RESUMEN
This work was carried out to isolate and identify the causal organism. Studies included also the host range of the organism. The causal organism was isolated from naturally infected stems of Dieffenbachia picta showing typical rot symptoms. All plants used for isolation were grown in the greenhouse of Faculty of Agriculture in Menia. Four isolates of motile, rod shaped, Gram-negative bacteria were isolated from soft rotted areas. The disease was induced by artificial inoculation of healthy stems of Dieffenbachia with any of these isolates. The bacterial isolates differed in their virulence. Host range studies revealed that the pathogen is able to produce soft rot on fruits or stems of eggplant, tomato, pepper, squash, potato tubers, carrot, turnip and table beet roots. Inoculated stems of chrysanthemum and potato became soft and the softened areas spread rapidly to cause wilting and death of affected plants. Stems of maize and cowpea show no symptoms and remain unaffected. Diagnostic tests and electron microscopic examination suggested that the pathogen as a new species for which the name Erwinia dieffenbachii is proposed. This is the first report on the occurrence of E. dieffenbachii in Egypt