The application of the concept of pathogen derived resistance opened new horizons for the development of virus-resistant plants. In this mechanism, resistance to a virus is engineered in transgenic plants through the expression of a segment of the virus genome. This technique simply improves the development of crops which deliver high yields. On the other hand, there are some concerns about transgenic crops consumption. Also development in pesticides, chemical fertilizers and other technologies related to modern intensive agriculture threaten both human health and environment. Therefore the first step after transgenic plant production is to evaluate its potential benefits and risks to the environment and these should be compared to those generated by traditional agricultural practices. The main ecological concerns that are currently debated are complementation, heterologous encapsidation, synergy, plant-to-plant gene flow by outcrossing, plant-to-virus gene flow by recombination, effect on nontarget organisms, food and feed safety.