Submitted to: Proceedings International Barley Genetics Symposium
Publication Type: Proceedings
Publication Acceptance Date: 7/15/1996
Publication Date: N/A
Interpretive Summary: Plant breeders have trouble selecting for many malting barley characteristics because most are determined by several genes working together, with each making only a small contribution to the overall quality. It is often easier to determine where the quality genes, called quantitative trait loci, or QTL, are located on the barley chromosomes. By then selecting plants containing some easily measured gene that is located adjacent to, and on the same chromosome as, the QTL of interest, most of the selected plants will contain both the selected gene and the QTL of interest. This method is called "marker assisted selection." This paper reports how this method has been used to identify and characterize two areas of the barley genetic material that play major parts in controlling four aspects of malting quality. Of 90 barleys prepared by crossing a good malting barley with a poor one, the great majority of the best had inherited nearly all of their QTLs from the good malting quality parent. In a few cases, however, some of the genetic material was from the poor malting parent. This shows that breeders can use marker assisted selection to speed up the production of improved malting barleys but that they must use additional selection techniques to ensure that they keep only the highest quality barleys.
Technical Abstract: Identification of the quantitative trait loci (QTL) on barley chromosomes will help breeders select for improved quantitative traits by using linked molecular markers. Generally, three to ten loci affect each quantitative trait, with one or two having relatively large effects. The major loci need to be linked to molecular markers so that breeders can use them. QTL for malt extract (ME), alpha-amylase (AA), diastatic power (DP) and malt beta-glucan (MBG) have been mapped. Two QTL, located on chromosomes 1 and 4, strongly affect these traits. This study determined the associations between marker alleles and phenotypes at these major QTL regions. The two regions showed additive effects for all four traits, with Morex contributing all favorable alleles. A study of the flanking marker alleles of the best Morex x Steptoe lines showed that the QTL on chromosome 1 had more effect on ME and DP than that on chromosome 4. For AA and MBG, both alleles were equally effective. Five of the 9 top malting lines contained only Morex alleles, but some lines containing only Morex alleles did not have high malting quality. This indicates that malting quality depends not only upon major QTL alleles, but also upon contributions from some minor alleles. From this, it appears that breeders should first select lines on the basis of molecular markers and then reselect on the basis of phenotypic properties.