Powdery mildew caused by the obligate biotrophic fungus Podosphaera xanthii poses a serious threat to melon (Cucumis melo L.) production worldwide. Frequent occurrences of the disease in different regions of South Korea hints at the potential existence of several races which need to be identified. The races of five isolates collected from different powdery mildew affected regions were identified based on the pathogenicity tests of these isolates on eight known differential melon cultigens namely, SCNU1154, PMR 45, WMR 29, PMR 5, MR-1, PI124112, Edisto 47 and PI414723. None of the isolates have shown same disease responses to those of the known races tested in this study and in previous reports on these identical differential melon cultigens. This indicates that the tested uncharacterized isolates are new races. Among the isolates, the isolates from Hadong, Buyeo, Yeongam and Gokseong have shown same pathogenicity indicating the possibility of these isolates being one new race, for which we propose the name 'race KN1'. The isolate of Janghueng have also shown unique disease response in the tested differential melon cultigens and hence, we identified it as another new race with a proposed name 'race KN2'. Report of these new races will be helpful in taking effective control measures in prevalent regions and for future breeding programs aimed at developing varieties that are resistant to these race(s).

中文翻译：

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确定在韩国瓜中引起白粉病的两个新的Podosphaera xanthii种族。

由专活体营养性真菌引起的白粉病叉丝单囊苍耳子姿势瓜构成严重威胁（甜瓜L.）生产遍布全球。该疾病在韩国不同地区的频繁发生暗示着需要确定的几个种族的潜在存在。根据对八株已知甜瓜品种的致病性测试，鉴定了从不同白粉病影响地区收集到的五种菌株的种族，这些菌株分别为SCNU1154，PMR 45，WMR 29，PMR 5，MR-1，PI124112，Edisto 47和PI414723。这些分离株均未显示出与本研究和以前关于这些相同的甜瓜栽培种所测试的已知种族相同的疾病反应。这表明测试的未鉴定菌株是新种族。在这些菌株中，有来自河东，扶余，Yeongam和Gokseong已显示出相同的致病性，表明这些分离株可能是一个新的种族，为此我们建议使用“种族KN1”。Janghueng的分离株在经过测试的甜瓜品种中也显示出独特的疾病反应，因此，我们将其鉴定为另一个新种族，其名称为“种族KN2”。这些新种族的报告将有助于在流行地区采取有效的控制措施，并有助于旨在开发对这些种族具有抗性的品种的未来育种计划。