Xanthomonas campestris pv. campestris (Xcc) is a seed borne pathogen that causes black rot, a destructive disease of Brassica species. Internal seed infections play a major role in disease outbreaks, as they cannot be controlled. We studied when during plant development infections of plants with Xcc can result in internally colonized seeds. In 2007 and 2008, vernalized cauliflower plants of three varieties were placed in tunnels in the Netherlands and inoculated during different stages of plant development, the 8-leaf stage, during forming of secondary stems and during flowering. At harvest time, we found a systemic infection in more than 50% of all inoculated plants, irrespective when they were inoculated. Xcc was found both in the stem base and in the secondary stems at the top. However, only in flower inoculated plants, Xcc was found in disinfected seed, indicating the risks of flower infections. Therefore, we also studies the potential role of pollinating insects in the transmission of Xcc. Flies (Calliphora vomitoria) could harbor 105 cfu per fly which could survive up to 5 days externally. Artificially inoculated flies, released eight times during blooming of cauliflower plants, resulted in relatively high percentage of internally infected seeds. Xcc was frequently detected on insects collected from a heavily blackrot diseased Brassica crop by TaqMan PCR, but was rarely isolated. The potential role of insects in the epidemiology of Xcc will be discussed
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