Journal of Phytopathology - Phytopathologische Zeitschrift (2001) 149, 551-559

A.N. Markoglou and B.N. Ziogas (2001)
Genetic control of resistance to the piperidine fungicide fenpropidin in Ustilago maydis
Journal of Phytopathology - Phytopathologische Zeitschrift 149 (9), 551-559
Abstract: Mutants of Ustilago maydis (DC.) Corda, resistant to the piperidine fungicide fenpropidin, were isolated in a mutation frequency of 3.2 × 10^–5, after UV-irradiation and selection on media containing 75 µg/ml fenpropidin. Genetic analysis with 15 such mutant isolates resulted in the identification of two unlinked chromosomal loci, U/fpd-1 and U/fpd-2. The U/fpd mutations are responsible for moderate resistance levels to fenpropidin (Rf: 42–56 or 15 based on effective concentration causing a 50% reduction in the growth rate (EC₅₀) or minimal inhibitory concentration (MIC) values, respectively). Haploid strains carrying both U/fpd mutations do not exhibit higher levels of resistance to fenpropidin, indicating no additivity of gene effect between non-allelic genes. Cross-resistance studies with other Sterol Biosynthesis inhibitors (SBIs) showed that the U/fpd-mutant isolates exhibited a positive cross-resistance to the piperidine piperalin and to the related morpholine fungicides fenpropimorph and tridemorph, but not to the inhibitors of C-14 demethylase and squalene epoxidase. Crosses between mutants carrying the U/fpd-genes with compatible isolates carrying the U/fpm or U/tdm mutations, which have been identified in previous genetic studies for resistance to morpholine fungicides fenpropimorph and tridemorph, yielded, with the exception of U/fpd-2 × U/fpm-2 crosses, a large number of recombinants with wild-type sensitivity, indicating that the mutant genes involved were not allelic. Analysis of progeny from crosses between U/fpd-2 and U/fpm-2 mutants yielded no recombinants with wild-type sensitivity, but a 1 : 1 progeny segregation was observed at the MIC for the U/fpd-2 isolates, indicating that these genes are alleles of the same locus. A study of the fitness of fenpropidin-resistant isolates showed that the U/fpd mutations do not affect the phytopathogenic fitness-determining characteristics such as growth in liquid culture and pathogenicity on young corn plants.
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Database assignments for author(s): Anastasios N. Markoglou, Basil N. Ziogas

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.
	Mycosarcoma maydis		Greece