rDNA-ITS sequence analysis of cucumber downy mildew and cucumber powdery mildew’s pathogen

Chinese. 为了应用分子特征确定黄瓜霜霉病和白粉病的病原菌种类，扩增、测定了上海地区黄瓜霜霉病菌和白粉病菌的核糖体DNA内转录间隔区（rDNA-ITS）序列，依据rDNA-ITS序列特征分析了两种病原菌种类，以及与近缘种的差异性。结果显示，黄瓜霜霉病菌的rDNA-ITS1和rDNA-ITS2长度分别为141和406 bp，rDNA-ITS1 GC含量为41.13%，rDNA-ITS2 GC含量为46.80% (闵行区株和金山区株) 或46.55% (浦东新区株)，rDNA-ITS序列在种内保守性很高，种间差异性与亲缘关系呈正相关，分子特征证实研究的黄瓜霜霉病病原菌为古巴拟霜霉菌；黄瓜白粉病菌的rDNA-ITS1和rDNA-ITS2长度分别为136 和89 bp，GC含量分别为59.56%和66.29%，rDNA-ITS序列在研究材料中保守，与瓜类单囊壳（Sphaerotheca cucurbitae）完全相同，但与形态鉴别的结果Sphaerotheca fuliginea差异高达4.5%，提示黄瓜白粉病病原菌的种类需进一步澄清和确定。

English. To determine the pathogenic species of cucumber downy mildew and cucumber powdery mildew by molecular marker, rDNA-ITS region of the cucumber downy mildew and cucumber powdery mildew’s pathogen from Shanghai was amplified and sequenced. The intra/interspecific sequence difference was analyzed by rDNA-ITS sequence. The results showed that the lengths of rDNA-ITS2 and rDNA-ITS2 were 141 bp and 406 bp, and their GC contents were 41.13% and 46.80% (sm1/sm2)/46.55% (sm3) with cucumber downy mildew’s pathogen, respectively. The rDNA-ITS sequence was highle intraspecific conservative, and interspecific difference was related with their kin relationship. Pseudoperonospora cubensis was identified as pathogen of cucumber downy mildew by molecular marker. The length of rDNA-ITS1 and rDNA-ITS2 were 136 bp and 89 bp,and GC contents were 59.56% and 66.29% with cucumber powdery mildew’s pathogen, respectively. rDNA-ITS sequence was conservative in this study, and was the same as Sphaerotheca cucurbitae. But the sequence difference between the strains of Shanghai in this study and S. fuliginea was 4.5%, which was identified by morphology. It was suggested that the pathogenic species of cucumber powdery mildew should be clarified and determined in future.