Pest Management Science (2000) 56, 833-841

Helge Sierotzki, Sandro Parisi, Ute Steinfeld, Isabel Tenzer, Sylvie Poirey and Ulrich Gisi (2000)
Mode of resistance to respiration inhibitors at the cytochrome bc₁ enzyme complex of Mycosphaerella fijiensis field isolates
Pest Management Science 56 (10), 833-841
Abstract: Field isolates of Mycosphaerella fijiensis, causing black Sigatoka of banana, were characterised for their sensitivity to different inhibitors of the cytochrome bc₁ enzyme complex (Qo respiration inhibitors, strobilurin fungicides), using physiological, biochemical and molecular genetic methods. Strobilurin-resistant isolates exhibited very high resistance factors both in mycelial growth inhibition and NADH consumption assays. Cross-resistance was observed among all Qo inhibitors, including trifloxystrobin, azoxystrobin, famoxadone, strobilurin B and myxothiazol. However, the Qi and the cytochrome aa₃ inhibitors, antimycin A and potassium cyanide, respectively, were not cross-resistant to Qo inhibitors. In sensitive but not in resistant isolates, mixtures of Qo inhibitors and SHAM, an inhibitor of the alternative oxidase (AOX), were more active than the components alone, indicating that the alternative pathway is essential in metabolism, but not causal for resistance. In the cell-free NADH-consumption assay, the Qo inhibitors affected the sensitive but not the resistant isolates, suggesting that AOX was not active in sub-mitochondrial particles. In whole cells, however, the AOX has a basic expression level and is probably not inducible by trifloxystrobin. Sequencing of the cytochrome b gene of sensitive and resistant M fijiensis isolates revealed a difference in the nucleotide sequence leading to a single amino acid change from glycine to alanine at position 143 in the resistant isolate. This change is known to occur also in the naturally tolerant basidiomycete Mycena galopoda. It is suggested that the field isolates of M fijiensis can acquire resistance to Qo inhibitors due to a target site alteration with a single base pair change. Resistant isolates do not seem to contain a mixture of mutated and non-mutated DNA, indicating a complete selection of resistant mitochondria and a maternally donated mode of resistance.
(The abstract is excluded from the Creative Commons licence and has been copied with permission by the publisher.)
Database assignments for author(s): Helge Sierotzki, Ulrich Gisi

Research topic(s) for pests/diseases/weeds:
pesticide resistance of pest

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Pest and/or beneficial records:

Beneficial	Pest/Disease/Weed	Crop/Product	Country	Quarant.
	Pseudocercospora fijiensis