从河南省嵩县送检的烟草茎黑腐病样本上分离获得1株腐霉菌，为明确该菌的种类及对烟草的致病力，对所得菌株进行形态学鉴定、DNA序列分析和致病性测定。结果表明，菌株菌落呈放射状型，并逐渐变为花瓣型，菌丝无隔；孢子囊球形、梨形；藏卵器球形；雄器钟状或不规则；rDNA-ITS序列测定分析，该菌序列与GenBank上登录号KC014615.1和GU133597.1等的序列同源性大于99%，鉴定为钟器腐霉(Pythium vexans de Bary)。对培育到10叶期的‘中烟100’品种接种，7天后该菌的病情指数为48，对照瓜果腐霉(P. aphanidermatum)的病情指数为62.7，表明其对‘中烟100’的致病力不及瓜果腐霉。

Pythium was isolated from tobacco stems back rot samples in Song County of Henan Province. In order to know its classification and pathogenicity to tobacco, the morphologic characters that based on microscopy technology were examined and recorded, the rDNA- ITS sequences were analyzed, the pathogenicity tests were conducted. The results showed that the colonies were actinomorphic and gradually grow into petaliform; hyphas were without separate; sporangiums were spherical or pear-shaped; archegoniums were spherical; antheridiums are bell-shaped or irregular. According to the results of the analysis of rDNAITS sequences, the sequence homology was more than 99% when it was compared with the sequence of registration number kc014615.1 and gu133597 in GenBank. Therefore, the pathogen was identified asPythium vexans de Bary. Seedings in ten leaf stage of‘Zhongyan 100’tobacco variety were inoculated withP. vexans de Bary, and the disease symptoms and the disease indexes were surveyed and recorded in the 7th day, the disease index ofPythium vexans was 48 and theP. aphanidermatum was 62.7, the results indicated that the pathogenity ofPythium vexans was less thanP. aphanidermatum.