Department of Plant, Soil, and Microbial Sciences, Michigan State University, East Lansing, MI 48824.
Northwest Michigan Horticultural Research Center, Traverse City, MI 49684.
Plant Dis. 2021 Apr;105(4):958-964. doi: 10.1094/PDIS-07-20-1561-RE. Epub 2021 Feb 17.
Resistance to sterol demethylation inhibitor (DMI) fungicides in , causal agent of brown rot of stone fruit, has been reported in the southeastern and eastern United States and in Brazil. DMI resistance of some isolates, in particular those recovered from the southeastern United States, is associated with a sequence element termed "Mona" that causes overexpression of the cytochrome demethylase target gene . In this study, we conducted statewide surveys of Michigan stone fruit orchards from 2009 to 2011 and in 2019, and we determined the sensitivity to propiconazole of a total of 813 isolates of . A total of 80.7% of Michigan isolates were characterized as resistant to propiconazole by relative growth assays, but the Mona insert was not uniformly detected and was present in some isolates that were not characterized as DMI resistant. Gene expression assays indicated that elevated expression of was only weakly correlated with DMI resistance in isolates from Michigan, and there was no obvious correlation between the presence of the Mona element and elevated expression of . However, sequence analysis of from 25 DMI-resistant isolates did not reveal any point mutations that could be correlated with resistance. Amplification and sequencing upstream of resulted in detection of DNA insertions in a wide range of isolates typed by DMI phenotype and the presence of Mona or other unique sequences. The function of these unique sequences or their presence upstream of cannot be correlated to a DMI-resistant genotype at this time. Our results indicate that DMI resistance was established in Michigan populations of by 2009 to 2011, and that relative resistance levels have continued to increase to the point that practical resistance is present in most orchards. In addition, the presence of the Mona insert is not a marker for identifying DMI-resistant isolates of in Michigan.
石果褐腐病菌对甾醇脱甲基抑制剂（DMI）杀菌剂的抗性已在美国东南部和东部以及巴西报道。一些 分离株的 DMI 抗性，特别是从美国东南部恢复的分离株，与一个称为“Mona”的序列元件相关，该元件导致细胞色素脱甲基酶靶基因 的过度表达。在这项研究中，我们于 2009 年至 2011 年以及 2019 年对密歇根州的石果果园进行了全州范围的调查，并确定了总共 813 株 的对丙环唑的敏感性。通过相对生长测定，密歇根州的分离株共有 80.7%被表征为对丙环唑具有抗性，但 Mona 插入物并未均匀检测到，并且存在于一些未被表征为 DMI 抗性的分离株中。基因表达测定表明，在来自密歇根州的 分离株中， 的表达升高仅与 DMI 抗性弱相关，并且 Mona 元件的存在与 的表达升高之间没有明显的相关性。然而，对 25 个 DMI 抗性分离株的 序列分析并未显示出任何与抗性相关的点突变。在 DMI 表型分型的广泛分离株中，对 上游的扩增和测序导致检测到 DNA 插入，并且存在 Mona 或其他独特序列。目前，无法将这些独特序列的存在或它们在 上游的存在与 DMI 抗性基因型相关联。我们的结果表明，DMI 抗性在 2009 年至 2011 年期间在密歇根州的种群中建立，并且相对抗性水平继续增加，以至于大多数果园都存在实际抗性。此外，Mona 插入物的存在不是识别密歇根州 中 DMI 抗性分离株的标记。
