Shi Ainong, Mmbaga Margaret T
Tennessee State University, Otis A. Floyd Nursery Research Center, 472 Cadillac Lane, McMinnville 37110.
Plant Dis. 2006 Aug;90(8):1098-1101. doi: 10.1094/PD-90-1098.
The fungus Erysiphe lagerstroemiae is commonly known as the powdery mildew pathogen in crape myrtle (Lagerstroemiae indica) in the United States, and Erysiphe australiana is the powdery mildew pathogen reported in Japan, China, and Australia. The teleomorph often used to identify powdery mildew fungi rarely develops in crape myrtle, and in our observations, ascocarps never formed. Our study showed that the crape myrtle pathogen overwintered as mycelia on dormant buds. The internal transcribed spacer (ITS) regions of rDNA and the intervening 5.8S rRNA gene were amplified using standard polymerase chain reaction (PCR) protocols and the universal primer pairs ITS1 and ITS4. PCR products were analyzed by electrophoresis in a 1.5% agarose gel and sequenced, and the ITS PCR product was 666 bp from ITS1/ITS4 and 704 bp from ITS1-F/ITS4. BLAST analysis of the sequence of the PCR products showed identical similarity with E. australiana reported in Japan, China, and Australia. Comparison of ITS sequences with information in the GenBank on other powdery mildew fungi showed a closest alignment (93% similarity) to Erysiphe juglandis that infects walnut. Specific primers for E. australiana were developed and evaluated for use as diagnostic tools. Out of 12 specific primer pairs evaluated, four primer pairs and four double primer pairs were highly specific to E. australiana and did not amplify Erysiphe pulchra of dogwood, Erysiphe syringae of common lilac, Erysiphe circinata of maple, or Phyllactinia guttata of oak. The E. australiana-specific primers amplified 16 samples of crape myrtle powdery mildew collected from diverse locations in mid-Tennessee. These results clearly showed that the crape myrtle powdery mildew in mid-Tennessee was caused by E. australiana. Specific primers reported in this article provide a diagnostic tool and may be used to confirm the identity of crape myrtle powdery mildew pathogen in other areas in the United States and wherever the disease occurs.
紫薇白粉菌在美国通常被认为是紫薇（Lagerstroemiae indica）上的白粉病病原菌，而澳洲白粉菌是在日本、中国和澳大利亚报道的紫薇白粉病病原菌。常用于鉴定白粉病真菌的有性型在紫薇中很少发育，在我们的观察中，子囊果从未形成。我们的研究表明，紫薇病原菌以菌丝体在休眠芽上过冬。使用标准聚合酶链反应（PCR）方案和通用引物对ITS1和ITS4扩增核糖体DNA的内部转录间隔区（ITS）区域以及居间的5.8S rRNA基因。PCR产物在1.5%琼脂糖凝胶中进行电泳分析并测序，ITS PCR产物从ITS1/ITS4扩增得到的为666 bp，从ITS1-F/ITS4扩增得到的为704 bp。对PCR产物序列进行的BLAST分析显示，与在日本、中国和澳大利亚报道的澳洲白粉菌具有相同的相似性。将ITS序列与GenBank中其他白粉病真菌的信息进行比较，发现与感染核桃的胡桃白粉菌的比对最为接近（相似性为93%）。开发并评估了用于澳洲白粉菌的特异性引物作为诊断工具。在评估的12对特异性引物对中，4对引物对和4对双重引物对对澳洲白粉菌具有高度特异性，不会扩增山茱萸的美丽白粉菌、紫丁香的丁香白粉菌、枫树的圆形白粉菌或橡树的斑点叉丝壳。澳洲白粉菌特异性引物扩增了从田纳西州中部不同地点采集的16份紫薇白粉病样本。这些结果清楚地表明，田纳西州中部的紫薇白粉病是由澳洲白粉菌引起的。本文报道的特异性引物提供了一种诊断工具，可用于确认美国其他地区以及该病发生地的紫薇白粉病病原菌的身份。
