广东南瓜细菌性叶枯病及其病原鉴定

 在广东省雷州市发生一种南瓜(Cucurbita moschata)叶枯病,病株叶片边缘开始出现水渍状病斑,逐步发展成大病斑,后期病斑焦枯;在叶片上也可形成近圆形水渍状病斑,伴有黄色晕圈,后期病斑联合形成不规则大枯斑;叶柄和匍匐茎被侵染后呈水渍状腐烂。从病斑上分离到一种细菌,在KB培养基上,菌落为椭圆形,乳白色,半透明,边缘参差不齐,紫外灯照射下产生荧光反应。致病性测定结果表明,该病原细菌可侵染6个南瓜品种引起与田间症状相同的叶枯病。生理生化试验结果表明,该病原细菌与丁香假单胞丁香致病变种(Pseudomonas syringae pv. syringae)的特性一致。应用假单胞菌属特异引物Ps-for/Ps-rev和丁香假单胞丁香致病变种组群特异性引物Group III-F/Group III-R,可从该病原细菌中扩增出预期大小分别为1 018 bp和750 bp的目的片段。应用丁香致病变种syrB基因特异性引物B1/B2,可从该病原菌中扩增出预期大小为750 bp的丁香霉素基因片段。基于16S rDNA与gyrB基因序列系统进化分析均表明,南瓜叶枯病菌株与已报道的P. syringae pv. syringae菌株HS191(CP006256)亲缘关系最近,二者聚类在一起形成一个小分支。人工接种条件下,该病原细菌还可侵染西葫芦、丝瓜、茄子、番茄、菜豆、扁豆等植物。这些结果表明,引起广东省南瓜叶枯病的病原为丁香假单胞丁香致病变种(Pseudomonas syringae pv. syringae)。这是首次在中国发现丁香假单胞丁香致病变种引起南瓜叶枯病。

Identification of the pathogen of pumpkin bacterial leaf blight disease in Guangdong

A leaf blight disease on pumpkin(Cucurbita moschata)occurred in Leizhou, Guangdong. The water-soaked lesions appeared at the edge of the leaves of infected-pumpkins, and gradually formed large lesions. The nearly-circular water-soaked lesions also appeared on leaves with yellow haloes. The petioles and stolons were also infected by the pathogen and exhibited water-soaked rot. A bacterium was isolated from the diseased spots. The colonies on KB medium were elliptical, milky white, translucent with uneven edges, and produced fluorescence under ultraviolet light. Pathogenicity test showed that the bacterium could infect 6 varieties of pumpkin and cause leaf blight symptoms being similar to those in the fields. The physiological and biochemical analysis showed that characteristics of the bacterium were in accordance with Pseudomonas syringae pv. syringae. PCR amplification with Pseudomonas specific primers Ps-for/Ps-rev and P. syringae pv. syringae specific primers Group III-F/Group III-R produced the expected 1018 bp and 750 bp fragments, respectively. An expected 750 bp product encoding the syringomycin was amplified from the isolates of the bacterium with P. syringae pv. syringae syrB gene specific primers B1/B2. Both of the phylogenetic analyses based on the 16S rDNA and gyrB gene sequences showed that the bacterium isolates were very nearly related to the P. syringae pv. syringae isolate HS191 (CP006256) and they clustered in one branch. By artificial inoculation, the bacterium could also infect zucchini, loofah, eggplant, tomato, common bean and hyacinth bean. These results reveal that the pathogen of bacterial leaf blight disease on C. moschata in Guangdong is P. syringae pv. syringae. This is the first report of P. syringae pv. syringae causing bacterial leaf blight on pumpkin in China.