重庆烟区烟草叶斑病的诊断与鉴定

在重庆市烟草病害调查中，从彭水县润溪镇烟田发现一种未知的烟草叶斑病。为明确其病原物的分类地位，通过田间采集症状典型病害样品，经组织分离、菌株纯化并采用科赫氏法则测定其致病性，结合rDNA-ITS分子鉴定方法，对该叶斑病进行了诊断和鉴定。结果表明：该叶斑病的病斑在叶片上呈不规则形，周围有淡黄色晕圈，病部中央灰白色，且密生有黑色小点；分离物菌株psrx-1能引起健康烟株叶片发病，具有致病性；病原菌株的形态学特征表现为分生孢子座垫状、黑褐色，呈球形或半球形，分生孢子梗紧密排列、梗短小、直立，分生孢子暗褐色、球形或近球形，无隔膜，表面有颗粒状凸起或褶皱。经rDNA-ITS基因序列比对分析，将该病害鉴定为附球菌（Epicoccum sp.）引起的烟草叶斑病害，为重庆烟区首次发现的一种烟草新病害。

Diagnostic identification of a new leaf spot disease on tobacco from Chongqing tobacco-planting area

In the process of tobacco disease investigation in Chongqing, an unknown leaf spot disease on tobacco was found in Runxi Town, Pengshui County, Chongqing. To identify the taxonomy of the pathogen, typical diseased samples were collected from the affected tobacco fields. After tissue isolation, strain purification and pathogenicity determination by Koch's rule, this leaf spot disease was diagnosed and identified with rDNA-ITS molecular identification method. The results showed that the spot of the leaf disease was irregular and surrounded by a faint yellow halo, the center of the diseased part was gray white and densely covered with black spots. The strain psrx-1 isolated from the samples was pathogenic to healthy tobacco plants. The morphological characteristics of the pathogenic strains could be described as follows: the sporodochium was cushion-shaped, dark brown, spherical or hemispherical; the conidial stems were closely arranged, short and upright; the conidia were dark brown, spherical or nearly spherical without diaphragm, and the surface displayed granular bulges or wrinkles. Through rDNA-ITS gene sequence alignment analysis, this disease was identified as tobacco leaf spot disease caused by Epicoccum sp., which is a new tobacco disease reported for the first time in Chongqing tobacco-planting area.