Abstract: The experiments conducted on 3 isolates of P.solanacearum and 7 Casurina clones revealed that the adsorption of bacterial isolates to the host root surfaces differed significantly, a negative correlation between the adsorption amount and the pathogenicity existed; The propagation of 3 isolates within the roots also varied greatly, and a strongly positive correlation existed between the propagation amount and pathogenicity. The pretreated Casuarina ramets with LPS sharply reduced the adsorption of subsequently inoculated bacteria by 58.5% 97.3%, but EPS pretreated ramets did not show any apparent change. The bactcrial cells free of both EPS and LPS lost their adsorption amount by 63.3% 74.2%in comparison to the intact bacteria. However, the EPS free only bacteria slightly increased their adsorption up to 19.1%. Electrophoresis pattern of 3 isolates through SDS PAGE also showed difference with a special Rf=0.35 band occurred for the most virulent isolate 601B. It is concluded that the pathogenicity of P. solanaearum to Casuarina is associated with its adsorption amount on the host root surfaces and especially the rapid propagation capacity inside the roots. LPS plays a role of bacterial cognon in the recognition between the pathogen and host while EPS covers or inhibites this process of LPS. Both LPS and EPS are all important factors that affect the pathogenicity of P. solanacearum.