Detection of Xanthomonas campestris pv. campestris using Real-time PCR
There is much about Xcc infection that is unknown, although infected seed is known to be a major source of infection and plant-to-plant spread can be rapid under certain conditions. The warm humid atmosphere of plant raising houses is ideal for the spread of Xcc, but the bacteria can be present at a pre-symptomatic level, leading to infected transplants being planted out in the field. Symptom development later in the growing season can make produce unsuitable for marketing and cause considerable economic loss.
As PCR can detect DNA from dead as well as live bacteria, we developed methods that involved an initial culture phase, so that only live bacteria would register a positive result. Seed hygiene treatments that kill bacteria could leave behind DNA that would result in a false positive if tested directly.
The PCR diagnostic test has the same level of sensitivity of detecting low level infection in seed samples as the traditional pathology test, and saves 2-3 weeks of time by avoiding the need to identify visually symptom development in inoculated plants. Xcc was also detected in plants grown on infected sites, but without visible symptoms. This offers the potential of a method for identifying pre-symptomatic infection in plants, although methods of sampling have not been worked out and pose logistical difficulties.
The financial support of the Frank Horne Memorial Fund is gratefully acknowledged.