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Environmental problems for distinguishing GM seed

Several studies have indicated that NIR spectroscopy can differentiate between the seeds of conventional and genetically-modified (GM) crop varieties, including between conventional and Roundup Ready (RR) soybeans, which are resistant to the herbicide glyphosate. This opens up the possibility of using NIR spectroscopy to test whether conventional seed is contaminated by GM varieties, as a faster and more convenient alternative to current DNA- and antibody-based tests.

There are major doubts, though. Not only has the accuracy of NIR spectroscopy been called into question by certain studies, but no one is sure exactly what chemical differences it is detecting. To find out, US scientists led by Lidia Esteve Agelet from Iowa State University in Ames analysed samples of five different varieties of conventional and RR soybean seeds with NIR spectroscopy. They then related the spectral data to measurements of the seeds’ weight and oil and protein content. Their findings are not very encouraging for those hoping to use NIR spectroscopy to detect GM contamination.

As they report in Food Chemistry, although NIR spectroscopy could distinguish between conventional and RR seeds, there was no significant overall difference in the weight and oil and protein content between the two types of seed. What’s more, NIR spectroscopy was better at distinguishing between conventional and GM seeds of specific varieties, and here there were some differences in the oil and protein content between conventional and RR versions.

Rather unexpectedly, it also turned out that NIR spectroscopy was more accurate at distinguishing between conventional and RR seeds that had a high moisture content, which give Agelet and her team an indication of how NIR spectroscopy is able to distinguish between the two seed types. For the scientists noticed that RR seeds absorb water faster and retain it longer than conventional seeds, which they think is probably due to differences in the structure and chemical composition of the seed hull. So they propose that NIR spectroscopy is picking up these differences.

Unfortunately, these differences in the seed hull between conventional and RR seeds can be completely masked by changes in the moisture content, which is dictated by environmental conditions. So Agelet concludes that NIR spectroscopy is probably not reliable enough to differentiate between conventional and RR seeds out in the real world, where the environmental conditions can’t be controlled.

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