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青枯劳尔氏菌(Ralstonia solanacearum)是导致桑青枯病的病原菌.从广东省罗岗、英德蚕区桑园的感病桑树取样,采用TZC固体培养基分离纯化得到的3株青枯劳尔氏菌菌株G11-41、G12-9、G12-50的形态特征均有差异:G11-41菌株菌落小,菌落中央深红色,菌体形态为接近球形的短杆状;G12-9菌落不规则,菌落中央呈淡红色,菌体形态为短杆状;G12-50菌落呈不规则圆形,菌体形态呈长杆状.将3个分离菌株的菌液淋灌根部接种感染桑树植株,其致病性也存在明显差异:接种G 11-41菌株的植株发病率为11％,死亡率为0;接种G12-9与G12-50菌株的植株发病率和死亡率均为100％.根据Hayward分类标准进行生化型分类,3个分离株的6种碳源利用试验均呈现阳性反应,属于生化型Ⅲ.基于菌株的16S rDNA序列和内切葡聚糖酶基因(egl)序列构建的系统进化树将青枯劳尔氏菌分类为4个种群型,G11-41、G12-9、G12-50分离株同归属于种群型Ⅰ,其中;16S rDNA序列进化树上,G11-41与G12-50分离株的亲缘关系最近,分布在同一个进化小枝上;egl基因序列进化树上,强毒力分离株G12-9与G12-50分布在同一个进化小枝上,与弱毒力分离株G11-41有一定的进化距离.初步认为:在青枯劳尔氏菌的亚分类中,依据16S rDNA序列构建的系统进化树可能会更好地显示各分离株的地理来源;依据egl基因序列构建的系统进化树则可能会更好地显示出各分离株的致病性.“,”Ralstonia solanacearum is the pathogen causing mulberry bacterial wilt.Solid TZC medium was used to isolate and purify R.solanacearum samples collected from infected mulberry trees in mulberry field of Luogang and Yingde sericultural regions of Guangdong Province.The obtained 3 R.solanacearum isolates,i.e.G11-41,G12-9 and G12-50,had different morphological characteristics.The colony of G11-41 was small and center of the colony was in deep red color.Its bacteria were in near-spherical short-rod shape.The colony of G12-9 was irregular and center of the colony was in pale red color.Its bacteria were in short-rod shape.The colony of G12-50 was in irregular round form.Its bacteria were in long-rod shape.After bacterial solutions of the 3 isolates were sprinkled onto mulberry roots for disease inoculation,the 3 isolates showed obvious difference in pathogenicity.Mulberry trees inoculated with G11-41 had a morbidity rate of 11％ and a mortality rate of 0,while those inoculated with G12-9 and G12-50 had both morbidity and mortality rates of 100％.According to Hayward criteria of classification,the 3 isolates had positive reactions in all 6 carbon utilization tests,demonstrating that they belong to biochemical type Ⅲ.Phylogenetic trees constructed based on 16S rDNA and endoglucanase gene (eg/) sequences displayed that R.solanacearum can be classified into 4 phylotypes.G11-41,G12-9 and G12-50 isolates all belong to phylotype Ⅰ.In phylogenetic tree of 16S rDNA sequences,G11-41 and G12-50 have the closest genetic relationship and are located on the same evolutionary clade.In phylogenetic tree of egl gene sequences,strong virulence isolates G12-9 and G12-50 are located on the same evolutionary clade which have a certain evolutionary distance with the weak virulence isolate G11-41.It is preliminarily concluded that sub-classification of R.solanacearum based on phylogenetic tree of 16S rDNA sequences can better reflect the geographic origin of various isolates,while that based on phylogenetic tree of egl gene sequences can better reflect the pathogenicity of various isolates.