title: Resistance to the novel fungicide pyrimorph in Phytophthora capsici: risk assessment and detection of point mutations in CesA3 that confer resistance.
abstract: Pyrimorph is a novel fungicide with high activity against the plant pathogen Phytophthora capsici. We investigated the risk that P. capsici can develop resistance to pyrimorph. The baseline sensitivities of 226 P. capsici isolates, tested by mycelial growth inhibition, showed a unimodal distribution with a mean EC(50) value of 1.4261 (± 0.4002) µg/ml. Twelve pyrimorph-resistant mutants were obtained by repeated exposure to pyrimorph in vitro with a frequency of approximately 1 × 10(-4). The resistance factors of the mutants ranged from 10.67 to 56.02. Pyrimorph resistance of the mutants was stable after 10 transfers on pyrimorph-free medium. Fitness in sporulation, cystospore germination, and pathogenicity in the pyrimorph-resistant mutants was similar to or less than that in the parental wild-type isolates. On detached pepper leaves and pepper plants treated with the recommended maximum dose of pyrimorph, however, virulence was greater for mutants with a high level of pyrimorph resistance than for the wild type. The results suggest that the risk of P. capsici developing resistance to pyrimorph is low to moderate. Among mutants with a high level of pyrimorph resistance, EC(50) values for pyrimorph and CAA fungicides flumorph, dimethomorph, and mandipropamid were positively correlated. This indicated that point mutations in cellulose synthase 3 (CesA3) may confer resistance to pyrimorph. Comparison of CesA3 in isolates with a high level of pyrimorph resistance and parental isolates showed that an amino acid change from glutamine to lysine at position 1077 resulted in stable, high resistance in the mutants. Based on the point mutations, an allele-specific PCR method was developed to detect pyrimorph resistance in P. capsici populations.
authors: Department of Plant Pathology, College of Agriculture and Biotechnology, China Agricultural University, Beijing, China.
authors: Zhili
authors: Z
authors: Pang
authors: Jingpeng
authors: J
authors: Shao
authors: Lei
authors: L
authors: Chen
authors: Xiaohong
authors: X
authors: Lu
authors: Jian
authors: J
authors: Hu
authors: Zhaohai
authors: Z
authors: Qin
authors: Xili
authors: X
authors: Liu
mesh_terms: D000178:Acrylamides / Q000494:pharmacology*; D000595:Amino Acid Sequence; D002212:Capsicum / Q000382:microbiology; D003001:Cloning, Molecular; D025141:Drug Resistance, Fungal / Q000235:genetics*; D005656:Fungal Proteins / Q000235:genetics*; D005659:Fungicides, Industrial / Q000494:pharmacology*; D005964:Glucosyltransferases / Q000235:genetics*; D008826:Microbial Sensitivity Tests; D008969:Molecular Sequence Data; D009025:Morpholines / Q000494:pharmacology*; D025282:Mycelium / Q000187:drug effects / Q000235:genetics / Q000254:growth & development; D010838:Phytophthora / Q000187:drug effects / Q000235:genetics* / Q000254:growth & development; D010935:Plant Diseases / Q000382:microbiology; D018515:Plant Leaves / Q000382:microbiology; D017354:Point Mutation; D018570:Risk Assessment; D036226:Seedlings / Q000382:microbiology; D017422:Sequence Analysis, DNA
chemical_list: D000178:Acrylamides; D005656:Fungal Proteins; D005659:Fungicides, Industrial; D009025:Morpholines; C550850:pyrimorph; D005964:Glucosyltransferases; C478648:cellulose synthase