Characterization and variability of soft rot-causing bacteria in chinese cabbage in northeastern Brazil

Abstract

Yield of Chinese cabbage (Brassica pekinensis) may be limited by the occurrence of the soft rot caused by pectinolytic bacteria. Thirty-nine bacterial isolates associated with soft rot in Chinese cabbage, obtained from northeastern Brazil, were identified as Pectobacterium carotovorum subsp. carotovorum (Pcc) based on biochemical tests and URP-PCR. The variability of all isolates was assessed with reference to disease components, i.e. incubation period (IP), initial severity (ISEV), final severity (FSEV) and area under the disease progress curve (AUDPC), sensitivity to 12 antibiotics and the banding pattern of REP, ERIC and BOX in Rep-PCR. Based on IP, ISEV, FSEV and AUDPC, the isolates were distributed in six similarity groups after cluster analysis. There was significant correlation (P=0.05) between IP and ISEV. Based on the sensitivity to antibiotics, Pcc isolates were distributed in 14 groups. Significant correlations between sensitivity to gentamicin and IP (r = -0.41), as well as between sensitivity to clindamycin and FSEV (r = -0.45) were detected. There was high genetic variability among the 39 isolates based on the molecular markers. A total of 32 similarity groups were formed. No significant correlations were found between the linkage distances of molecular markers and either the disease components or antibiotic sensitivity. Overall, there was high variability in populations of Pcc affecting Chinese cabbage in north-eastern Brazil.