Isogamous, hermaphroditic inheritance of mitochondrion-encoded resistance to Qo inhibitor fungicides in Blumeria graminis f. sp. tritici.

A mutation of glycine to alanine at position 143 in the mitochondrial cytochrome b amino acid sequence of Blumeria graminis f. sp. tritici cosegregated with the QoI-resistant phenotype in a ratio of 1:1 in a cross between a sensitive and a resistant isolate. This mutation was used as a mitochondrial marker to determine whether mitochondrial inheritance in B. graminis was anisogamous, as in heterothallic Neurospora sp., or isogamous and hermaphroditic, as in Aspergillus nidulans. Segregation of mitochondrial genotypes in B. graminis f. sp. tritici was consistent with inheritance of mitochondria being hermaphroditic and isogamous, in that all ascospores from an individual cleistothecium had the same mitochondrial genotype and that either parent could act as the maternal parent of a cleistothecium. Within each cleistothecium, nuclear segregation occurred independently of mitochondrial inheritance, as shown by segregation of resistance to the fungicide triadimenol and by segregation of avirulences to the wheat cultivars Galahad (Pm2), Armada (Pm4b), and Holger (Pm6).