Serological, Pathological, and Genetic Diversity Among Strains ofXanthomonas campestrisInfecting Crucifers

Monoclonal antibodies (MAbs) specific for strains of Xanthomonas campestris pv. campestris (Xcc) and/or X. campestris pv. armoraciae (Xca) were evaluated to determine their reliability for pathogen identification. Reactivity patterns of 1,023 bacterial isolates from crucifer leaves, seeds, weeds, and alternate crops were compared with original host symptoms; and reactivity patterns of 498 of these isolates were compared with pathogenicity tests. Six MAbs were selected that distinguished strains of Xcc and Xca from nearly all other bacteria tested. However, Xcc and Xca strains were not serologically distinguished as groups from each other, despite numerous attempts to do so. Ninety-nine percent of the Xcc and Xca strains tested reacted with one or more of the Xcc/Xca-specific MAbs. Three MAbs separated all the Xcc (and some Xca) strains into three serological groups. A subset of 12 Xcc and seven Xca strains representing the serological and pathological diversity found in these two pathovars was further evaluated by restriction fragment length polymorphism (RFLP). Strains of both pathovars were heterogeneous by RFLP, and the RFLP patterns of the seven Xca strains overlapped with patterns of the Xcc strains. However, the 12 Xcc strains formed three identifiable groups (C1, C2, and C3), which corresponded to the three serological groups (S1, S2, and S3). The type strain of the species X. campestris (Xcc528 T ) and all members of group S3/C3 caused a distinctive blight symptom that later developed into black rot. Strains in the other two Xcc groups caused typical black rot symptoms but not blight. The panel of antibodies can be used for rapid identification of Xcc and Xca pathogens in Field and seed assays