title: Assessing the risk of resistance in Pseudoperonospora cubensis to the fungicide flumorph in vitro.
abstract: BACKGROUND
  The oomycete fungicide flumorph is a recently introduced carboxylic acid amide (CAA) fungicide. In order to evaluate the risk of developing field resistance to flumorph, the authors compared it with dimethomorph and azoxystrobin with respect to the ease of obtaining resistant isolates to these fungicides, the level of resistance and their fitness in the laboratory.
  
  
  RESULTS
  Mutants with a high level of resistance to azoxystrobin were isolated readily by adaptation and UV irradiation, and their fitness was as good as that of the parent isolates. Attempts to generate mutants of Pseudoperonospora cubensis (Burk. & MA Curtis) Rostovsev resistant to flumorph and dimethomorph by sporangia adaptation on fungicide-treated leaves were unsuccessful. However, moderately resistant mutants were isolated using UV mutagenesis, but their resistance level [maximum resistance factor (MRF) < 100] was much lower than that of the azoxystrobin-resistant mutant (MRF = 733). With the exception of stability of resistance, all mutants showed low pathogenicity and sporulation compared with wild-type isolates and azoxystrobin-resistant mutants. There is cross-resistance between flumorph and dimethomorph, suggesting that they have the same resistance mechanism.
  
  
  CONCLUSIONS
  The above results suggest that the resistance risk of flumorph may be similar to that of dimethomorph but lower than that of azoxystrobin and can be classified as moderate. Thus, it can be managed by appropriate product use strategies.
authors: Department of Plant Pathology, China Agricultural University, Beijing 100094, China.
authors: Shusheng
authors: S
authors: Zhu
authors: Pengfei
authors: P
authors: Liu
authors: Xili
authors: X
authors: Liu
authors: Jianqiang
authors: J
authors: Li
authors: Shankui
authors: S
authors: Yuan
authors: Naiguo
authors: N
authors: Si
mesh_terms: D018553:Cucumis sativus / Q000382:microbiology; D025141:Drug Resistance, Fungal / Q000235:genetics; D005659:Fungicides, Industrial / Q000633:toxicity*; D008689:Methacrylates / Q000633:toxicity; D009025:Morpholines / Q000633:toxicity*; D009154:Mutation; D009868:Oomycetes / Q000187:drug effects* / Q000235:genetics / Q000254:growth & development / Q000472:pathogenicity; D018515:Plant Leaves / Q000382:microbiology; D011743:Pyrimidines / Q000633:toxicity; D012641:Selection, Genetic; D000073739:Strobilurins; D014466:Ultraviolet Rays
chemical_list: D005659:Fungicides, Industrial; D008689:Methacrylates; D009025:Morpholines; D011743:Pyrimidines; D000073739:Strobilurins; C528737:flumorph; C076154:dimethomorph; C087670:azoxystrobin