杨树湿心材病致病细菌的分离、鉴定和侵染途径

Pathogen isolation,identification and infection characteristics of wet-heartwood disease in poplar

采用常规的组织分离法从杨树湿心材病发病心材组织中分离到10个优势菌株,将菌株分别回接健康杨树实生苗,通过侵染症状、发病率和发病程度等测定致病性,结果发现2-16号菌株能引起典型的湿心材症状,即心材变色并腐烂。对2-16菌株形态特征、生理生化进行了分析,2-16菌株16SrDNA基因序列与胡萝卜软腐果胶杆菌胡萝卜软腐亚种(Pectobacterium carotovorumsubsp.carotovorum)NBRC 14082菌株报告的序列相似度为99%。采用Mega5.0软件以相近序列构建的进化树中,2-16菌株和NBRC 14082菌株聚在同一进化枝上。鉴定2-16号致病菌为胡萝卜软腐果胶杆菌胡萝卜软腐亚种。以温室栽培的当年生中石7杨树实生苗为接种材料,将2-16号致病菌分别通过4种方式进行侵染接种,结果表明:茎刻伤和茎注射2-16致病菌株均能引起杨树植株发病,茎注射法发病率、病斑扩散长度和发病指数均高于茎刻伤法,而叶接和灌根接种2-16致病菌株均不能使杨树感病,表明茎部伤口感染是该致病菌侵染杨树的主要途径。

Ten dominant pathogenic strains were separated from wet-heartwood pathologic tissues of poplar varieties by tissue isolation in this research.Pathogenic strains were inoculated in healthy poplar seedlings by stem injection for pathogenic identification and then the symptom,morbidity and epidemic degree of seedlings were recorded.The results showed that pathogen 2-16 strain caused evident symptom（heartwood discoloration）after injection inoculation.The morphology,physiology,biochemistry of 2-16 pathogen strain were determined.The similarity of 16 SrDNA sequence between 2-16 strains and Pectobacterium carotovorum subsp.carotovorum NBRC 14082（AB6850554）was 99%.The 2-16 strain and NBRC 14082 were clustered in the same clade in the phylogenic tree built by Mega5.0.So the 2-16 strain was classified and identified as P.carotovorum subsp.carotovorum.In order to determine the major infection path,pathogen 2-16 strain were inoculated to Zhongshi 7poplar seedlings by leaf infection,stem carving infection,stem injection and root-irrigation respectively.Both stem carving infection and stem injection with 2-16 strain caused wet-heartwood symptoms in poplar seedlings.The morbidity,length of scab and disease index were higher or longer in stem injected plants than in stem carve infected plants.There were no wet-heartwood symptoms in leaf infection and root-irrigation treatments.The results indicated that the 2-16 strain was mainly invaded by stem wound infection.