引起广西桑树“褐枯”的病原菌及致病机制研究

Identification of the Pathogen of Mulberry Bacterial Wilt in Guangxi and Its Pathogenic Mechanism

对广西地区的桑树发病初期叶片褐枯情况进行调查,通过收集桑树病株并进行分离。结果表明,得到优势菌株42株,各菌株形态基本一致。对分离到的菌株进行16S rDNA序列鉴定,比对后发现所有菌株序列均与劳尔氏青枯菌Ralstonia solanacearum(RS)相似度达99%,生化型分析结果显示主要为生化Ⅰ型。随机选择10个菌株进行致病力实验,结果表明,各菌株均具有致病性,部分菌株致病率达90%以上。其后利用扫描电镜观察青枯菌侵染桑苗过程,发现侵染后期桑根木质部导管内聚集大量菌体,堵塞整个导管。上述结果表明:广西地区桑树"褐枯"症状病害属于桑树青枯病,病原菌为劳尔氏青枯菌RS,其致病机制是通过在桑根木质部导管内大量定殖,堵塞导管阻止水分运输,最终导致植株枯萎死亡。

In recent years,a preliminary investigation showed that some new symptoms of mulberry bacterial wilt appeared in Guangxi,showing leaf wilt with brown color.In this study,we investigated epidemic area of mulberry bacterial wilt in Guangxi.Forty two predominant strains were obtained by collecting disease plants and isolating on the TTC medium,and the morphology of all strain was consistent.The result of 16S rDNA sequence comparison among the isolated 42 strains showed that the similarity of all strains on nucleotide level with Ralstonia solanacearum（RS）was up to 99％.Biochemical type analysis indicated the strains were mainly biochemical type Ⅰ.Pathogenicity test of 10 randomly selected strains showed that all strains were pathogenic,and pathogenic rate of several strains was more than 90％.Then,using scanning electron microscope,we observed the process of RS infecting mulberry seedlings.We found that a lot of bacteria thallus gathered in xylem vessels of mulberry root in later infection stage,blocking the whole vessels,All the results above showed that the pathogenic bacteria of mulberry bacterial wilt in Guangxi was RS.The pathogenic mechanism of RS was massive colonization in xylem vessels of mulberry root,blocking the whole vessels and preventing water transport,and eventually leading to plant death.