Production-chain management is key issue in GM crop escapes

posted in: Syndicated | 3

Sloppy seed-sorting main culprit in GM crop escapes
(Press release about a free access PLoS ONE article linked below)
María Elena Hurtado
17 December 2010
IMAGE: Honey bees transmit GM pollen to non-GM fields, but human error plays a bigger role in GM contamination

Careless handling of seeds may be the key reason for the unintended spread of genetically modified (GM) crops, a study has found.

The discovery challenges the widespread belief that the main source of GM contamination is the transfer of pollen by bees from GM crops to non-GM counterparts in neighbouring fields. Human error during seed production and handling is the more likely culprit, say the researchers.

Stands of non-GM crop plants are currently planted near or within fields of modified crops to provide refuges for pests. This technique helps prevent the pests developing resistance to the pesticides used on GM crops. But human error could undermine this widely used strategy, the paper says.

Shannon Heuberger, an entomologist at the University of Arizona, United States, and her colleagues measured the gene flow — the movement of genes between different populations that occurs when a plant from one population fertilises a plant from the other — in Bt (Bacillus thuringiensis) cotton, the widely planted GM crop, in 15 fields in Arizona.

They found that gene flow via the transmission of pollen by bees was rare. Fewer than one per cent of seeds produced by ordinary cotton plants contained genes from Bt cotton that had been transmitted in this way.

But poor seed-sorting resulted in some seed bags intended for planting in non-GM fields containing as much as 20 per cent GM seed. One non-GM field was found to have a large number of GM plants due to human error in planting.

“Our most important result is that growers can minimise gene flow by screening the seed before planting it in seed-production fields and by being more cautious in their planting process,” Heuberger told SciDev.Net.

“In comparison, designing strategies to minimise bee pollination between fields can be quite difficult because insect behaviour is hard to predict,” she added.

The study concludes that seed producers and decision makers should consider screening seeds to monitor the presence of GM seeds in the supply, and that they also need to communicate “the importance of segregating seed types at planting to reduce human error”.

María Isabel Manzur, head of biodiversity at the Sustainable Societies Foundation (FSS), a Chilean environmental non-governmental organisation, said: “This is a very interesting study because it helps elucidate at a greater depth how transgenic contamination takes place”.

“It corroborates once more that transgenic crops can contaminate surrounding crops, which is something that biotech companies frequently deny despite all the evidence to the contrary.”

The study was published in PLoS ONE last month (30 November).

Link to full paper in PLoS ONE

PLoS ONE doi: 10.1371/journal.pone.0014128 (2010)

Pollen- and Seed-Mediated Transgene Flow in Commercial Cotton Seed Production Fields

Characterizing the spatial patterns of gene flow from transgenic crops is challenging, making it difficult to design containment strategies for markets that regulate the adventitious presence of transgenes. Insecticidal Bacillus thuringiensis (Bt) cotton is planted on millions of hectares annually and is a potential source of transgene flow.

Here we monitored 15 non-Bt cotton (Gossypium hirsutum, L.) seed production fields (some transgenic for herbicide resistance, some not) for gene flow of the Bt cotton cry1Ac transgene. We investigated seed-mediated gene flow, which yields adventitious Bt cotton plants, and pollen-mediated gene flow, which generates outcrossed seeds. A spatially-explicit statistical analysis was used to quantify the effects of nearby Bt and non-Bt cotton fields at various spatial scales, along with the effects of pollinator abundance and adventitious Bt plants in fields, on pollen-mediated gene flow. Adventitious Bt cotton plants, resulting from seed bags and planting error, comprised over 15% of plants sampled from the edges of three seed production fields. In contrast, pollen-mediated gene flow affected less than 1% of the seed sampled from field edges. Variation in outcrossing was better explained by the area of Bt cotton fields within 750 m of the seed production fields than by the area of Bt cotton within larger or smaller spatial scales. Variation in outcrossing was also positively associated with the abundance of honey bees.

A comparison of statistical methods showed that our spatially-explicit analysis was more powerful for understanding the effects of surrounding fields than customary models based on distance. Given the low rates of pollen-mediated gene flow observed in this study, we conclude that careful planting and screening of seeds could be more important than field spacing for limiting gene flow.

Shannon Heuberger *, Christa Ellers-Kirk, Bruce E. Tabashnik, Yves Carrière

Department of Entomology, University of Arizona, Tucson, Arizona, United States of America
Abstract
Background

Characterizing the spatial patterns of gene flow from transgenic crops is challenging, making it difficult to design containment strategies for markets that regulate the adventitious presence of transgenes. Insecticidal Bacillus thuringiensis (Bt) cotton is planted on millions of hectares annually and is a potential source of transgene flow.

Methodology/Principal Findings

Here we monitored 15 non-Bt cotton (Gossypium hirsutum, L.) seed production fields (some transgenic for herbicide resistance, some not) for gene flow of the Bt cotton cry1Ac transgene. We investigated seed-mediated gene flow, which yields adventitious Bt cotton plants, and pollen-mediated gene flow, which generates outcrossed seeds. A spatially-explicit statistical analysis was used to quantify the effects of nearby Bt and non-Bt cotton fields at various spatial scales, along with the effects of pollinator abundance and adventitious Bt plants in fields, on pollen-mediated gene flow. Adventitious Bt cotton plants, resulting from seed bags and planting error, comprised over 15% of plants sampled from the edges of three seed production fields. In contrast, pollen-mediated gene flow affected less than 1% of the seed sampled from field edges. Variation in outcrossing was better explained by the area of Bt cotton fields within 750 m of the seed production fields than by the area of Bt cotton within larger or smaller spatial scales. Variation in outcrossing was also positively associated with the abundance of honey bees.
Conclusions/Significance

A comparison of statistical methods showed that our spatially-explicit analysis was more powerful for understanding the effects of surrounding fields than customary models based on distance. Given the low rates of pollen-mediated gene flow observed in this study, we conclude that careful planting and screening of seeds could be more important than field spacing for limiting gene flow.

Citation: Heuberger S, Ellers-Kirk C, Tabashnik BE, Carrière Y (2010) Pollen- and Seed-Mediated Transgene Flow in Commercial Cotton Seed Production Fields. PLoS ONE 5(11): e14128. doi:10.1371/journal.pone.0014128

Editor: Haibing Yang, Purdue University, United States of America

Received: June 18, 2010; Accepted: October 24, 2010; Published: November 30, 2010

Copyright: © 2010 Heuberger et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

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David Tribe is an applied geneticist, teaching graduate/undergrad courses in food science, food safety, biotechnology and microbiology at the University of Melbourne.