Genetic control of resistance to tridemorph inustilago maydis |
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Authors: | A N Markoglou B N Ziogas |
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Institution: | (1) Laboratory of Plant Pathology, Agricultural University of Athens, Votanikos, 118 55 Athens, Greece |
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Abstract: | Mutants ofUstilago maydis with low resistance to tridemorph isolated in a mutation frequency of 7x 10-6 after UV-irradiation and selection on media containing 25 μg ml-1 tridemorph. Genetic analysis with nine such mutant isolates resulted in the identification of two unlinked chromosomal loci,U/tdm- 1 andU/tdm- 2. TheU/tdm mutations are responsible for low resistance levels to tridemorph (resistance factor, Rf, of 3 or 5 based on effective concentration
causing a 50% reduction in the growth rate (EC50) or minimal inhibitory concentration (MIC) values, respectively) and low to moderate level of resistance to fenpropimorph
(Rf 10 or 16 based on MIC or EC50, respectively) and fenpropidin (Rf 5 or 11 based on MIC or EC50, respectively). Haploid strains carrying bothU/tdm mutations exhibit higher levels of resistance to the above fungicides, indicating interallelic interaction between nonallelic
genes. Crosses between mutants carrying theU/tdm- genes with compatible isolates carrying theU/fpm- 1 orU/fpm- 2 mutations, which were found in previous work to carry fenpropimorph resistance, yielded in all cases a large number of
recombinants with wild-type sensitivity, indicating that the mutant genes involved were not allelic. Cross-resistance studies
with the inhibitors of C-14 demethylase showed that. the U/tdm-mutations were responsible for increased sensitivity to the
triazoles triadimefon, triadimenol, propiconazole and flusilazole, and to the pyridine pyrifenox. Study of gene effect on
the fitness ofU. maydis showed thatU/tdm-mutations appeared to be pleiotropic, having more or less adverse effects on growth rate in liquid culture and pathogenicity
on young corn plants. |
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Keywords: | Ustilago maydis fungicide resistance tridemorph morpholines ergosterol biosynthesis inhibitors genetic control of resistance |
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