Effects of thiophanate-methyl and azoxystrobin on the composition of Cercospora kikuchii populations with thiophanate-methyl-resistant strains |
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Authors: | Iori Imazaki Hiromi Iizumi Kouji Ishikawa Masashi Sasahara Nobuko Yasuda Shinzo Koizumi |
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Affiliation: | (1) National Agricultural Research Center, 3-1-1 Kannondai, Tsukuba 305-8666, Japan;(2) Crop Research Center, Niigata Agricultural Research Institute, Nagaoka, Japan;(3) Miyagi Prefecture Furukawa Agricultural Experiment Station, Furukawa, Japan;(4) National Agricultural Research Center for Tohoku Region, Daisen, Japan |
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Abstract: | Azoxystrobin was recently registered in Japan for the control of purple seed stain of soybean caused by Cercospora kikuchii, because the pathogen has developed resistance to thiophanate-methyl. To investigate the effects of these fungicides on the frequency of C. kikuchii strains resistant to thiophanate-methyl and on the genotype structure of the population, we sowed purple-stained seeds, approximately 40% of which were infected with resistant strains, as inocula with asymptomatic seeds and applied thiophanate-methyl and azoxystrobin during the reproductive growth of soybeans. The isolation frequency of resistant strains increased more than 99% by thiophanate-methyl but was not significantly increased by azoxystrobin. In amplified fragment length polymorphism (AFLP) DNA fingerprinting, genotypic diversity was significantly decreased by thiophanate-methyl but was not affected by azoxystrobin. In addition, the similarity of the AFLP genotype structure was increased by thiophanate-methyl but not by azoxystrobin. These results suggest that thiophanate-methyl selectively inhibited the proliferation of sensitive strains, which resulted in a small number of genotypes, most of which were resistant strains. Azoxystrobin was found to nonselectively inhibit proliferation of the pathogen, which retained a large number of genotypes including thiophanate-methyl-sensitive or thiophanate-methyl-resistant strains or both. The nucleotide sequence data for the cytochrome b gene are available in the DDBJ/EMBL/GenBank databases under accession number AB231863. |
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Keywords: | Thiophanate-methyl Azoxystrobin Cercospora kikuchii Genotypic diversity |
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