Transgenic Applications in Wheat Improvement - Wheat Science and Trade - page 402

tional genetic traits. Rakszegi et al. (2005) grew
one transgenic line from this set and its parent
in an arid continental climate for 3 years. The
transgenic and control lines had the same grain
yields; expression of the 1Dx5 transgene
remained at high levels, four times that of native
HMW-GS genes.
Bregitzer et al. (2006) compared the fi eld per-
formance of 50 transgenic wheat lines with altered
HMW-GS composition versus four lines with
only the Ubi1::bar selection gene, 10 non-
transgenic sister lines (null segregants), and the
nontransformed parent across multiple years and
locations. The null segregants and the lines con-
taining only the selection gene did not differ in
yield or heading date from the nontransformed
control. The HMW-GS transgenic group had
lower mean grain yield than the nontransformed
control group, but most of the difference was
attributable to decreased yields of seven individ-
ual lines at all locations. The majority of the
transgenic lines were indistinguishable in agro-
nomic performance from their non-transgenic
sibs and parent. Expression of the HMW-GS
transgenes was the same between years. The
authors concluded that changes in HMW-GS
composition can be made by genetic transforma-
tion without necessarily altering wheat growth,
development, or seed characteristics.
Among the more than 3,000 wheat plants
directly selected for transgene-encoded glypho-
sate resistance (Hu et al., 2003), one was selected
by Monsanto Corporation as a candidate for
commercial release as Roundup Ready wheat.
This line contained a single insertion of a single
copy of a construct containing two EPSPS genes,
one under control of the rice Act1 promoter and
intron and the other under control of the 35 S
promoter and an intron from a maize heat shock
protein gene. In addition to its simple integration
structure, the criteria for selection of this line
included stable expression of the EPSPS enzyme
over nine generations, inheritance of resistance
as a stable dominant trait, survival of 1.68 kg
acid-equivalent per hectare spray application of
glyphosate, more than 80% fertility after 3.36 kg
acid-equivalent of glyphosate, and good agro-
nomic performance in fi eld trials at 13 or 14 loca-

tions over 3 years (Hu et al., 2003). In the fi eld,
this line showed no damage after application of
up to 4 L glyphosate per hectare. Yield and agro-
nomic traits of the transgenic line were indistin-
guishable from the nontransformed parent,
whether or not glyphosate was applied to the
transgenic plants (Zhou et al., 2003). Blackshaw
and Harker (2002) found a 4%-16% yield advan-
tage of the transgenic line when glyphosate was
used to control weeds compared with conven-
tional weed control measures. In addition, this
line had reduced dockage content (Wilson et al.,
2003).
Based on this line's performance and charac-
teristics, Monsanto Corporation petitioned the
US Animal and Plant Health Inspection Service
and the Food and Drug Administration for their
approvals for commercial release. As a result,
glyphosate-resistant wheat became the subject of
several other published investigations. It was
found to be equivalent to nontransformed wheat
in chicken feeding studies (Kan and Hartnell
2004). The results of a risk assessment for com-
mercial release of the transgenic glyphosate-
resistant wheat were published by Peterson and
Shama (2005), who concluded that it posed no
more risk to the environment, humans, livestock,
and wildlife than release of imidazdolone-
resistant wheat obtained by standard mutagene-
sis. Harvey et al. (2003) found no difference
between transgenic glyphosate-resistant wheat
and its non-transgenic parent for survival and
growth of greenbug [ Schizaphis graminum
(Rondani)], Russian wheat aphid [ Diuraphis noxia
(Mordvilko)], or wheat curl mite [ Aceria tosi-
chella (Keifer)], nor did they fi nd any difference
in survival of the transgenic and non-transgenic
lines after infestation with the insects or in trans-
mission of Wheat streak mosaic virus from curl
mite. Lupwayi et al. (2007) found no consistent
or large effects on soil microorganism communi-
ties when glyphosate-resistant wheat and canola
( Brassica napus L.) were rotated at six Canadian
prairie sites. Unexpectedly, sexually derived
advanced breeding lines carrying the resistance
transgene were found to be transiently resistant
to leaf rust and stem rust (latter caused by
Puccinia graminis Pers.:Pers. f. sp. tritici Eriks.