Identification of cold-tolerant Pseudomonas viridiflava and P-marginalis causing severe carrot postharvest bacterial soft rot during refrigerated export from New Zealand

In 1999, New Zealand carrots (Daucus carota) exported to the Middle East incurred substantial damage due to bacterial soft rot that resulted in major financial loss to farmers. A modified carrot tissue bioassay was developed under standard conditions to provide an economical and rapid means of monitoring export carrots for bacteria able to cause severe bacterial soft rot. Using this bioassay, two bacterial isolates causing severe degradation were detected and subsequently identified as Pseudomonas viridiflava (designated NZCX09) and P. marginalis (NZCX27), using the Biolog system and 16S rRNA phylogenetic analysis. Investigation of disease epidemiology of NZCX09 and NZCX27 at low temperatures showed that tissue degradation occurred at temperatures approaching (OC)-C-o. These findings emphasize the importance of postharvest sanitization, and the efficacy of refrigeration methods used in controlling soft rots in carrots stored over time.