Strains of Xanthomonas campestris pv. campestris with Atypical Pigmentation Isolated from Commercial Crucifer Seeds. A. R. Poplawsky, Plant Pathology Division, Department of Plant, Soil and Entomological Sciences, University of Idaho, Moscow 83844-2339. W. Chun, Plant Pathology Division, Department of Plant, Soil and Entomological Sciences, University of Idaho, Moscow 83844-2339. Plant Dis. 79:1021-1024. Accepted for publication 20 June 1995. Copyright 1995 The American Phytopathological Society. DOI: 10.1094/PD-79-1021.

Assays of commercial crucifer seed using a semiselective agar medium yielded three bacterial strains that were similar to the black rot pathogen except for atypical pigmentation. Cultural traits and carbon source utilization (BIOLOG) identified these strains, along with a previously isolated, nonpigmented strain, as Xanthomonas campestris. Further characterization by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of membrane proteins, monoclonal antibody typing, and host symptomatology indicated that the first three strains were X. campestris pv. campestris. Wild-type X. c. pv. campestris strains show a standard DNA hybridization pattern for the pigment-encoding region (pig). However, the three atypical strains each showed one of two different molecular rearrangements in pig, indicating multiple mutational events. Over a 4-year period, atypically pigmented X. c. pv. campestris strains occurred in 1.8% of the samples that were positive for the pathogen. Thus, in screening crucifer seed for X. c. pv. campestris strains, it is necessary to test for nonpigmented and partially pigmented strains in addition to those with typical yellow pigmentation.

Keyword(s): mutants, seedborne pathogen, xanthomonadins, yellow pigments