Changes in Populations of Erwinia Carotovora in Relation to the Development of Soft Rot in Wounded Potato Tissue

Susceptibility of potato tissue to bacterial soft rot caused by Erwinia carotovora pv. carotovora (Ecc) is enhanced when inoculated tubers are incubated under conditions of low oxygen in anaerobe jars or in a mist chamber. However, Ecc populations increase and are maintained at inoculated injection and bruise sites following aerobic incubation even though soft rot does not develop. Whole tubers were inoculated with a rifampicin-resistant Ecc strain (SR 392) by injection prior to incubation in air or anaerobe jars. Additional tubers were inoculated by placing a drop of bacterial suspension at bruise sites prior to incubation in air or in the mist chamber. Populations at sites injected with low concentrations (10–500 C. F.U.) of Ecc increased when incubated aerobically and could be recovered 2 months after inoculation. After anaerobic and aerobic incubation, populations of Ecc at injection sites increased at similar rates to comparable levels. Soft rot did not develop in aerobically incubated tubers. In contrast, soft rot developed in 2–4 d at injection sites incubated in anaerobe jars. In bruise sites injected with high concentrations of Ecc (105 C.F.U.), populations of Ecc increased and high populations were recovered for more than 3 wk at 20C and for more than 2 months at 6C. Soft rot did not develop in bruise sites even after long incubation under aerobic incubation conditions.