study facilitate the development of strategies for food-barley improvement.
Technical Abstract: A renewed interest in breeding barley specifically for food end-uses is being driven by increased consumer interest in healthier foods. We conducted association mapping on physicochemical properties of barley that play a role in food quality and processing including, grain hardness, polyphenol oxidase activity, total phenolics, amylose content, and ß-glucan. We used 3,069 elite spring barley breeding lines from eight U.S. breeding programs and 2,027 SNP markers for association mapping. Population structure was analyzed by using the marker scores and principal component (PC) analysis. The first PC differentiated six-row and two-row breeding lines and the second PC partially separated two-row breeding lines by breeding program. Marker-trait associations were identified using a mixed model that incorporated population structure and kinship using a family-wise Type I error control of FDR = 5%. We detected two previously identified QTL for grain hardness on 2H (near Vrs1) and the telomeric region of 5H along with two novel regions on 4H and 6H. For amylose content, we detected marker-trait associations on 7H from 0.63 cM to 30 cM. We detected a very strong association for polyphenol oxidase on chromosome 2H that co-localized with the two previously mapped polyphenol oxidase genes PPO1 and PPO2. In addition, we detected three novel regions on chromosomes 1H, 3H, and 4H. For total phenolics, we identified three significant regions on 3H, 4H, and 5H. Two regions on 2H and 7H were associated with ß-glucan. The distribution of favorable alleles at these key loci that underpin food quality across the breeding programs suggest several strategies to use markers to improve barley for food uses.