Agriculture Reference
In-Depth Information
rarely will be encountered with white wheat pro-
duced in the Great Plains, especially in sites west
of the 100th meridian. However, genetic diversity
exists among both red and white wheat for sprout-
ing tolerance (Wu and Carver 1999).
Rio Blanco is reported to be among the most
tolerant HW cultivars (Wu and Carver 1999); an
older HW cultivar, Clark's Cream, also has served
as a source of genes for preharvest sprouting tol-
erance (Morris and Paulsen 1992). Nuplains, a
recently released HW wheat cultivar, has toler-
ance similar to Rio Blanco.
Tolerance to preharvest sprouting may be
assessed by use of misting systems and determi-
nation of α-amylase activity; however, such
approaches can encounter unacceptably high
error frequencies with fi eld-grown materials.
Alternative approaches include germination
studies of seed harvested at physiological matu-
rity and rapidly dried (Wu and Carver 1999) or
germination of such seed in the presence of the
germination inhibitor, abscisic acid (ABA) (Morris
et al., 1989). Germination in lines susceptible to
preharvest sprouting will not be suppressed by
ABA. Gibberellic acid (GA3) stimulates germina-
tion and acts as an antagonist of ABA (Gold and
Duffus 1992).
Genetic studies on inheritance of preharvest
sprouting tolerance generally indicate polygenic
inheritance (Paterson and Sorrells 1990).
However, the number of North American popu-
lations studied is quite limited, and studies on
inheritance of the trait in more recent cultivars,
such as Rio Blanco and Nuplains, are lacking. It
is not known, for example, whether pyramiding
of tolerance genes from different sources will
result in genetic gains in improvement to sprout-
ing tolerance. Also, while the pigments or their
precursors present in red-grained cultivars confer
resistance to preharvest sprouting, genetic diver-
sity exists among red wheat genotypes for the
trait. Red-grained cultivars might serve as a
genetic reservoir for additional genes for toler-
ance to preharvest sprouting in white wheat.
Such an approach was successfully employed by
Hucl and Matus-Cadiz (2002) in the develop-
ment of white spring wheat with improved seed
dormancy.
Hard white wheat—consumer markets
The total supply of white wheat in the United
States has remained steady at 9.2 million tonnes
in 1989-1990 and 9.3 million tonnes in 2008-
2009, with a peak of 12.9 million tonnes in 1996-
1997 (Anonymous 2007). However, HW wheat
production peaked in 2003, refl ecting the 3-year
incentive program for HW wheat in the 2002
Farm Act for harvest years 2003-2005. The HW
harvest in those three seasons was 1.12 million
tonnes, 1.03 million tonnes, and 0.96 million
tonne, respectively. Kansas had more than one-
half of the US HW acreage in 2003 based on
incentive program enrollment data (Lin and
Vocke 2004). This was followed by a 0.68 million
tonne HW wheat harvest in 2006 (A. Harris, pers.
comm.). This loss of production volume after the
incentive program ended reinforced growers'
concerns about additional risks of preharvest
sprouting and handling costs associated with
growing and delivering HW wheat, and offered
no assurance of premiums over HRW wheat.
A major benefi t of HW wheat is that it allows
millers to achieve a higher milling yield, based on
fl our color—as much as 1%-3% more than HRW
wheat. Though fl our color is correlated with bran
content of fl our, higher milling yield and more
nutrition might be achieved in HW fl our without
an unfavorable change in color. This was con-
fi rmed in a study by McFall et al. (2003), who
conducted milling studies on a popular HRW cul-
tivar and two HW cultivars. They plotted cumu-
lative ash and Agtron whiteness values against
milling yield. Ash values surpassed 0.5% ash at
>
75% milling yield for all three HW cultivars.
The two HW cultivars produced 1.2%-2.3%
higher fl our yield, with Agtron whiteness values
of 5.9%-10.7 units higher than the HRW culti-
var. Agtron values showed that HW cultivars
achieved the same whiteness at 85%-90% milling
yield as the HRW cultivar showed at 40%. McFall
et al. (2003) concluded that compared with HRW
wheat, HW wheat could provide the same color
of fl our at higher milling yields, or that whole-
wheat fl our could be prepared from HW wheat
nearly as white as standard-grade fl our from
HRW wheat.
