Inference of the phylogenetic diversity and population structure of Xanthomonas campestris affecting Brassicaceae using a multilocus sequence typing‐based approach

Abstract

Xanthomonas campestris pathovars are widely distributed throughout the globe and have a broad host range, causing severe economic losses in the food and ornamental crucifers markets. Using an approach based on multilocus sequence typing, phylogenetic diversity and population structure of a set of 75 Portuguese and other Xanthomonas campestris isolates from several cruciferous hosts were assessed. Although this population displayed a major clonal structure, neighbour‐net phylogenetic analysis highlighted the presence of recombinational events that may have driven the ecological specialization of X. campestris with different host ranges within the Brassicaceae family. A high level of genetic diversity within and among X. campestris pathovars was also revealed, through the establishment of 46 sequence types (STs). This approach provided a snapshot of the global X. campestris population structure in cruciferous host plants, correlating the existing pathovars with three distinct genetic lineages. Phylogenetic relationships between the founder genotype and remaining isolates that constitute the X. campestris pv. campestris population were further clarified using goeBURST algorithm. Identification of an intermediate link between X. campestris pv. campestris and X. campestris pv. raphani provided new insights into the mechanisms driving the differentiation of both pathovars. Wide geographic distribution of allelic variants suggests that evolution of X. campestris as a seedborne pathogen was not shaped by natural barriers. However, as Portuguese isolates encompass 26 unique STs and this country is an important centre of domestication of Brassica oleracea crops, a strong case is made for its role as a diversification reservoir, most probably through host–pathogen coevolution.

New insights into the genetic diversity of Xanthomonas campestris pv. campestris isolates from winter oilseed rape in Serbia

“…Designations ST3, ST5, ST9, and ST26 correspond to the those described by Cruz et al . (2018); ST47 corresponds to AP12 recently described by Bella et al . (2019).…”

“…campestris provided by Cruz et al . (2018). These 75 strains were obtained from different countries and included 1 strain of Xanthomonas sp., 4 strains of X .…”

“…The comparison was based on four housekeeping genes, P‐X‐ dnaK , fyuA , gyrB , and rpoD , which had been used for similar analysis by Cruz et al . (2018). Sequences of the comparative strains were retrieved from GenBank.…”

“…Allelic profiles that matched those described by Cruz et al . (2018) were allocated the same ST number designated by those authors.…”

Allelic profile of Serbian Xanthomonas campestris pv. campestris isolates from cabbage

“…Allelic profiles of the Serbian cabbage Xcc strains were determined based on sequences of four housekeeping genes (P-X-dnaK, fyuA, gyrB, and rpoD). The genetic structure and position of test strains were determined in relation to 33 Xcc strains selected to represent each of the 33 Xcc sequence types (STs) described so far by Cruz et al (2018) and Bella et al (2019). A list of strains used for comparison, hosts, and countries of their isolation are presented in Table 2.…”