Survival of potato-blackleg and soft-rot bacteria

Potato blackleg and soft-rot of tubers, caused by Erwinici carotovora var. carotovora and E. carotovora var. atroseptica, respectively, continue to cause mild to severe field, shipping, and storage losses of potatoes in California. An understanding of the survival capabilities of the bacteria and the factors that contribute to their spread is essential for the development of effective controls for these diseases. Previous studies have demonstrated that (1) the bacteria are seed-borne, and (2) they overwinter in the lenticels and stem-end portions of the seed tubers. Whether the bacteria can survive in soil, however, has been much more controversial, primarily because of the lack of sensitive techniques for detecting bacteria populations below 1000 cells/g of soil.