Annotated Bibliography Entry

Reference: EEA 2002 
Title:  Genetically modified organisms (GMOs): The significance of gene flow through pollen transfer
Authors: Eastham, K. and Sweet, J. and participants in the ESF Assessing the Impact of GM Plants (AIGM) programme
Publisher: European Environment Agency (EEA), Kongens Nytorv 6, DK-1050 Copenhagen K, Denmark
Publication details: 2002, 75p

Summary
            Gene flow from crop types
          Implications and recommendations
Table of Contents

Back to EEA page

 

Summary

In 2000 the EEA established a special project for the European Parliament, on the dissemination of research results from technologies characterised by scientific complexity and uncertainty. The project will support the EEA in its work of helping to develop appropriate monitoring and data sources on the impacts of complex economic/ environment interactions. This is the first report from the project, prepared by the EEA in cooperation with the European Science Foundation (ESF) and its research programme on  Assessing the Impact of GM Plants (AIGM), which was established in 1999.

The ESF/AIGM programme brings together scientists from 10 European countries involved in assessing the environmental and agronomic impact of GM crops, including studies of gene flow and dispersal through pollen, hybridisation and gene introgression. The AIGM programme was invited by the ESF to produce this review of pollen mediated transgene flow based on recent research by participants in the AIGM programme as well as from published reports.

This report considers the significance of pollen-mediated gene flow from six major crop types that have been genetically modified and are close to commercial release in the European Union. Oilseed rape, sugar beet, potatoes, maize, wheat and barley are reviewed in detail using recent and current research findings to assess their potential environmental and agronomic impacts. There is also a short review on the current status of GM fruit crops in Europe. Each crop type considered has its own distinctive characteristics of pollen production, dispersal and potential outcrossing, giving varying levels of gene flow.

Back to top

Gene flow from crop types

Oilseed rape can be described as a high-risk crop for crop-to-crop gene flow and from crop to wild relatives. At the farm scale low levels of gene flow will occur at long distances and thus complete genetic isolation will be difficult to maintain. This particularly applies to varieties and lines containing male sterile components, which will outcross with neighbouring fully fertile GM oilseed rape at higher frequencies and at greater distances than traditional varieties. Gene stacking in B. napus has been observed in crops and it is predicted that plants carrying multiple resistance genes will become common post-GM release and consequently GM volunteers may require different herbicide management. Oilseed rape is cross compatible with a number of wild relatives and thus the likelihood of gene flow to these species is high.

Sugar beet can be described as medium to high risk for gene flow from crop to crop and from crop to wild relatives. Pollen from sugar beet has been recorded at distances of more than 1 km at relatively high frequencies. Cross-pollination in root crops is not usually considered an issue since the crop is harvested before flowering. However a small proportion of plants in a crop will bolt and transgene movement between crops may occur in this way. Hybridisation and introgression between cultivated beet and wild sea beet has been shown to occur.

Potatoes can be described as a low risk crop for gene flow from crop to crop and from crop to wild relatives. Cross-pollination between production crops is not usually considered an issue since the harvested tuber is not affected by incoming pollen. In true seed production areas, however, the likelihood of cross-pollination between adjacent crops leading to contamination is higher. The risk of gene flow exists if volunteers are allowed to persist in a field from one crop to the next. Naturally occurring hybridisation and introgression between potato and its related wild species in Europe is unlikely.

Maize can be described as a medium to high-risk crop for gene flow from crop to crop. Evidence suggests that GM maize plants would cross-pollinate non-GM maize plants up to and beyond their recommended isolation distance of 200 m. There are no known wild relatives in Europe with which maize can hybridise.

Wheat can be described as a low risk crop for gene flow from crop to crop and from crop to wild relatives. Cross-pollination under field conditions normally involves less than 2 % of all florets so any outcrossing usually occurs with adjacent plants. Hybrids formed between wheat and several wild barley and grass species generally appear to be restricted to the first generation with little evidence for subsequent introgression due to sterility.

Barley can be described as a low risk crop for gene flow from crop to crop and from crop to wild relatives. Barley reproduces almost entirely by self-fertilisation, producing small amounts of pollen so that most outcrossing occurs between closely adjacent plants. There are no records of naturally occurring hybrids between barley and any wild relatives in Europe.

Some fruit crops, such as strawberry, apple, grapevine and plum have outcrossing and hybridisation tendencies that suggest that gene flow from GM crops to other crops and to wild relatives is likely to occur. For raspberry, blackberry and blackcurrant the likelihood of gene flow is less easy to predict, partly due to lack of available information.

In summary, different crop species have different rates of autogamy (self pollination) and outcrossing. In addition some crops have hybridising wild relatives in Europe while others do not. The characteristics of the main crop types crops when cultivated in Europe are summarized below: 

·   Oilseed rape is a high-risk crop for crop-to-crop gene flow and from crop to wild relatives.
·   Sugar beet is a medium to high-risk crop for gene flow from crop to crop and from crop to wild relatives.
·   Potatoes is a low risk crop for gene flow from crop to crop and from crop to wild relatives.
·   Maize is a medium to high-risk crop for gene flow from crop to crop.  There are no known wild relatives in Europe with which maize can hybridise.
·   Wheat is a low risk crop for gene flow from crop to crop and from crop to wild relatives.
·   Barley is a low risk crop for gene flow from crop to crop and from crop to wild relatives.
·   Fruit crops, such as strawberry, apple, grapevine and plum have outcrossing and hybridisation tendencies that suggest that gene flow from GM crops to other crops and to wild relatives are likely to occur. For raspberry, blackberry and blackcurrant the likelihood of gene flow is less easy to predict.

Back to top

Implications: The environmental and agronomic impact of gene flow depends on the specific trait/plant combination and the likelihood that gene transfer will occur. (Risk = Hazard/ impact x frequency).  For example: Environmental fitness genes in frequently outcrossing species present the highest risk; environmentally neutral genes in inbreeding species present the lowest risk.

Recommendations: The report makes five recommendations on the implications of gene flow through pollen transfer in European agriculture:

• Gene transfer through cross pollination can be limited by effective biological and physical barriers. More research is needed to examine the options for these in the light of recommendations from the EU on thresholds for contamination of non-GM crops.

• Transgene introgression into wild species is often associated with hybridizing ability. However research has shown that there are physiological barriers operating that inhibit adoption of genes in wild species or populations. Research is needed on actual levels of gene transfer into wild populations from crops and factors involved in genes being adopted by wild populations.

• Both temporal as well as spatial gene flow also arises through seed persistence and dispersal. More information is needed on the role of seed banks and dispersed seed of GM crops on contamination of subsequent crops.

• Better management systems and stewardship schemes to minimise GM contamination and gene flow require good scientific information on both seed and pollen mediated gene flow.

• Future monitoring of experimental and commercial releases of GM crops must be based on good scientific knowledge of the behaviour and ecology of the GM crop and its wild relatives. Understanding gene flow and introgression is a key part of this requirement.

At present none of these crops has pollen that can be completely contained. This means that the movement of seed and pollen will have to be measured and managed much more in the future. Management systems such as spatial and temporal isolation can be used to minimise direct gene flow between crops, and to minimise seed bank and volunteer populations. The use of isolation zones, crop barrier rows and other vegetation barriers between pollen source and recipient crops can reduce pollen dispersal, although changing weather and environmental conditions mean that some long distance pollen dispersal will occur. Biological containment measures are being developed that require research in order to determine whether plant reproduction can be controlled to inhibit gene flow through pollen and/or seed.

The possible implications of hybridisation and introgression between crops and wild plant species are so far unclear because it is difficult to predict how the genetically engineered genes will be expressed in a related wild species. The fitness of wild plant species containing introgressed genes from a GM crop will depend on many factors involving both the genes introgressed and the recipient ecosystem. While it is important to determine frequencies of hybridisation between crops and wild relatives, it is more important to determine whether genes will be introgressed into wild populations and establish at levels that will have a significant ecological impact.

For further information go to Annex: Implications of Pollen Movement from Six Selected Crops in Europe 

Back to top

 

EEA 2002. Genetically modified organisms (GMOs): The significance of gene flow through pollen transfer

Table of Contents

Executive summary 7

Project summary 9

1. Introduction 10
1.1. Aims and objectives of the report 10
1.2. Background10
1.3. Factors affecting pollen dispersal and cross-pollination 11
1.4. Hybridisation, gene flow and introgression 12
1.5. Routes of transgene movement between species 13

2. Oilseed rape ( Brassica napus ssp. oleifera) with reference to turnip rape ( Brassica rapa) 15
2.1. Reproductive biology and crop use 15
2.2. Genetic modification 15
2.3. Pollen dispersal 16
2.4. Gene flow: Crop to crop 17
2.5. Gene flow: Crop to wild relative 21
2.6. Conclusion  26

3. Sugar beet and fodder beet (Beta vulgaris ssp. vulgaris) 27
3.1. Reproductive biology and crop use 27
3.2. Genetic modification  27
3.3. Pollen dispersal  27
3.4. Gene flow: Crop to crop 28
3.5. Definition and status as a weed plant 29
3.6. Gene flow: Crop to wild relative 30
3.7. Conclusion  32

4. Potato ( Solanum tuberosum) 34
4.1. Reproductive biology and crop use 34
4.2. Genetic modification 34
4.3. Pollen dispersal 35
4.4. Gene flow: Crop to crop 35
4.5. Definition and status as a weed plant 36
4.6. Gene flow: Crop to wild relative 36
4.7. Conclusion 37

5. Maize (Zea mays) 38
5.1. Reproductive biology and crop use 38
5.2. Genetic modification 38
5.3. Pollen dispersal 38
5.4. Gene flow: Crop to crop 39
5.5. Definition and status as a weed plant 41
5.6. Gene flow: Crop to wild relative  41
5.7. Conclusion 42

6. Wheat (Triticum aestivum) 43
6.1. Reproductive biology and crop use  43
6.2. Genetic modification 43
6.3. Pollen dispersal  44
6.4. Gene flow: Crop to crop 44
6.5. Definition and status as a weed plant  45
6.6. Gene flow: Crop to wild relative  45
6.7. Conclusion  45

7. Barley (Hordeum vulgare) 46
7.1. Reproductive biology and crop use  46
7.2. Genetic modification  46
7.3. Pollen dispersal  46
7.4. Gene flow: Crop to crop 47
7.5. Definition and status as a weed plant 48
7.6. Gene flow: Crop to wild relative 48
7.7. Conclusion 49

8. Fruit crops 50
8.1. Strawberries (Fragaria x ananassa) 50
8.2. Apples (Malus x domestica) 51
8.3. Grapevines (Vitis vinifera) 51
8.4. Plums (Prunus domestica) 52
8.5. Blackberries (Rubus fruticosus) and raspberries (Rubus idaeus) 53
8.6. Blackcurrants (Ribes nigrum) 54

9. Evaluation and conclusions  56
9.1. Oilseed rape  56
9.2. Sugar beet 56
9.3. Potato 57
9.4. Maize 57
9.5. Wheat 58
9.6. Barley 58
9.7. Fruit crops 58

10. Future considerations and recommendations 59
10.1.Gene flow: Crop to crop 59
10.2.Gene flow: Crop to wild relatives 59
10.3.Gene flow barriers 60

Acknowledgements 62

References 63

Appendix: Assessment of the impacts of genetically modified plants (AIGM) 74  

Back to top

Web site: http://reports.eea.eu.int/environmental_issue_report_2002_28/en