New insights into the genetic diversity ofXanthomonas campestrispv.campestrisisolates from winter oilseed rape in Serbia

Abstract

Winter oilseed rape has recently been described as a new host for the phytopathogenic bacteriumXanthomonas campestrispv.campestris(Xcc) in Serbia. In order to provide information about the genetic structure of this bacterium's population and its pathogenic features on this crop, a collection of 65 winter oilseed rape Xcc isolates obtained over a 5-year period (2014-2018) from different Serbian localities was examined. The presence of intrapathovar diversity within the tested isolates was confirmed by repetitive element PCR (rep-PCR), revealing 14, 10, and 4 different profiles for BOX, ERIC, and REP primers, respectively. A multilocus sequence typing (MLST) approach separated the isolates into seven groups on a phylogenetic tree. The PubMLST non-redundant database was used to compare sequences of four housekeeping genes from isolates with 75 strains ofXanthomonasspp. to determine nucleotide changes caused by host-pathogen coevolution. Five allelic profile combinations (ST3, ST5, ST9, ST26, and ST47) were determined, with ST47 being the most frequent. Pathogenicity and host range tests showed higher virulence of the tested isolates on winter oilseed rape than on otherBrassica oleraceahosts (broccoli, cabbage, cauliflower, collard greens, kale, and kohlrabi). The most aggressive isolates were NCPPB4679, NCPPB4680, and Xc361, belonging to genotype ST26. Fifty oilseed rape lines, cultivars, and hybrids showed susceptibility to the three Xcc isolates tested (of high, low, and moderate virulence), indicating that there was no resistance to the bacterium. The results provide significant information about diversification of Xcc isolates and their evolution toward specialization for winter oilseed rape.