New research results and mistakes in crop trials have added to concerns over the use of genetically modified (GM) crops. A joint French/US team of researchers found in experiments that weeds have been swapping genes with neighbouring genetically modified crops to make themselves stronger. The exchange of genes increased the number of seeds produced by the weeds and sometimes this was to the detriment of the genetically modified crops. The results have raised fears that widespread use of genetically modified crops could lead to weeds which are impossible to control affecting farmers. The tests were carried out on sugar beet in France and sunflowers in the USA, by teams from the universities of Lille and Ohio respectively. Allison Snow, who headed the Ohio team, claimed that the results did not necessarily indicate that GM crops were dangerous, but that she was shocked by the results. The results coincide with the company Pioneer Hi-Bred, which developed the GM sunflower, deciding to pull out of selling the strain commercially. In the UK, an error has led to rogue GM seeds being sewn which were not authorised for planting. Biotech firm, Aventis CropScience admitted that a small quantity of different seeds to those which were intended were included in those they supplied. This may have contaminated the trial of the GM seeds of rapeseed crops being carried out at 14 sites in the UK. But the UK government, while admitting that it was annoyed by the mistake, has said that the trials are still valid and will continue. The rogue seeds contained a gene giving resistance to two antibiotics and have been used in 25 UK trials since 1999. Hendrik Verfaillie, Chief executive of Monsanto, one of the biggest companies involved in the genetically modified crop sector, was reported as saying during August that he did not expect any regulatory approval for its genetically modified products before 2005 in Europe. He added that the company may make further cuts in research.