The genetic resources used across Europe vary to a great extent as very few cultivars are grown in more than one country. All countries have an extensive cultivar testing system but the way of ranking resistance characteristics is quite different across countries. Data from cultivar testing has shown that under high disease pressure even the most resistant cultivars often give profitable yield responses from fungicide treatment. This indicates that the resistance genes, although they help a lot, rarely cover all potential diseases that can attack the crop and the stability of resistant genes are often seen to gradually change over time.
With respect to yellow and brown rust, it is well known that resistant cultivars can completely eliminate the risk from these diseases. This is not seen to the same extent with diseases such as powdery mildew, Septoria leaf blotch, Tan spot and Fusarium head blight, where often only moderate levels of resistance are seen.