Mitochondrial heteroplasmy for the cytochrome b gene controls the level of strobilurin resistance in the apple powdery mildew fungus Podosphaera leucotricha (Ell. & Ev.) ES Salmon

In single-spore isolates of the apple powdery mildew fungus Podosphaera leucotricha collected at various sites in Germany, Great Britain and India, we have identified different levels of strobilurin resistance. Sequence analyses of the mitochondrial cytochrome b gene and cleaved amplified polymorphic sequences (CAPS) analyses showed heteroplasmy with respect to the G143A mutation in all isolates tested. The quantity of mitochondria carrying this mutation correlated with strobilurin resistance in germination assays on isolated apple cuticles and in growth assays on strobilurin-treated leaves. In contrast to other plant pathogenic fungi, including powdery mildews of cereals and cucumber, heteroplasmy was stable even after six years of cultivation in the absence of strobilurin fungicides. These data are discussed with respect to disease and fungicide management.