Abstract:
Manitoba's seed potato program is based on increasing stock by stem cuttings and involves the regular testing of these cuttings for the blackleg organism, Erwinia carotovora variety atroseptica and the related soft rot organism, Erwinia carotovora variety carotovora. Testing began in the spring of 1976 and continued in 1977 and 1978. Some mother tubers were contaminated with both organisms in the first two years of testing, but in 1978, all mother tubers appeared free from infection. In addition, a survey of Manitoba's commercial stock was conducted during the fall and winter of 1977. The results of this study indicated that 59% of the sampled tubers rotted due to soft rot contamination. E. carotovora var. carotovora was recovered more frequently than E. carotovora var. atroseptica in the rotting tubers. A series of five experiments was conducted to study the ability of E. carotovora var. carotovora and E. carotovora var. atroseptica to survive in soil under controlled and natural environments. Several procedures of soil inoculation and bacterial recovery were evaluated. The results indicated that that low temperatures and association with plant debris prolonged the survival of E. carotovora in soil. Both varieties of E. carotovora remained viable in soil over winter under Manitoba climatic conditions and could possibly serve as a source of inoculum in the spring. The in vitro growth of E. carotovora was studied at temperatures of 10 C, 15 C, and 20 C. There were no significant differences in growth rate between E. carotovora var. carotovora and E. carotovora var. atroseptica at the latter two temperatures. At 10 C isolates of E. carotovora var. atroseptica grew significantly faster compared to isolates of E. carotovora var. carotovora. The greatest variation among isolates was observed at the lowest temperature.
