Genetics of apple scab resistance to fungicides
Apple scab (Venturia inaequalis) is controlled primarily by application of fungicides. The most important fungicides used, DMIs, act by inhibiting a step (demethylation) in the production of the cell membrane component ergosterol. This group is especially important in the UK because they can control powdery mildew as well as scab. Continued use of DMI fungicides has led in many countries to populations of many pathogens, including V. inaequalis, becoming less sensitive to DMI fungicides. The site of action of the DMI fungicides is the CYP51 protein. Resistance may arise through alteration of the sequence of this protein, or through other adjustments to cell metabolism. The sensitivity of V. inaequalis to DMIs varies continuously over the range found, suggesting that it is controlled genetically by several or many genes or many allelic forms of one or a few genes. Only one of these has been found, which is an alteration in an element controlling the production of CYP51 protein from the CYP51A1 gene.
We are conducting experiments to understand the adaptive landscape in which selection for resistance against myclobutanil in V. inaequalis takes place. In addition, we are also interested in the baseline response to tebuconazole, recently approved for use to control apple scab in the UK.