Downy mildew, caused by the obligate oomycete Peronospora effusa (Pfs), is the most economically important disease of spinach. In recent years, numerous new races of the pathogen have overcome the resistance used in newly released cultivars. Resistance to Pfs in spinach is predominantly governed by dominant major resistance genes (RPFs) that are widely used in commercial spinach hybrid cultivars. Currently, a labor and resource-intensive inoculation test of whole plants, in a large tray format, in a temperature-controlled growth chamber and dew chamber, is employed to evaluate the resistance of spinach germplasm and to characterize races of the downy mildew pathogen. The objective of this work was to evaluate, standardize, and validate a more efficient detached leaf inoculation method to differentiate resistant and susceptible spinach genotypes and characterize Pfs races on a standardized set of spinach differential genotypes. Detached leaves and cotyledons of standard host differentials commonly used for race differentiation were placed on water agar in closed Petri dishes and inoculated by spraying the leaves with a spore suspension of Pfs inoculum. Disease incidence and severity on detached leaves and cotyledons were compared to the response of the corresponding cultivars in the standard whole-plant assay. There was a complete match between the disease reaction on whole plants and the disease reaction on detached leaves for all three races of Pfs examined. Furthermore, the obligate pathogen could infect, sporulate, and maintain pathogenicity by propagation solely on detached leaves. The detached leaf assay could facilitate advances in breeding for Pfs by evaluating resistance, pathogen race identification, and studies on epidemiology and genetics of the pathogen as the tests are less labor, resource-intensive than the whole-plant assay format, and environmental variables can be more accurately controlled.

由专性卵菌性Peronospora effusa（Pfs）引起的霜霉病是菠菜中最重要的经济疾病。近年来，许多新的病原体种族已经克服了新发布品种的抗药性。菠菜对Pfs的抗性主要由显性主要抗性基因（RPFs）广泛用于商业菠菜杂交品种。当前，在温度控制的生长室和露水室中以大托盘形式对整个植物进行劳动和资源密集的接种测试，以评估菠菜种质的抗性并表征霜霉病病原体的种族。这项工作的目的是评估，标准化和验证一种更有效的分离叶片接种方法，以区分抗性和易感菠菜基因型，并在一组标准化的菠菜差异基因型上表征Pfs种族。将通常用于种族分化的标准宿主差异的分离的叶子和子叶放在密闭培养皿中的水琼脂上，并通过在叶子上喷洒孢子悬浮液接种。Pfs接种物。在标准的全植物试验中，将叶片和子叶上的病害发生率和严重程度与相应品种的反应进行了比较。对于所检查的所有三个种族的Pfs，在整个植物上的病害反应与在离体叶子上的病害反应之间完全匹配。此外，专性病原体可以通过仅在离体的叶片上繁殖而感染，形成孢子并保持致病性。叶片分离试验可促进Pfs育种的进展 通过评估抗药性，病原体种族鉴定以及对病原体的流行病学和遗传学的研究，因为这种方法比全植物检测形式的劳动量少，资源密集，并且可以更精确地控制环境变量。