Abstract
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 adequate control measures and breeding strategies. The objectives of this study were to isolate and identify Xcc strains from northwestern Spain 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 Xcc isolates should be done by using the differential series of Brassica spp. genotypes or another alternative approach.
Highlights
Black rot, caused by Xanthomonas campestris pv. campestris (Xcc), is a destructive and seed-borne disease affecting Brassica crops worldwide
Black rot disease is widely distributed in northwestern Spain, little is known about the causal agent, Xcc, presence or race diversity
Other authors have included a few Xcc strains originated from Spain in their works as Vicente et al (2001), who included one strain from Spain belonging to race 4, in their study concerning the occurrence and geographical distribution of Xcc races
Summary
Black rot, caused by Xanthomonas campestris pv. campestris (Xcc), is a destructive and seed-borne disease affecting Brassica crops worldwide. Typical symptoms of the disease as chlorotic lesions and blackened veins on Brassica leaves were firstly described in Spain by Urquijo et al (1971). This finding was later confirmed by Ortega and López (1990) and Lema et al (2008), who identified and characterized Xcc strains from crops in the Mediterranean coast and northwestern Spain. In this last region, Brassica cultivation is basically made by numerous growers who trade their products in local markets. Screenings for resistance in this area have been conducted (Lema et al 2011), but no studies involving the pathogen have been accomplished until now
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