POPULATION-DYNAMICS OF ERWINIA-CAROTOVORA SUBSP ATROSEPTICA ON THE SURFACE OF INTACT AND WOUNDED SEED POTATOES DURING STORAGE

Population dynamics of Erwinia carotovora subsp. atroseptica (Eca) on the tuber surface during storage (2-4 degrees C) and pregermination, w ere studied by plating extracts of 6 mm(2) point samples on crystal vi olet pectate medium. To investigate the effect of harvest damage on Ec a survival, intact, skinned (epidermis removed), and peeled (complete peel removed) tubers from a dry (pF 3.4) and from a wet (pF 2.0) soil were inoculated either immediately after harvesting or after air dryin g for 4 h. Eca numbers on intact tuber surface decreased rapidly after inoculation, whereas at the skinned and peeled surface numbers were s ignificantly increased 2 d after harvest. Tubers peeled and inoculated with Eca were rotted by 2 d after harvest while tubers peeled and dri ed before inoculation did not rot; however, populations were significa ntly increased 2 d after harvest. For all treatments Eca numbers per p oint sample decreased to below detection limits 180 d after harvest. E xamination of 600 mm(2) surface samples of the various treatments 222 d after harvest showed that Eca populations were still present. The nu mber of tubers contaminated with colony-forming units (cfu) of Eca was significantly lower for intact surface inoculated tubers from dry soi l than for those of the other treatments. Drying for 4 h before inocul ation resulted in a significant reduction of the number of Eca cfu pos itive tubers compared to all other treatments. The ELISA OD values of the 600 mm(2) surface samples at day 222 were almost all positive and showed only a slight difference between the average of the tubers cont aining culturable Eca cells and those without culturable Eca cells.