Canada
January 26, 2007
Source: Canadian Food
Inspection Agency
Document DD2007-64
Determination of the safety of
BASF's
imidazolinone-tolerant CLEARFIELD™ durum wheat events DW2, DW6,
and DW12
This Decision Document has been
prepared to explain the regulatory decision reached under
Directive 94-08 (Dir94-08), entitled "Assessment Criteria
for Determining Environmental Safety of Plants with Novel
Traits", its companion biology document Bio2006-07, The
Biology of Triticum turgidum
ssp. durum
(Durum Wheat), and Directive 95-03 (Dir95-03), entitled
"Guidelines for the Assessment of Novel Feeds: Plant
Sources".
The Canadian Food Inspection
Agency (CFIA), specifically the Biotechnology Environmental
Release Assessment Unit (BERA) of the Science Strategies
Directorate and the Feed Section of the Animal Health and
Production Division have evaluated information submitted by
BASF.
This information is in regard to the imidazolinone tolerant
durum wheat events DW2, DW6, and DW12 (please note that DW2 and
DW6 are not considered novel feeds, as explained in Section
V). The
CFIA
has determined that these plants with a novel trait (PNT) do not
present altered environmental risk nor, as a novel feed, does
event DW12 present livestock feed safety concerns when compared
to currently commercialized durum wheat varieties in Canada.
Taking into account
these evaluations, unconfined release into the environment of
the CLEARFIELD™ durum wheat events DW2, DW6, and DW12 and use as
livestock feed of durum wheat event DW12 are authorized by the
Plant Biosafety Office (PBO) of the Plant Products Directorate
and the Feed Section of the Animal Health and Production
Division as of January 4, 2007. Any wheat lines derived from
events DW2, DW6, and DW12 may also be released into the
environment and any wheat lines derived from event DW12 may be
used as livestock feed, provided (i) no
inter-specific crosses are performed, (ii)
the intended uses are similar, (iii) it
is known, following thorough characterization, that these plants
do not display any additional novel traits and are substantially
equivalent to currently grown durum wheat, in terms of their
potential environmental impact and livestock feed safety.
Durum wheat events DW2,
DW6, and DW12 are subject to the same phytosanitary import
requirements as their unmodified counterpart.
Please note that the assessment
of livestock feed safety and environmental safety are critical
steps in the potential commercialization of these plant types.
Other requirements, such as the evaluation of food safety by
Health Canada, have been addressed separately from this review.
Table of Contents
I.
Brief Identification of the Modified Plant
II.
Background Information
III. Description and Assessment of the Novel Trait
- Development Method
- Imidazolinone Tolerance
- Stable Expression
IV.
Criteria for the Environmental Assessment
- Potential of events DW2,
DW6, and DW12 to Become Weeds of Agriculture or Invasive of
Natural Habitats
- Potential for Gene Flow
from events DW2, DW6, and DW12 to Wild Relatives Whose
Offspring May Become More Weedy or More Invasive
- Altered Plant Pest
Potential of events DW2, DW6, and DW12
- Potential Impact on
Non-Target Organisms of events DW2, DW6, and DW12
- Potential Impact on
Biodiversity of events DW2, DW6, and DW12
V.
Nutritional Criteria Assessment as Livestock Feed
- Potential Impact of event
DW12 on Livestock Nutrition
- Potential Impact of event
DW12 on Livestock and Workers/By-standers
VI.
New Information Requirements
VII. Regulatory Decision
|
Designation(s) of the Modified Plant: |
CLEARFIELD™
wheat events DW2, DW6, and DW12 (please note that events
DW2 and DW6 are not considered to be novel feeds, as
explained in Section V)
|
| Applicant: |
BASF Canada |
| Plant
Species: |
Durum Wheat
(Triticum turgidum
spp.
durum L.) |
| Novel
Traits: |
Tolerance
to imidazolinone herbicides |
| Trait
Introduction Method: |
Chemically
induced seed mutagenesis |
| Proposed
Use of the Modified Plant: |
Production
of wheat for livestock feed and human food |
BASF
has developed durum wheat events tolerant to imidazolinone
herbicides. These wheat events were developed to provide an
alternative strategy for weed control.
The development of the
CLEARFIELD™ durum wheat events DW2, DW6, and DW12 was
accomplished using chemically induced seed mutagenesis. The DW2,
DW6, and DW12 events are allotetraploid (28 chromosomes n=14),
belonging to genus and species Triticum
turgidum spp.
durum L.
Durum wheat carries two complete genomes designated ‘A' and ‘B'.
Each genome has an
AHAS gene (ALS3
and ALS2,
respectively). The herbicide tolerance in events DW2, DW6, and
DW12 results from a single point mutation modification in the
ALS3
acetohydroxyacid synthase (AHAS) gene in the durum wheat genome
such that the resulting modified enzyme has a single amino acid
substitution and is no longer affected by imidazolinone
herbicides.
BASF
has provided data on the identity of the durum wheat events, a
detailed description of the modification method and breeding
history, information on the modified gene, the resulting protein
and its mode of action and the stability of trait expression.
Durum wheat event DW12 was
field tested in the United States in 2003 and 2004. Events DW2
and DW6 were field tested in Canada in 1998, 1999, 2000, 2001,
2004, and 2005. Agronomic characteristics of events DW2, DW6,
and DW12 such as seed germination, seedling emergence, seeding
vigor, foliar disease susceptibility, insect damage, plant
height, days to heading, days to maturity, harvest moisture,
test weight and grain yield were compared to those of unmodified
wheat counterparts.
Nutritional components of durum
wheat event DW12 such as proximates, amino acids and fatty acids
were compared with unmodified wheat counterparts.
Anti-nutritional factors were also determined.
BASF
has provided an agronomic stewardship plan for imidazolinone
tolerant durum wheat in the Canadian environment. This plan
includes information regarding a safe and sustainable deployment
of imidazolinone-tolerant durum wheat and an efficient mechanism
for growers to report agronomic problems with this product to
BASF.
The Biotechnology Environmental
Release Assessment Unit (BERA) of the Science Strategies
Directorate,
CFIA, have reviewed the above information, in light of
the assessment criteria for determining environmental safety of
PNTs, as
described in the Directive 94-08 (Dir94-08), entitled
"Assessment Criteria for Determining Environmental Safety of
Plants With Novel Traits".
BERA has considered the:
- potential of events DW2,
DW6, and DW12 to become weeds of agriculture or be invasive
of natural habitats;
- potential for gene flow
from events DW2, DW6, and DW12 to wild relatives whose
hybrid offspring may become more weedy or more invasive;
- potential of events DW2,
DW6, and DW12 to become a plant pest;
- potential impact of events
DW2, DW6, and DW12 or their gene products on non-target
species, including humans; and
- potential impact of events
DW2, DW6, and DW12 on biodiversity.
The Feed Section of the Animal
Health and Production Division,
CFIA,
has also reviewed the above information pertaining to durum
wheat event DW12 with respect to the assessment criteria for
determining the safety and efficacy of livestock feed, as
described in Directive 95-03 (Dir95-03), entitled "Guidelines
for the Assessment of Novel Feeds: Plant Sources" (please note
that events DW2 and DW6 are not considered to be novel feeds, as
explained in Section V). The Feed Section
has considered:
- potential impact of event
DW12 on livestock nutrition; and
- potential impact of event
DW12 on livestock and workers/by-standers.
| 1.
Development Method |
| |
The original mutant
durum wheat events DW2, DW6, and DW12 were isolated from
populations derived by chemical-induced mutagenesis with
ethyl methanesulfonate (EMS) and sodium azide of wheat
seed. Whole plant selection procedures for herbicide
tolerance were used (seedlings were sprayed with
imidazolinone herbicides; only tolerant plants lived and
were used in the following breeding generations). |
| 2.
Imidazolinone Tolerance |
| |
Imidazolinone
herbicides are active against the enzyme
acetohydroxyacid synthase (AHAS), also known as
acetolactate synthase (ALS).
AHAS
is an enzyme found in bacteria, certain other
micro-organisms and plants. This enzyme catalyses the
first step in the biosynthesis of the essential branched
chain amino acids isoleucine, leucine and valine.
Herbicide-induced
AHAS
inhibition results in a lethal decrease in protein
synthesis. Unmodified wheat is not tolerant to
imidazolinone herbicides.
A single amino acid
substitution in the
AHAS
enzyme was sufficient to alter the binding site for
imidazolinone herbicides, resulting in the tolerant
phenotype.
The novel imidazolinone
tolerance is under the control of the native
AHAS
promoter and is believed to be constitutively expressed.
Sequence information for the modified
AHAS
gene in durum wheat events DW2, DW6, and DW12 was
submitted.
The tolerance to
imidazolinone was demonstrated by comparison of the
activity of the
AHAS
enzyme extracted from durum wheat events DW2, DW6, and
DW12 to that of conventional durum wheat plants. In the
absence of the herbicide, the
AHAS
enzyme activity was similar, but when imidazolinone
herbicide was added to the assay, the enzyme activity of
the susceptible plants was inhibited much more than
enzyme from the tolerant plants.
The levels of valine,
leucine and isoleucine produced in wheat are regulated
by feedback inhibition of
AHAS.
BASF provided data to demonstrate that the
modified AHAS
shows similar feedback inhibition by valine and leucine
as compared to unmodified
AHAS.
The modification of the
AHAS
does not affect feedback inhibition and hence, the
regulation and levels of these amino acids.
The amino acid sequence
of mutated
AHAS differs by one amino acid from that of
unmodified durum wheat. Unlike known food allergens,
AHAS
is a minor protein in plant tissue, it is heat sensitive
and trypsin susceptible. The
AHAS
protein from durum wheat events DW2, DW6, and DW12 was
shown to be heat sensitive, with no detectable activity
of AHAS
after 1 minute of heating at 100°C
AHAS
from events DW2, DW6, and DW12 were shown to be
equivalent to parental controls with respect to trypsin
degradation. The unmodified form of the
AHAS
protein shows no amino acid similarity to known
allergens.
BASF provided evidence to show that the
protein components of durum wheat events DW2, DW6, and
DW12 are not altered in comparison with an unmodified
comparator.
HPLC was performed on protein extracts from
unmodified and modified durum wheat and indicated that
no new major proteins or increased protein expression
occurred as a result of the mutagenic event.
BASF has provided a method for the detection
and identification of durum wheat containing this novel
trait to the
CFIA. |
| 3.
Stable Expression |
| |
Selections for durum
wheat events DW6 and DW2 were made based on
imidazolinone tolerance across at least 11 and 27
generations, respectively. Additionally, the segregation
of herbicide tolerance in events DW2 and DW6 was
consistent with the inheritance of a single gene. Durum
wheat event DW12 demonstrated consistent herbicide
tolerance over multiple breeding generations, confirming
the stable inheritance of this trait. |
| 1.
Potential of events DW2, DW6, and DW12 to Become Weeds
of Agriculture or Invasive of Natural Habitats |
| |
Durum wheat possesses
few of the characteristics that are common to weeds and
invasive plants. It is an annual crop that does not
persist in unmanaged ecosystems without human
intervention. Durum plants can grow as volunteers in
cultivated fields in the seasons following a durum crop,
but they are usually eliminated by soil cultivation or
the use of herbicides. There have been no reports of
durum wheat becoming an unmanageable weed of agriculture
or an invasive pest, in North America or the world.
The
CFIA
evaluated data submitted by
BASF on the biology of durum wheat events DW2,
DW6, and DW12, and determined that vegetative vigour,
time to maturity, seed production (yield), lodging
resistance, and resistance to insects and disease were
within the normal range of expression of these traits
currently displayed by the parent variety.
No competitive
advantage was conferred on plants with durum wheat
events DW2, DW6, or DW12, other than that conferred by
tolerance to imidazolinone herbicides, as none of the
reproductive or growth characteristics of these events
were different from those of the parent variety.
Tolerance to imidazolinone herbicides provides a
competitive advantage only when these herbicides are
used, and will not, in and of itself, make a plant
weedier or more invasive of natural habitats.
Imidazolinone tolerance will not cause plants with
events DW2, DW6, or DW12 to become weedier or more
invasive in managed habitats than unmodified
T. turgidum
spp. durum.
Imidazolinone-tolerant durum volunteers will not be
controlled in subsequent crops if imidazolinone is used
as the only weed control tool. However, control of
imidazolinone-tolerant durum as a volunteer weed in
other crops or in fallow ground can readily be achieved
by the use of classes of herbicides other than
imidazolinones, or by mechanical means.
The novel trait has no
intended or observed effects on weediness or
invasiveness. The
CFIA
has therefore concluded that these durum events have no
altered weed or invasiveness potential in Canada when
compared to conventional durum varieties.
The agronomic
stewardship plan, which contains a herbicide tolerance
management plan, submitted by
BASF was evaluated by the
CFIA
and determined to be satisfactory. This stewardship plan
applies to the durum wheat events described in this
document as well as durum wheat event DW1 (see Decision
Document DD2006-63) and bread wheat events BW255-2 and
BW238-3 (see Decision Document DD2006-60). The herbicide
tolerant stewardship plan includes recommendations on
agricultural practices concerning imidazolinone tolerant
durum and provides an efficient mechanism for growers to
report agronomic problems with this product to
BASF, which will facilitate the ongoing
monitoring of imidazolinone tolerant durum. In addition,
BASF is required to monitor grower compliance
to determine the effectiveness of the stewardship plan
and make any changes to the plan as appropriate.
In the longer term,
widespread adoption of several different crop species
with specific associated weed management systems (i.e.
numerous crop species each with one or more tolerances
to different herbicides) may lead to the development of
crop volunteers with a combination of novel tolerances
to different herbicides. This could result in the loss
of the use of these herbicides and any of their
potential benefits. Therefore,
BASF will make their stewardship plan readily
available to growers and agriculture extension
personnel, in both private and public sectors, to
promote careful management practices for durum wheat
events DW2, DW6, and DW12. These practices include the
use of alternate control tools as appropriate to achieve
complete weed and volunteer control (which is also
recommended to help minimize the development of
resistant weed populations). |
| 2.
Potential for Gene Flow from events DW2, DW6, and DW12
to Wild Relatives Whose Offspring May Become More Weedy
or More Invasive |
| |
No known wild
Triticum species exist
in North America. The closest known relatives in North
America are members of the Aegilops
genus. Aegilops cylindrica,
jointed goat grass, is present in the United States
where it can be found as a weed in winter wheat fields,
but is not reported in Canada (nor are any other
Aegilops species).
Additionally, Aegilops cylindrica
does not readily produce fertile progeny when hybridized
with durum (research studies indicate that
Aegilops cylindrica x durum hybrids are sterile).
A. cylindrica
is included in the provincial Noxious Weed List in
British Columbia to prevent and/or delay the spread of
this weed into Canada.
The only weed species
found in Canada that is closely related to durum is
Agropyron repens (quackgrass).
A. repens is a
common and troublesome weedy grass of agricultural areas
throughout Canada. However, no known naturally-occurring
hybrids between durum and Agropyron species
have been reported, and published literature on the
genetics of Triticum and Agropyron
indicate that natural crossing between these two genera
is unlikely.
Triticale is a crop
that has been developed by humans by crossing wheat (Triticum
aestivum or T.
turgidum) with rye (Secale cereale). There
have been no reports of triticale serving as a
hybridization bridge between wheat and rye.
The
CFIA
has therefore determined that gene flow from durum wheat
events DW2, DW6, and DW12 to wild or weedy species in
Canada is very unlikely. |
| 3.
Altered Plant Pest Potential of events DW2, DW6, and
DW12 |
| |
The intended effect of
the novel trait is unrelated to plant pest potential.
T.
turgidum is not a plant pest in Canada.
Additionally, the agronomic characteristics of durum
events DW2, DW6, and DW12 (including the responses to
insect and disease pressures) were shown to be within
the normal range of conventional durum varieties.
The
CFIA
has therefore determined that durum events DW2, DW6, and
DW12 do not present a plant pest concern. |
| 4.
Potential Impact on Non-Target Organisms of events DW2,
DW6, and DW12 |
| |
A single amino acid
modification of the
AHAS
enzyme, which alters the herbicide binding site on the
enzyme, is the molecular basis for imidazolinone
tolerance in durum wheat events DW2, DW6, and DW12.
BASF has submitted data indicating that the
modified AHAS
is substantially equivalent to its unmodified
counterparts with respect to enzyme activity
(biosynthesis of the precursor molecule of valine,
leucine, and isoleucine) and feedback inhibition (from
valine and leucine). The modified
AHAS
enzyme only differs from the unmodified enzyme by being
less inhibited by imidazolinone herbicides. The mutant
AHAS
in events DW2, DW6, and DW12 has not significantly
affected the biosynthesis of the branched- chain amino
acids, valine, leucine and isoleucine. The detailed
compositional analysis has led to the conclusion that
durum wheat events DW2, DW6, and DW12 are substantially
equivalent to their parent variety.
The
AHAS
enzyme is not a known toxin, does not confer resistance
to agricultural pests and is commonly found in a wide
variety of plants and micro-organisms with a history of
safe use. No novel toxins were introduced into this
variety. Therefore, no negative interactions with
non-target symbiotic or consumer organisms are
anticipated.
In addition, agronomic
characteristics, pathogen interactions, and insect pest
susceptibility of durum wheat events DW2, DW6, and DW12
are within the range of expected values displayed by
currently commercialized durum varieties. The
CFIA
concluded that there were not likely to be significant
unintended changes to durum wheat events DW2, DW6, and
DW12 that could have adverse impacts on non target
organisms. |
| 5.
Potential Impact on Biodiversity of events DW2, DW6, and
DW12 |
| |
Durum wheat events
DW2, DW6, and DW12 are safe to non-target organisms, do
not present altered weediness or plant pest potential
and are not intended to be grown in Canada. In addition
the novel trait has not altered the ability of this line
to persist in the Canadian environment.
The
CFIA
has therefore concluded that the potential impact on
biodiversity of durum wheat events DW2, DW6, and DW12 is
equivalent to that of currently commercialized durum
lines. |
|
Note: Based on information provided by
BASF, the imidazolinone-tolerance trait
observed in durum wheat events DW2 and DW6 is the result
of a genetic modification that is equivalent to the
genetic modification leading to the
imidazolinone-tolerance trait observed in durum wheat
event DW12, and durum wheat events DW2 and DW6 are
substantially equivalent to event DW12 in terms of
livestock feed safety. Therefore, with the authorization
of event DW12, events DW2 and DW6 are no longer novel
livestock feeds. |
| 1.
Potential Impact of event DW12 on Livestock Nutrition |
| |
Nutritional
Composition and Anti-Nutritional Factors
Nutritional composition
data was obtained from durum wheat event DW12 and the
parental variety, which were grown in the United States
in 2003 and 2004. Grain samples were analyzed for
protein, fat, fibre,
ADF,
TDF,
amino acids, fatty acids, minerals and vitamins. There
were no statistically significant differences between
event DW12 and the control for protein, fat,
ADF,
TDF,
branched chain amino-acids and essential amino acids for
both years. Crude fibre in event DW12 was significantly
higher than parent control in the 2003 study but
comparable to conventional durum wheat varieties. Fatty
acids measured in event DW12 were statistically
significantly different from the control in the 2003
study. All fatty acids were within the range of
conventional durum wheat varieties. Potassium was
significantly higher in event DW12 compared to the
control in 2003. Vitamin B1 and folic acid were
significantly different in event DW12 compared to the
control in the 2003 study. However vitamin and mineral
levels were within ranges of commercial durum wheat
varieties for both years.
Phytic and trypsin
inhibitor were analyzed in durum wheat event DW12 and
compared to the parental variety. There were no
statistically significant differences in phytic acid
between event DW12 and the parental variety for both
years. Trypsin inhibitor was not detected in event DW12
or the parental control.
The evidence provided
by
BASF supports the conclusion that the
nutritional composition of durum wheat event DW12 is
equivalent to conventional durum wheat varieties.
|
| 2.
Potential Impact of event DW12 on Livestock and
Workers/By-standers |
| |
The
AHAS
enzyme is found in a wide variety of plants and
micro-organisms.
AHAS
is not a known toxin or allergen and a single base pair
change would not be expected to change this.
AHAS
from durum wheat event DW12 is feedback inhibited as is
unmodified
AHAS, it is present in small amounts in the
feed, it is heat labile and it is rapidly degraded under
conditions in the gastrointestinal tract. The expression
of AHAS
is not changed by the modification. Based on the
information provided by
BASF, the modified
AHAS
is unlikely to be a novel toxin or allergen.
Based on the detailed
characterization provided (nutritional composition,
agronomic data and
HPLC protein profiles of the modified plant
compared to the unmodified comparator) it is unlikely
that secondary mutations causing unintended effects have
occurred in the durum wheat genome.
The evidence provided
by
BASF supports the conclusion that the
potential impact on livestock and workers/by-standers of
durum wheat event DW1 is equivalent to that of currently
commercialized durum lines. |
If at any time,
BASF
becomes aware of any information regarding risk to the
environment, including risk to human or animal health, that
could result from release, in Canada or elsewhere, of durum
wheat events DW2, DW6, and DW12, their descendants, or products
derived there from,
BASF
must immediately provide such information to the
CFIA.
On the basis of such new information, the
CFIA
will re-evaluate the potential impact of events DW2, DW6, and
DW12 on the environment, livestock and human health, and may
re-evaluate its decision with respect to the livestock feed use
and environmental release authorizations of events DW2, DW6, and
DW12.
Based on the review of data and
information and stewardship plan, submitted by
BASF,
and through comparisons of durum wheat events DW2, DW6, and DW12
with unmodified durum wheat counterparts, the Biotechnology
Environmental Release Assessment Unit,
CFIA,
has concluded that the modified gene and its corresponding trait
do not confer to durum wheat events DW2, DW6, and DW12 any
characteristic that would result in intended or unintended
significant environmental effects following unconfined release.
Based on the review of data and
information submitted by
BASF,
including comparisons of durum wheat event DW12 with unmodified
durum wheat counterparts, the Feed Section,
CFIA,
has concluded that the modified gene and its corresponding novel
trait will not confer to these plants any characteristic that
would raise any concerns regarding the safety or nutritional
composition of durum wheat event DW12. Wheat grain, its
byproducts and wheat germ oil, are currently listed in Schedule
IV of the Feeds Regulations and
are, therefore, approved for use in livestock feeds in Canada.
Durum wheat event DW12 has been assessed and found to be as safe
and nutritious as traditional durum wheat varieties. Durum wheat
event DW12 and its products are considered to meet the present
ingredient definitions and are approved for use as livestock
feed ingredients in Canada.
Taking into account
these evaluations, unconfined release into the environment of
the CLEARFIELD™ durum wheat events DW2, DW6, and DW12 and use as
livestock feed of durum wheat event DW12 are authorized by the
Plant Biosafety Office of the Plant Products Directorate and the
Feed Section of the Animal Health and Production Division as of
January 4, 2007. Any wheat lines derived from events DW2, DW6,
and DW12 may also be released into the environment and any wheat
lines derived from event DW12 may be used as livestock feed,
provided no inter-specific crosses are performed, provided the
intended uses are similar, and provided it is known, following
thorough characterization, that these plants do not display any
additional novel traits and are substantially equivalent to
currently grown durum wheat, in terms of their potential
environmental impact and livestock feed safety.
The CLEARFIELD™ durum
wheat events are subject to the same phytosanitary import
requirements as its unmodified counterparts.
Please refer to
Health Canada's Decisions on Novel Foods for a description
of the food safety assessment of CLEARFIELD™ durum wheat events.
The food safety decisions are available at the following Health
Canada web site:
http://www.hc-sc.gc.ca/fn-an/gmf-agm/index_e.html
This bulletin is published by
the Canadian Food Inspection Agency. For further information,
please contact the Feed Section or Plant Biosafety Office at:
Feed
Section
Animal Health and Production Division
Animal Products Directorate
59 Camelot Drive
Ottawa, Ontario K1A 0Y9
Telephone: 613-225-2342
Facsimile: 613-228-6614 |
Plant
Biosafety Office
Plant Products Directorate
59 Camelot Drive
Ottawa, Ontario K1A 0Y9
Telephone: 613-225-2342
Facsimile: 613-225-6140 |
|
