Submitted to: Proceedings International Barley Genetics Symposium
Publication Type: Proceedings
Publication Acceptance Date: 10/20/2000
Publication Date: N/A
Interpretive Summary: This paper reviews several aspects of our knowledge about the biochemistry of malting quality and about how genetic studies can be used to change that biochemistry to produce improved malting barley varieties. Many of the malting characteristics of a barley are determined by several different genes. Each gene contributes to a given property of the grain, but no single gene is strong enough to define the characteristic by itself. These are called 'quantitative' genes and their chromosome locations are called 'quantitative trait loci' or 'QTL'. In the past it has been almost impossible to determine exactly where the QTL were located on the barley chromosome, but researchers have recently reported the locations of 181 of these malting quality QTL. There are ways to select for the parts of the chromosomes that contain these QTL, and by selecting the ones that code for good quality and combining them in a single variety, better malting barleys can be produced. The QTL are sometimes located together with genes that control the synthesis of enzymes that would be expected to improve malting quality and sometimes they are not. In any case, we are now at the point where we can begin to successfully fuse our knowledge of the biochemistry, genetics and barley breeding to improve barleys. This knowledge will help barley researchers to more efficiently integrate their biochemistry and genetics studies and will allow breeders to more quickly and effectively develop improved malting barleys. This will help the malting and brewing industries by ensuring that they can obtain the improved barleys they need and will provide barley growers with improved varieties for which they can obtain acceptable prices.
Technical Abstract: This paper reviews several aspects of our knowledge about the malting quality of barleys and the biochemistry behind it, about the concept of quantitative trait loci (QTL) and about how QTL studies can be used to improve the malting quality of future barley cultivars. Most aspects of 'malting quality' are determined by the formation and activation of enzymes during malting, which in turn is controlled by the barley genetics. The really important quality determinants are the enzymes that degrade carbohydrates and proteins into small compounds that yeasts can metabolize during fermentation. This presumes, of course, that the plant's genetics allow it to perform well agronomically and that it does not show excessive dormancy that affects germination. Many of these individual biochemical and physiology characteristics are controlled by several different genetic loci, each of which controls only a portion of the effect. Together, these loci determine the usefulness of a cultivar for malting and brewing, but each contributes such a small part to determining the overall characteristic that it is often not measurable using standard genetic methods. These genetic loci are called QTLs. Recently, 181 malting quality QTLs have been reported and mapped on the barley genome. These are being used for genetic studies and for breeding improved barleys via marker assisted selection. In some cases the QTL are associated with genes that code for enzymes that reasonably should affect malting quality (i.e., extract QTL and beta-amylase genes) and in other cases they are not. We are finally at the point in malting quality research where we can begin to successfully integrate our knowledge of malting biochemistry with barley genetics and breeding.