Barley for Food and Health: Science, Technology, and Products

GENETICS AND NUTRIENT COMPOSITION 57
genetics and by environmental growing conditions, including farming practices
such as irrigation and genetic–environment interaction. By using superior
germplasm and controlling certain environmental factors such as moisture available
through irrigation, a reasonably uniform barley crop can be produced from
one growing season to the next. In this chapter we provide a brief introduction
to the genetics of barley, the application of genetics in breeding barley for food,
and the chemical components or nutrients of the barley kernel relative to their
location in the kernel.
GENETICS AND NUTRIENT COMPOSITION
To date, a great amount of scientific information on the barley genome has been
generated. This is partially due to the international importance of barley as a
major crop but also to the dedication of scientists who have a genuine interest
in studying this fascinating grain. The genetics of barley has probably been
explored to a greater extent than that of any other cereal grain. According to
Hockett and Nilan (1985), cultivated and wild barleys are major experimental
organisms among flowering plants for genetic studies. The wide use of barley in
genetic studies was attributed to (1) its diploid nature, (2) its low chromosome
number (2n = 14), (3) the relatively large chromosomes (6 to 8 μm), (4) the
high degree of self-fertility, and (5) the ease of hybridization. The reader is
referred to the following for discussion of barley genetics in greater depth than is
presented in this book: Smith 1951; Nilan 1964, 1974; Hockett and Nilan 1985;
Wettstein-Knowels 1992; Nilan and Ullrich 1993; Barley Genetics Newsletter
1996; Kleinhofs and Han 2002; and Ullrich 2002.
The barley genome contains a vast number of genes that determine food quality
traits, many of which have not yet been characterized. Some traits are unique
to barley, but most are shared with other cereal grain species. There are several
anatomical traits that are controlled by one or two genes (simply inherited),
but most traits involving complex physiological processes are inherited quantitatively,
being controlled by several to many genes. Genetic knowledge of many
simply inherited traits dates back many years, whereas reliable data about the
inheritance of the quantitative traits have been limited until relatively recently
with the development of comprehensive molecular marker–based genetic maps
and the technology of quantitative trait locus (QTL) analysis (Ullrich 2002). The
importance of this technology was summed up by Nilan (1990): “The comprehensive
molecular marker linkage maps have proved a powerful tool in barley for
identifying QTL loci for agronomic and quality traits, determining QTL effects
and action, and facilitating genetic engineering.”
In discussing genetically controlled traits in a biological system such as barley,
it is customary to identify the genes(s) and the location on the chromosome
involved when this information is known. Barley has seven pairs of chromosomes
that have been defined based on their sizes and characteristics (Nilan
1964; Ramage 1985). Chromosomes 1 through 5 differ in their sizes measured