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

IMPROVING THE BARLEY CROP 37
Mutations
When used in connection with plant breeding, the term mutant or mutation has
a hazardous and even an intimidating connotation that often causes unwarranted
concern. Mutant barley plants occur spontaneously (naturally) as a result of errors
in normal cell processes (e.g., DNA replication), may be induced by a number of
chemical or radiation treatments, or may occur following cell and tissue culture
propagation. Mutagenesis research has been reported and reviewed extensively
in the scientific literature (Hockett and Nilan 1985). Regardless of the mutations
source, mutant barleys should not be considered as dangerous or undesirable. In
effect, natural and induced mutations have been a mainstay in producing genetic
variation since the advent of green plants; without genetic variation, improvement
of a species would not be possible.
Mutant barley may be utilized directly, providing an “instant” cultivar, but
more often, potentially useful mutations (especially when induced via chemicals
or radiation) are accompanied by other mutations, which must be removed
by an appropriate breeding method such as backcrossing. Both spontaneous and
mutant variants may provide evidence of genes at previously unknown loci as
well as new alleles in improved adapted genetic backgrounds, thus supplementing
and complementing a conventional breeding program. Mutagenesis has been
used extensively for development of new and improved cultivars and has provided
new methods of analyzing genetic fine structure and understanding genetic
control (Hockett and Nilan 1985). A relatively recent development in mutation
strategy enables a directed approach to identifying mutations in specific genes.
This procedure is described as targeting induced local lesions in genomes (TILL-
ING). Using this strategy, single-base-pair changes can be identified in a specific
gene of interest (McCallum et al. 2000; Till et al. 2003). Slade et al. (2005) identified
a range of waxy phenotypes in the wheat TILLING population, suggesting
that similar starch variants may be identified in barley. Using the TILLING technique,
point mutations and deletions in the powdery mildew resistant genes in
barley, mlo and mla, have been identified (Mejlhede et al. 2006), presenting an
opportunity to study resistance to these parasitic fungi.
A mutant barley resistant to powdery mildew was produced over 60 years ago
by Freisleben and Lein (1942) (cited by Ganeshan et al. 2008). As of 2007 there
were 256 various mutant barley varieties listed in the FAO/IAEA Mutant Varieties
database (FAO 2007). A number of mutant barleys have been identified with
genotypes expressing useful genetic characters—with important implications for
the food and brewing industries. The genetic background in the spontaneous
high-amylose starch mutant found in Glacier by Merritt (1967) may prove to be
invaluable in developing high-amylose starch barleys for use in specialty foods.
Induced mutants are also sources of valuable traits, such as increased kernel protein
(Doll 1973), high lysine (Jensen 1979), proanthocyanidin-free (Jende-Strid
1976), high β-glucan (Eslick 1981), low β-glucan (Aastrup et al. 1983), and
high-amylose starch (Merritt 1967; Morrell et al. 2003). The high-β-glucan barley
(Prowashonupana) produced by Eslick (1981) is an example of an instant
cultivar, as it is now being grown commercially without further modification.