Discrimination of Xanthomonas campestris pv. campestris races among strains from northwestern Spain by Brassica spp. genotypes and rep-PCR

Black rot, caused by Xanthomonas campestris pv. campestris (Xcc), is a severe seedborne disease of Brassica crops around the world. Nine races are recognized, being races 1 and 4 the most aggressive and widespread. The identification of Xcc races affecting Brassica crops in a target area is necessary to establish the adequate control measures and breeding strategies. The objectives of this study were to isolate and identify Xcc strains from northwestern Spain Brassica crops, by using semi-selective medium and pathogenicity tests, determine the existing races of Xcc in this area by differential series of Brassica spp., and evaluate the use of repetitive DNA polymerase chain reaction-based fingerprinting (rep-PCR) to differentiate among the nine existing Xcc races. Seventy five isolates recovered from infected fields were identified as Xcc. Race-typing tests determined the presence of the following seven pathogen races: 1, 4, 5, 6, 7, 8 and 9. Race 4 was the most frequent in Brassica oleracea and race 6 in Brassica rapa crops, therefore breeding should be focussed in obtaining resistant varieties to both races. Cluster analysis derived from the combined fingerprints showed four groups, but no clear relationship to race, crop or geographical origin was found. Rep-PCR analysis was found not to be a reliable method to discriminate among Xcc races, therefore race typing of new Xcc isolates from other fields should be done by using the differential series of Brassica spp. genotypes or another alternative approach.