Genetic diversity and virulence of Xanthomonas campestris pv. campestris isolates from Brassica napus and six Brassica oleracea crops in Serbia

The present study provides insight into the diversity of 147 Xanthomonas campestris pv. campestris (Xcc) isolates obtained from six Brassica oleracea vegetable crops (broccoli, cabbage, cauliflower, collard greens, kale, kohlrabi) and the winter oilseed rape crop Brassica napus, collected from different regions in Serbia in 2014. The XCF/XCR pathovar-specific primer set was used for fast preliminary identification. In repetitive sequence-based PCR (BOX, ERIC and REP) of all isolates, a higher level of genetic diversity was found in winter oilseed rape isolates compared to isolates from the other hosts. ERIC and REP-PCR showed the highest heterogeneity, with 10 and nine banding patterns, respectively. The REP-PCR results showed the highest correlation (70%) with those obtained with multilocus sequence analysis (MLSA), performed with 10 housekeeping genes (fusA, gap-1, gltA, gyrB1, lacF, lepA, rpoD, dnaK, fyuA and gyrB2). Three distinct phylogenetic groups of winter oilseed rape isolates were detected using MLSA. Two genes, gltA and rpoD, showed the greatest ability to identify and discriminate winter oilseed rape Xcc isolates from isolates of the other six hosts. The lepA gene exhibited specific three-nucleotide changes in sequences of some of the isolates. Results of virulence testing of 18 representative isolates showed statistically significant host-pathogen specialization for Xcc isolates from winter oilseed rape, cauliflower, kale and kohlrabi. In conclusion, oilseed rape isolates are more genetically diverse and show greater specialization to their host in comparison to the rest of the tested isolates from other brassica hosts