gene Flow: Implications for Crop Diversity and Wild Relatives

Chapter 3(Trans)gene Flow and Its PotentialEvolutionary ConsequencesSo why might changes in plant fitness (its ability to surviveand reproduce) resulting from transgene flow be significant?Effects on fitness are largely dependent on the nature of thegenetically engineered traits, and the external and internalfactors that influence their expression (Gepts & Papa 2003;Jenczewski et al. 2003). As approximately 97% of all transgeniccrops involve insect resistance or herbicide resistance, theseare the main traits under consideration (yet the history ofunintended transgene flow events, and the coming generationof plant-made pharmaceuticals are perhaps signs of things tocome). In the case of insect resistance transgenes, levels ofpest pressure in wild or landrace populations may be lowercompared to crop populations, reducing the selective value ofthe trait. Herbicide resistance genes might exhibit an energeticcost on the hybridised plant that would have no value if theherbicide is not applied (but alternatively, great value if it is).In the case of stress-tolerant transgenic crops (drought tolerance,salt tolerance, etc.), with traits that allow survival in a broaderrange of ecological conditions, hybridisation is likely to increasefitness and invasiveness.Hence, whether transgenes from a source population willestablish in wild or landrace sink populations will dependon a number of independent and interrelated factors –genetic, ecological and even human management variables.8