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 unrestri
cted use, distribution, and reproduction in any medium, provided the original author and source are credited.
I think it’s important to note that “as much as 20%” refers to only a single batch of seed – while this clearly isn’t acceptable other batches had either no, or minimal contamination (0.5% was the other batch contamination – 4 of 6 batches had no contamination)
I also find it interesting that while predominantly edges of fields had very low seed % contaminated, and plants 20m in had zero contamination for the most part that in a couple of fields the contamination 20m in was a lot higher than at the edge (1.7% cf .7, 2.6% cf .13% – although sans error bars and whatnot how meaningful these differences are is unknown)
It is also noted later in the paper that seed companies sometimes reject seed lots due to presence of transgenes – which casts some doubt on the opening statement that
even if occasionally production fields become contaminated this doesn’t necessarily mean that these seeds make it to the market – it’d be interesting to see similar numbers for actual production (of cotton) fields rather than seed manufacturing fields.
Without looking at the real numbers, it’s hard to reach firm conclusions.
For instance, it would be possible to detect transgenic seed at a mere 0.05 percent, but in 90 percent of samples. Is that “90 percent contamination”, or is it “0.05 percent contamination”?
In either case, the answer is, “Yes, but…” and the rest is politics.
« In either case, the answer is, “Yes, but…” and the rest is politics. »… And « so what? »
These studies are very interesting, but they miss two things:
1. GM crops – at least those we currently have – are just an addition to the variability we had heretofore. It is no doubt interesting to know how one particular genetic make-up gets into another, but do we really need to spend so much effort because one of them happens to be GM? Aren’t we already familiar with the problem of e.g. conventional maize, sorry corn, pollinating sweet corn?
2. Alright, some variety A (GM) gets mixed into variety B (conventional) seed. The farmer grows his crop, and buys a new batch of seed… End of story, or perhaps the beginning of a new one which will end at the end of the growing season.
The lesson is that seed production and trade must be carefully organised. That is a lesson that we learned a long time ago.
« …we conclude that careful planting and screening of seeds could be more important than field spacing for limiting gene flow. » Bravo, you reinvented the wheel.
« Production-chain management is key issue in GM crop escapes »? No, in seed production and trade.