ACRE Advice

Advice for the National Assembly for Wales

Cross-Pollination in Relation to Farm Scale Evaluations of Genetically Modified Maize in Wales

1 May 2001

Background

The National Assembly for Wales (NAW) is concerned about the impact on organic farming of the farm scale evaluation sites of T25 genetically modified (GM) maize in Wales. The NAW has asked for ACRE's advice on the separation distances for the GM maize as set out in the SCIMAC ¹ code and whether they are adequate in Wales to protect neighbouring maize crops.

The current separation distances for T25 GM maize in the farm scale evaluations are intended to ensure that there is no more than 1% adventitious GM presence in neighbouring maize crops. The SCIMAC Code specifies the following separation distances for T25 maize:

• 80m from GM maize to neighbouring non-organic forage maize;
• 200m to non-organic sweetcorn, seed crops and organic forage maize or sweetcorn.

Assembly officials cite three reasons to re-assess the current SCIMAC separation distances.

First, the Government's Chief Scientific Advisor wrote to Ministers in February 2001 to explain the likely level of adventitious GM presence that could be expected in food/feed chains due to the farm scale evaluation programme in the UK. The CSA estimates that for maize, the GM material in neighbouring non-GM maize fields amounts to 0.0005% of the total maize harvest of 4 million tonnes. The NAW is concerned that whilst this calculation might be correct in terms of UK total production, in Wales where forage maize is mainly used as winter fodder for cattle and is grown for on-farm use, any GM presence will not be diluted by the overall UK crop. Furthermore, sweetcorn goes directly for human consumption and is not mixed with the total maize harvest.

Second, the NAW is concerned that the SCIMAC separation distances may not be adequate to reduce cross-pollination to 1% or less because of the frequent and strong south-westerly winds experienced in SW Wales, coupled with complex topography. These factors may result in higher than anticipated levels of cross-pollination. The National Pollen Research Unit estimates ² that cross-pollination could be as high as 2 percent at a separation distance of 80 meters and in excess of 1 percent at 200m.

Third, the Scientific Committee on Plants (SCP) have recently advised ³ that the current Commission proposal for thresholds of 0.3% to 0.5% GM presence in conventional seed lots is so stringent as to be unworkable, and casts doubt on the robustness of achieving a 1% threshold reliably in cases where GM crops are grown on a commercial scale.

Against this background ACRE offers the following advice to the National Assembly

ACRE's advice

ACRE is confident that, based on the best available information in the scientific and plant breeding literature, the SCIMAC separation distances for GM maize (var. Chardon LL), as used in the farm scale evaluations, are robust. The purpose of the separation distance is not an issue of safety, but to minimise adventitious GM presence in neighbouring compatible crops. ACRE's view of the likely upper limit of adventitious GM in neighbouring maize crops due to cross-pollination at the SCIMAC separation distances is summarised in the table below:

*the amount of GM material in animal forage (silage) as a result of cross-pollination will be less than that in the cobs of sweetcorn at the same separation distance. This is because cross-pollination only affects the composition of the grains (kernels in the cobs) and not the leaves or stems. Silage made from chopped maize plants rarely exceeds 50% grain by weight.

These figures for GM maize take into account the nature of the crop (this variety of T25 is heterozygous for the GM insert so only half of the pollen grains carry the GM trait) and practical plant breeding experience over many years. They are based on field experiments ⁴ designed to ensure that cross-pollination occurs at the highest recorded level and that factors, such as prevailing wind direction and strength, favour cross-pollination. The levels of adventitious GM presence in neighbouring maize crops and products will be considerably below this in almost all field situations at these distances. It is well known that the rate of cross-pollination between different yet compatible crop varieties falls very rapidly to low levels over the first few metres of separation, and declines more slowly thereafter. This has been used for many years as the basis for designing field plots for the production of seeds of crop varieties that meet high standards of purity (typically >99% pure).

ACRE notes that the closest organic holding to a GM maize farm scale evaluation site in Wales is that at Mathry, Pembrokeshire, which is approximately 650 meters to the nearest boundary. It is not know whether organic sweetcorn or forage maize is to be grown on this holding but ACRE advises that at the minimum distance of 650m any cross-pollination will be significantly less than 0.1%. This figure allows for the local geography, prevailing wind direction and its likely strength in this area.

ACRE was also asked to consider the issue of 'harm' as defined in Section 107(6) of the Environmental Protection Act 1990. ACRE acknowledges that the definition of harm in this context involves both legal interpretation and scientific assessment. ACRE is not constituted to advise on points of law, but it has recently embarked on a detailed consideration of the scientific and biological definition of harm as applied to the deliberate release of GMOs. This is a complex issue and considered advice and guidance is likely to be available towards the end of 2001. However, ACRE considers, on the basis of its previous deliberations, together with those of EU Member States, that the cultivation of T25 maize on the Welsh sites will have no more direct impact on the natural environment than equivalent non-GM maize. Assessing the significance of any indirect effects associated with the growing of the herbicide tolerant crops with the associated herbicides is the aim of the farm scale evaluations themselves.

Consideration:

In reaching its view on separation distances for GM maize ACRE reviewed a number of issues and sources of information. The main document was the NIAB report of August 2000 on the relationship between separation distances and levels of crop purity. ACRE was also aware of subsequent correspondence from the author of this report that added to and clarified the maize data ⁵.

The NIAB report draws on the current scientific literature and practical experience of plant breeding over many years to recommend separation distances between GM and compatible crops that will deliver no more than 1%, 0.5% or 0.1% adventitious GM presence due to cross-pollination in neighbouring crop or products. The SCIMAC separation distances are based on the NIAB recommendations.

ACRE agrees with the conclusions drawn in the NIAB report and supports the recommended separation distances, which the Committee advises are based on the best available evidence and are compatible with international seed certification schemes accepted by EC, OECD and US authorities.

ACRE therefore independently endorses the following separation distance data for GM maize:

*The table refers to varieties of GM maize, such as that used in the farm scale evaluations, which are heterozygous for the GM trait. For any homozygous varieties the amount of GM presence will be approximately double the above figures at the same separation distances.

The recommended distances are based on conditions that favour cross-pollination (adjacent fields with long sides abutting, where the field is down wind of the pollen source and strong dry winds prevail) and may be regarded as a robust upper limit. Data were collected mainly in the USA, but also in other regions of the world and varying topography and climate. There is no reason to believe that the figures are not equally applicable to Wales.

It must be recognised, however, that it is impossible to give an absolute guarantee that cross-pollination will never exceed the expected level, and there may be rare situations, such as pollen carried by wind funnelled down a valley, that lead to a localised higher level of cross-pollination. Notwithstanding rare events, there is good evidence ⁶ that landscape features, for example hedges, trees and hills do much to reduce cross-pollination rather than increase it.

It is ACRE's view that the separation distances and levels of cross-pollination as set out above are not called into question by the report from the National Pollen Research Unit. ACRE has given detailed advice on this report previously ⁷. The report is a review of the published information on maize pollen dispersal and ACRE accepts that pollen may be carried on air currents for great distances, but pollen dispersal is not the primary issue. The main consideration is the frequency at which that dispersed pollen results in successful cross-pollination. The NPRU report calculates theoretical cross-pollination levels and is not based on the diversity of practical field experience available in the literature.

Nor are the separation distances affected by the Government Chief Scientific Advisor's views on the likely level of adventitious GM presence in food/feed chains due to the farm scale evaluations. The Committee agrees that the CSA's dilution calculation, although applicable to commodity maize crops, does not apply to forage maize that is used on-farm or to sweetcorn which is sold on the cob. Nevertheless, there is nothing in the CSA's note that calls into question the current state of scientific knowledge regarding cross-pollination of maize crops.

ACRE has also considered the opinion of the Scientific Committee on Plants that the current Commission proposal for thresholds of 0.3% to 0.5% GM presence is so stringent as to be unworkable. The SCP's also casts doubt on the robustness of achieving a 1% threshold reliably in cases where GM crops are grown on a commercial scale. The SCP's comments were not directed at the farm scale evaluation programme nor at the SCIMAC guidelines, but refer to a situation where cultivation of GM crops is widespread in the absence of separation distances. ACRE agrees that in future the widespread cultivation of GM maize without separation distances similar to those employed in the farm scale evaluations will to lead to difficulties in maintaining crop purity. However, these concerns do not add new scientific information or question the reliability of the separation distances used in the farm scale evaluations.

1 Supply Chain Initiative on Modified Agricultural Crops guidelines for growing herbicide tolerant crops in the UK

2 Emberlin J., Adams-Groom, B. Tidmarsh, J. (1999) A Report on the Dispersal of Maize Pollen. National Pollen Research Unit, University College, Worcester.

3 Opinion of the Scientific Committee on Plants concerning the Adventitious presence of GM seeds in Conventional Seeds. SCP/GMO-seed-cont/002-final. Published on 13 March 2001

4 Report on the separation distances required to ensure cross-pollination is below specified limits in non-seed crops of sugar beet, maize and oilseed rape. J. Ingram. National Institute of Agricultural Botany. Published 3 August 2000.

5 Subsequent to the published report, NIAB clarified the advice in respect of the separation distance for maize following confirmation that the variety being grown in the FSE is heterozygous. Only half the pollen of such a variety will be GM, and therefore only half of any resultant cross-pollination events will transfer the GM trait, when compared to homozygous varieties on which NIAB had based the original assessment.

6 See NIAB report and further citations therein.

7 www.defra.gov.uk/environment/acre/index.htm