Roundup drives evolution of tolerance in weeds

Gene flow from transgenic crops to wild populations of weeds are not the only way that weeds can become tolerant to herbicides. The widespread and increasing use of Roundup has favoured natural selection of existing genetic variation in Ipomoea purpurea (morning glory) leading to Roundup tolerant weeds. Scientists at University of Georgia, Athens, USA studied the offspring from I. purpurea collected from fields where Roundup had consistently been used for 8 years. The study emphasized the difference between resistance and tolerance: the weed paid a high price for herbicide tolerance by compensating for damage and developed significantly fewer seeds in absence of Roundup.

Source: Beaucom & Mauricio (28 September 2004) PNAS 101: 13386-13390