Search

BACKGROUND: Didymella bryoniae has a history of developing resistance to single-site fungicides. A recent example is with the succinate-dehydrogenase-inhibiting fungicide (SDHI) boscalid. In laboratory assays, out of 103 isolates of this fungus, 82 and seven were found to be very highly resistant (BVHR) and highly resistant (BHR) to boscalid respectively. Cross-resistance studies with the new SDHI penthiopyrad showed that the BVHR isolates were only highly resistant to penthiopyrad (BVHR-PHR), while the BHR isolates appeared sensitive to penthiopyrad (BHR-PS). In this study, the molecular mechanism of resistance in these two phenotypes (BVHR-PHR and BHR-PS) was elucidated, and their sensitivity to the new SDHI fluopyram was assessed. RESULTS: A 456 bp cDNA amplified fragment of the succinate dehydrogenase iron sulfur gene ( DbSDHB) was initially cloned and sequenced from two sensitive (BS-PS), two BVHR-PHR and one BHR-PS isolate of D. bryoniae. Comparative analysis of the DbSDHB protein revealed that a highly conserved histidine residue involved in the binding of SDHIs and present in wild-type isolates was replaced by tyrosine (H277Y) or arginine (H277R) in the BVHR-PHR and BHR-PS variants respectively. Further examination of the role and extent of these alterations showed that the H/Y and H/R substitutions were present in the remaining BVHR-PHR and BHR-PS variants respectively. Analysis of the sensitivity to fluopyram of representative isolates showed that both SDHB mutants were sensitive to this fungicide as the wild-type isolates. CONCLUSION: The genotype-specific cross-resistance relationships between the SDHIs boscalid and penthiopyrad and the lack of cross-resistance between these fungicides and fluopyram should be taken into account when selecting SDHIs for gummy stem blight management. Copyright © 2011 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Highly iprodione- and fludioxonil-resistant field and laboratory isolates ofA. brassicicolawere found to be either moderately sensitive or tolerant to osmotic stress.AbNIK1, a two-component histidine kinase gene, was isolated from a fungicide-sensitive strain. The predicted protein possessed the six tandem amino acid repeats at the N-terminal end, which is a landmark of osmosensor histidine kinases from filamentous fungi. A comparison of the nucleic acid sequences of theAbNIK1gene from fungicide-sensitive and fungicide-resistant isolates revealed the presence of mutations in six of the seven resistant strains analyzed. Null mutants were all found to be moderately sensitive to osmotic stress, indicating that they are similar toNeurospora crassaType Ios-1mutants. Only one mutation, corresponding to a single amino acid change within the H-box of the kinase domain, was found in an osmotolerant strain. These results suggest that AbNIK1p participates in osmoregulation and that expression of the fully functional enzyme is essential for dicarboximide and phenylpyrrole antifungal activities. [ABSTRACT FROM AUTHOR]