Department of Plant Pathology, College of Agriculture and Biotechnology, China Agricultural University, Beijing, China.
PLoS One. 2013;8(2):e56513. doi: 10.1371/journal.pone.0056513. Epub 2013 Feb 19.
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.
吡嘧肟是一种新型杀菌剂，对辣椒疫霉菌具有高活性。我们研究了辣椒疫霉菌对吡嘧肟产生抗药性的风险。通过菌丝生长抑制试验对 226 个辣椒疫霉菌分离株进行了基线敏感性测试，结果显示敏感性呈单峰分布，平均 EC（50）值为 1.4261（±0.4002）µg/ml。通过在体外反复接触吡嘧肟，大约 1×10（-4）的频率获得了 12 个吡嘧肟抗性突变体。突变体的抗性因子范围为 10.67 至 56.02。突变体在无吡嘧肟的培养基上连续传代 10 次后，其抗性仍稳定。在突变体中，产孢、孢囊萌发和致病性与亲本野生型分离物相似或低于野生型。然而，在离体辣椒叶片和用推荐的最大吡嘧肟剂量处理的辣椒植株上，高水平吡嘧肟抗性突变体的毒力大于野生型。结果表明，辣椒疫霉菌对吡嘧肟产生抗药性的风险为低至中度。在高水平吡嘧肟抗性的突变体中，吡嘧肟和 CAA 杀菌剂氟吗啉、烯酰吗啉和缬菌胺的 EC（50）值呈正相关。这表明纤维素合酶 3（CesA3）的点突变可能导致对吡嘧肟的抗性。对高水平吡嘧肟抗性分离株和亲本分离株的 CesA3 进行比较，发现第 1077 位的谷氨酰胺突变为赖氨酸导致突变体产生稳定的高抗性。基于这些点突变，开发了一种等位基因特异性 PCR 方法，用于检测辣椒疫霉菌群体中的吡嘧肟抗性。
