QoI resistance development in populations of cereal pathogens in the UK

The effectiveness of strategies aiming to retard the development of resistance to Qo inhibitor fungicides in barley powdery mildew populations was determined with PCR by measuring the frequency of the G143A mutation in cytochrome b. Preliminary results from field trials show that the frequency of the G143A mutation increases with higher doses and increasing number of sprays. Mixtures of fungicides with different modes of action appeared to slow down the increase in the frequency of the mutation. For most locations sampled in the UK, high frequencies of G143A were detected in Septoria tritici populations during spring 2003. Studies are now in progress to establish the significance of G143A in QoI resistance development in populations of S. tritici, and to evaluate anti-resistance strategies for this pathogen.