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- Title
Occurrence of boscalid resistance in cucumber powdery mildew in Japan and molecular characterization of the iron–sulfur protein of succinate dehydrogenase of the causal fungus.
- Authors
Miyamoto, Takuya; Ishii, Hideo; Tomita, Yasunori
- Abstract
A total of 74 mass isolates of cucumber powdery mildew fungus ( Podosphaera xanthii) were collected from commercial greenhouses with a history of boscalid use in Ibaraki Prefecture, Japan, and tested in a leaf disk assay for their sensitivity to boscalid. The mildew development of 40 of 74 isolates and five sensitive reference isolates on the disks was completely suppressed at 5 μg boscalid/ml. The minimum inhibitory concentrations (MIC) for the remaining 34 isolates were 50 μg/ml or higher, and 21 of these isolates also grew well at 500 μg/ml. Six single-spore isolates were resistant to boscalid with MIC values higher than 500 μg/ml; four of these were moderately resistant (MR), and two were very highly resistant (VHR) isolates. The growth of MR isolates was almost completely suppressed at 500 μg/ml, whereas two VHR isolates grew vigorously at 500 μg/ml. In foliar inoculation tests of potted cucumber plants, the efficacy of boscalid (500 μg/ml) against both MR and VHR isolates was very low. Partial DNA fragment of the iron–sulphur protein subunit ( SdhB) gene of succinate dehydrogenase was PCR-amplified from five sensitive and five resistant isolates and directly sequenced, revealing that VHR isolates possess a substitution from a highly conserved histidine (CAT) to tyrosine (TAT) in a third cysteine-rich center of a putative SdhB, whereas MR isolates so far have not been found to have such substitution in SdhB.
- Subjects
IBARAKI-shi (Japan); JAPAN; MILDEW; POWDERY mildew diseases; PODOSPHAERA; GREENHOUSES
- Publication
Journal of General Plant Pathology, 2010, Vol 76, Issue 4, p261
- ISSN
1345-2630
- Publication type
Article
- DOI
10.1007/s10327-010-0248-z