Genetically modified maize pollen ...
Genetically modified maize pollen movement and crop coexistence, GMO
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Genetically modified maize:
pollen movement and crop co-
existence
By
Graham Brookes & Peter Barfoot (PG Economics Ltd, UK)
Enric Melé & Joaquima Messeguer (Institut de Recerca I
Tecnologia Agroalimentàries, Spain)
Florence Bénétrix, Daniel Bloc & Xavier Foueillassar (Arvalis,
France)
Adeline Fabié & Cedric Poeydomenge (Maiz Europ, France)
26 November 2004
GM maize – pollen movement and crop co-existence
Table of contents
1 Introduction ............................................................................................................................ 3
2 GM pollen and crop co-existence ........................................................................................... 3
2.1 What is co-existence? ...................................................................................................... 3
2.2 How can adventitious presence occur?............................................................................ 4
2.3 Adventitious presence in maize ....................................................................................... 4
2.3.1 Cross-pollination
...................................................................................................... 4
2.3.2 Seed mediated pollen flow (ie, volunteers)
............................................................... 5
2.3.3 Other possible sources of adventitious presence in maize
....................................... 5
3 Adventitious presence in maize from cross-pollination: review of literature and experience 6
3.1 General studies of pollen flow and cross-pollination in maize........................................ 6
3.2 Specific studies examining cross-pollination between GM and non GM maize crops in
Europe ................................................................................................................................... 9
3.2.1 Melé et al (2004)
...................................................................................................... 9
3.2.2 APROSE (2003/4)
....................................................................................................10
3.2.3 Bénétrix and Bloc (France) 2002 & 2003
...............................................................12
3.2.4 Henry et al (UK) 2003
.............................................................................................12
3.2.5 Summary of findings from cross pollination & co-existence studies between GM
and non GM maize
............................................................................................................13
3.3 Practical experience of co-existence and minimising levels of cross-pollination between
GM and non GM maize crops ..............................................................................................14
3.3.1North America
..........................................................................................................14
3.3.2 Spain
........................................................................................................................15
4 Conclusions ...........................................................................................................................16
Bibliography .............................................................................................................................19
©PG Economics 2004
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GM maize – pollen movement and crop co-existence
1 Introduction
Genetically modified (GM) maize was planted on a total of 15.5 million hectares in 2003
(11% of the global maize area). In the EU, GM maize
1
is the only GM crop currently grown
commercially. In Spain, the main location where the crop has been planted since 1998, it
accounted for about 7% of the total maize area in 2003 (31,000 hectares). Estimates for 2004
plantings are 60,000 hectares
2
.
Against this background, one of the main subjects of current debate about the use of GM
crops such as maize relates to the economic and market implications of GM and non GM
crops being grown in close proximity (ie, co-existing). Within this co-existence debate, it is
often claimed that GM and conventional (including organic) crops cannot co-exist without
causing significant economic harm/losses to conventional and organic growers.
This paper
3
examines these issues, with specific reference to maize and the extent to which
adventitious presence of GM maize may be detected in non GM maize crops through maize
pollen movement and gene flow.
The paper, after this introduction is structured as follows:
¾
Section 2: What is co-existence and the role of pollen movement and gene flow;
¾
Section 3: Adventitious presence arising from cross-pollination in maize: a review of
literature and experience;
¾
Section 4: Conclusions.
2 GM pollen and crop co-existence
2.1 What is co-existence?
Co-existence as an issue relates to ‘
the economic consequences of adventitious presence of
material from one crop in another and the principle that farmers should be able to cultivate
freely the agricultural crops they choose, be it GM crops, conventional or organic crops’
4
.
The issue is, therefore, not about product/crop safety
5
, but relates solely to the production and
marketing of crops approved for use.
Adventitious
6
presence of GM crops in non-GM crops becomes an issue where consumers
demand products that do not contain, or are not derived from GM crops.
The main legal requirement in the EU of relevance to the planting of GM maize is the
labelling requirements for products containing or derived from GMOs
7
. These set the
1
Insect resistant (Bt)
2
Source: Spanish maize growers association (AGPME)
3
The authors acknowledge that Agricultural Biotechnology in Europe (ABE) have given their support to the study.
The material presented in this paper is, however the independent views of the authors
4
Source: European Commission 2003
5
Commercially grown GM crops having obtained full regulatory approval for variety purity, use in livestock feed,
human health and safety for the environment. The issue of environmental liability (sometimes confused with
economic liability) is addressed through the regulatory approval process
6
Or sometimes referred to as technically unavoidable
7
Regulation EC 1829/2003 on GM food and feed
©PG Economics 2004
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GM maize – pollen movement and crop co-existence
adventitious presence threshold for positive labelling of food and feed products containing or
derived from GM crops at 0.9%.
2.2 How can adventitious presence occur?
Adventitious presence of unwanted material can arise for a variety of reasons. These include,
seed impurities, cross-pollination, volunteers (self sown plants derived from seed from a
previous crop), and may be linked to seed planting equipment and practices, harvesting and
storage practices on-farm, transport, storage and processing post farm gate.
Recognising this, almost all traded agricultural commodities accept some degree of
adventitious presence of unwanted material and hence have thresholds set for the presence of
unwanted material. For example, in most cereals, the maximum threshold for the presence of
unwanted material (eg, plant material, weeds, dirt, stones, seeds of other crop species)
commonly used is 2%.
In the European context, the labelling threshold of 0.9% for positive GM labelling has
become the main benchmark for determining the maximum level of adventitious presence of
GM material that is allowed in non GM products
8
. This threshold is considerably more
onerous than, for example, Japan or Korea where the threshold is 5% and 3% respectively.
2.3 Adventitious presence in maize
As indicated above, adventitious presence of GM material in non GM crops can occur for a
variety of reasons. In the case of maize there are three main potential routes through which
adventitious presence may occur.
2.3.1 Cross-pollination
The importance of pollen movement (and the principles behind separation distances) and
possibilities of adventitious presence occurring due to cross-pollination are well researched
and documented (Ingram 2000):
¾
Pollen availability and transmission.
The chances of pollen from a GM crop
pollinating with a non GM crop (ie, introgressing) is a function of the availability and
viability of pollen emitted from the GM crop and its delivery to the stigma of a non
GM plant. Availability of pollen from one variety to another varies due to planting
date and agronomic conditions. The delivery of pollen is influenced by factors such
as wind speed and direction, presence of insect vectors to deliver the pollen, distance,
rainfall and barriers to pollen movement (eg, barrier rows, trees, hedges and
topography);
¾
Degree of cross-pollination.
The efficiency of pollen from a GM plant cross-
pollinating with the non GM plant when it lands on the stigma depends upon a
combinations of factors; timing of flowering of the receptor (non GM) crop needs to
coincide with the GM crop; the GM pollen must still be viable for fertilisation; and
the foreign pollen has to compete with fresher pollen produced by the non GM plant
itself and/or pollen from other non GM plants in the vicinity;
Factors affecting gene expression in the receptor plant.
After cross-pollination the
genetic material is incorporated into the seed and may influence the characteristics of
the resulting seed crop. It does not impact on the integrity of the parts of the non GM
8
Some operators, in some markets, may operate to tighter thresholds but the 0.9% represents the only current
legally enforceable threshold
©PG Economics 2004
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GM maize – pollen movement and crop co-existence
plant, other than the seed (eg, in the case of maize, any introgression of GM material
will show up only in specific kernels of the cob and will not be present in the rest of
the plant);
¾
Inheritance considerations.
Depending on the characteristics of the gene (dominance
pattern and level of heterosis of the commercial hybrid) less than 100% of the emitter
(GM plant derived) pollen will contain the GM trait. Therefore a part of the pollen
produced will
not
contain the GM trait (eg, for Mon 810 insect resistant (Bt) maize
varieties, only 50% of the emitted pollen contains the Bt trait).
As indicated above, the chance of cross-pollination occurring depends upon the availability
and viability of maize pollen to introgress with the receptor maize plant. Maize pollen is
released in very large quantities, between 4.5 and 25 million pollen grains per plant
(Paterniani & Stort, 1974) over a typical 5-8 day period. It remains viable under natural
conditions for about 24 hours, although this can fall to only a few hours in hot, dry weather
or, extend to up to 9 days in cooler, humid conditions (Emberlin, 1999). Compared with other
crop species that rely on the wind to disperse pollen across large distances, maize pollen
grains are relatively large (90-125 µm) and heavy, with a high terminal velocity resulting in
higher comparative deposition (ie, it falls to the ground rapidly in a limited area and does not
travel far
9
). Maize produces pollen before silk emergence ensuring that the majority of maize
plants cross-pollinate with a neighbouring maize plant. However, an overlap between pollen
shedding and silk emergence can occur and up to 5% self-pollination may occur.
The extent to which cross-pollination in maize crops causes problems of adventitious
presence of unwanted material (together with measures to minimise this occurring) are
discussed further in section 3 below.
2.3.2 Seed mediated pollen flow (ie, volunteers)
Volunteers (self sown plants derived from seed of a previous crop) are not an important media
for gene flow in maize. The probability of a volunteer maize crop appearing in subsequent
(maize) crops and then contributing to gene flow via cross pollination from the volunteer to a
maize crop is very low due to the inability of the maize plant to shed seed naturally, a limited
dormancy period, the common use of mechanical pre-planting soil preparation practices and
the inability of maize seed to survive low winter temperatures that often occur in many
(continental) maize growing regions. Even in regions where winter temperatures do not
usually fall to low enough levels to kill off volunteers (eg, Mediterranean countries), they are
not considered to be problematic for growers.
2.3.3 Other possible sources of adventitious presence in maize
Seed purity can affect the levels of adventitious presence, indeed the higher the purity level,
the lower the ‘knock-on’ level in the final product
10
. A few instances have arisen in recent
years where adventitious presence of GM material has been found in some non GM maize
seed. In 2000, for example, some maize seed lots imported into France from North America
were found to have low levels of GMO presence (under 0.2%).
On and off farm storage and handling of seed and crops post harvest also represent possible
opportunities for adventitious presence of GM material being found in non GM maize crops,
especially if crops from GM and non GM growing farms are dried, cleaned and stored in
central (often co-operative) facilities. This has, however not been a problem in countries
9
Defra (2003) Review and knowledge of the potential impacts of GMOs on organic agriculture
10
In the absence of EU legislation for labelling of seed for GM adventitious presence, the EU seed industry
operates to a threshold of 0.5% (ie, non GM maize seed will have less than 0.5% GM adventitious presence)
©PG Economics 2004
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