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

66 BARLEY: GENETICS AND NUTRIENT COMPOSITION
concentrations along with linkages to genes controlling other components have
been identified. Aastrup (1983) and Molina-Cano et al. (1989) identified lowβ-glucan
mutant barleys that were attributed to a simple inheritance factor. Using
crossbreeding systems, Greenberg (1977) suggested that two or three dominant
genes are responsible for β-glucan levels. An additive genetic system of three
to five effective factors that control β-glucan content in barley was described by
Powell et al. (1989), but the chromosome location was not known. More recently,
Han et al. (1995) reported three QTLs located on chromosome 2(2H) and one
QTL located on chromosome 5(1H) that accounted for 34% of the total β-glucan
in a Steptoe/Morex mapping population.
It has been pointed out that genetic factors are largely responsible for β-glucan
levels in barley, but levels are also influenced by environmental growing conditions.
MacGregor and Fincher (1993) reported that β-glucan contents of barley
grain range from 2.0 to 11.0%, but usually fall between 4.0 and 7.0%. Changing
the amylose to amylopectin ratio in barley starch, with either the wax gene or the
amo1 gene, has a significant effect on increasing β-glucan content. Perhaps the
first report of increased levels of β-glucan in waxy barley was that of Ullrich et
al. (1986). Xue et al. (1997) reported increased β-glucan levels in waxy hulless
and covered isolines of Compana and Betzes barleys; 6.1 versus 4.85% (n = 18
per mean) in waxy and nonwaxy types, respectively. Ajithkumar et al. (2005)
reported a range from 5.6 to 5.75% β-glucans in four waxy lines developed at
Svalöf Weibull AB (Svalöv, Sweden) compared to 4.7% in a nonwaxy barley
cv. Golf. In a review, Fastnaught (2001) presented data from 16 separate studies
showing that β-glucan levels were increased by 32 to 41% in waxy barley compared
to nonwaxy barley. Much higher levels of β-glucans have been reported
in two unrelated waxy hulless barleys. Azhul is a six-rowed cultivar that most
consistently contains the highest levels of β-glucans (10 to 11%) in an otherwise
normal barley (Bengtsson et al. 1990; Bhatty 1992; Danielson et al. 1996).
Prowashonupana, a chemically induced mutant barley (Eslick 1979, 1981), contains
higher levels (15 to 16%) of β-glucans (Hofer 1985), but this is due in part
to a shrunken endosperm characteristic.
Similar increases of β-glucans were reported in high-amylose cultivars (Xue
1992; Swanston et al. 1997; Ajithkumar et al. 2005), although the numbers of
observations were not as large as that with the waxy types. According to Ullrich
(2002), the waxy and high-amylose genes interact with each other when the
two traits are introduced into the same genotype. Accordingly, the β-glucan and
starch levels are increased and decreased, respectively, exceeding simple additive
effects. Stahl et al. (1996) concluded that the association of high levels of β-glucan
with the waxy gene could not be broken. Fastnaught (2001) suggested that in
waxy cultivars, the genetic blockage of amylose production resulted in glucose
that is normally shunted to the starch biosynthetic pathway to be taken up by
the β-glucan biosynthetic pathway. In addition to causing an increase in the level
in waxy barley, the β-glucan molecular structure is also changed in that there is
a higher ratio of β-(1,3)-linked cellotriosyl units to β-(1,3)-linked cellotetraosyl
units (Jiang and Vasanthan 2000; Wood et al. 2003).