Transmission of Xanthomonas campestris pv. campestris in Seed Production Crops of Cauliflower

In 2011, two polytunnel greenhouse experiments were conducted on seed production farms, one under conventional conditions in the South-West (Rilland) and the other under organic conditions in the East (Voorst) of the Netherlands, to study transmission routes of Xanthomonas campestris pv. campestris (Xcc), that can result in seed infections of cauliflower plants (Brassica oleracea var. botrytis). Each experiment consisted of three plots. Before head formation, plants in the two outside plots were spray-inoculated with either Xcc strain IPO 3076 or IPO 3078, and plants in the central plot were sprayed with water. A colony of honeybees (Apis mellifera) was placed in each tunnel to provide pollination. At Rilland, incidences of black rot were low, and seed infections were not detected in a plating assay, although peduncles were infected in a high percentage of the plants. At Voorst, black rot symptoms developed in almost all Xcc-inoculated plants, resulting in plant losses. The incidence of plants with infected seeds in the plot inoculated with Xcc IPO 3076 was higher than in the two other plots. Identification of Xcc isolates by BOX-PCR revealed that Xcc IPO 3076 was transmitted to the other plots of the experiment. Xcc IPO 3078, however, was only recovered from plants inoculated with this strain. The routes of seed infection for Xcc and then transmission of the pathogen are discussed.