IN Northern Ireland black leg and tuber rot of the potato are caused by Erwinia carotovora variety â Atrosepticaâ (van Hall) Holland, but two other soft rot coliforms, namely, E. carotovora (Jones) Holland, and E. carotovora variety â Aroideaeâ (Townsend) Holland, are also involved, particularly in the tuber rotting phase of the disease. The same three organisms have also been found to bo associated with the disease in Romania¹. The isolation of soft rot Erwiniae (Pectobacteria) has recently been simplified by the introduction of selective media^2,3. These media utilize as a diagnostic characteristic the ability of the bacteria to liquefy pectate gel and therefore do not differentiate between E. carotovora, E. carotovora variety â Aroideaeâ , and E. carotovora variety â Atrosepticaâ .