Mechanisms of resistance to fenpropimorph and terbinafine, two sterol biosynthesis inhibitors, in Nectria haematococca, a phytopathogenic fungus

Autor: Pierre Leroux, Jocelyne Bach, Danièle Debieu, Alexandrine Lasseron-De Falandre, Christian Malosse
Přispěvatelé: ProdInra, Migration, Unité de phytopharmacie et médiateurs chimiques, Institut National de la Recherche Agronomique (INRA)
Jazyk: angličtina
Rok vydání: 1999
Předmět:
Zdroj: Pesticide Biochemistry and Physiology
Pesticide Biochemistry and Physiology, Elsevier, 1999, 64, pp.167-184
ISSN: 0048-3575
1095-9939
Popis: The mechanisms of resistance to terbinafine, a squalene epoxidase inhibitor, and to fenpropimorph, a sterol Δ 14 -reductase and/or Δ 8 → Δ 7 -isomerase inhibitor, were investigated in laboratory mutants of the phytopathogenic fungus Nectria haematococca . Neither modified fungicide uptake nor fungicide metabolism could explain resistance in the mutants studied. The terbinafine-resistant mutants contained at least 10 times more squalene than the wild-type strain, and when cultivated in presence of terbinafine, they required a 30-times higher fungicide concentration to obtain a very high level of accumulated squalene similar to that of the wild-type strain. Thus, a reduced affinity of the squalene epoxidase toward both the substrate and the fungicide could explain terbinafine resistance in these mutants. In some fenpropimorph-resistant mutants, the effects of fenpropimorph on sterol biosynthesis were similar to those in the wild-type strain, suggesting that resistance could be due to tolerance to sterol Δ 8,14 -sterol accumulation and to Δ 5,7 -sterol decrease. In one of them, the major sterol in absence of fungicide was not ergosterol, but ergosta-5,7,22,24(24 1 )-tetraenol, indicating reduced Δ 24 (24 1 )-reductase activity. The potential role of a modified Δ 24 (24 1 ) reductase in fenpropimorph resistance has yet to be elucidated. In the remaining fenpropimorph-resistant mutants, much higher fenpropimorph concentrations were required to cause ergosterol decreases similar to that in the wild-type strain, suggesting a Δ 14 -reductase modification. Among them, some mutants accumulated Δ 8 -sterols as well as Δ 8,14 -sterols, indicating that the mechanism of resistance may be due to reduced affinity of the Δ 14 -reductase toward fenpropimorph, whereas the other mutants accumulated only Δ 8,14 -sterols. Those last mutants contained much larger amounts of 4,4-dimethyl and 4α-methyl sterols than the wild-type strain, in the absence of fungicide. The most abundant methylated sterol was 4,4-dimethylfecosterol, the presumed product of the Δ 14 -reductase, suggesting that resistance may be due to overproduction of the Δ 14 -reductase in these mutants.
Databáze: OpenAIRE
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