Pathogenicity assays restrict the species Xanthomonas campestris into three pathovars and reveal nine races within X-campestris pv. campestris

The species Xanthomonas campestris (Vauterin) groups bacteria associated with cruciferous plants. In order to clarify and refine the pathovar and race structures within X. campestris, 47 representative strains of six pathovars were characterized for their pathogenicity on a large host range of Brassicaceae, including all original hosts. Three diseases were observed on tested plants: (i) black rot disease on cruciferous plants; it was proposed that all strains causing black rot on at least one cruciferous plant be grouped in the single pathovar X. c. pv. campestris; (ii) leaf spot disease caused by X. c. pv. raphani on hosts belonging to the Brassicaceae and Solanaceae; the sequenced strain 756C identified as X. c. pv. armoraciae was included in this pathovar and the existence of another leaf spot disease caused by X. c. pv. armoraciae was not supported; and (iii) bacterial blight of garden stocks caused by X. c. pv. incanae. No plants susceptible to X. c. pv. barbareae were found. Strains that did not induce any symptom on cruciferous plants tested, including their original hosts, were removed from the pathovar scheme and were named X. campestris only. Three new races were described in addition to the six races previously described within X. c. pv. campestris. The sequenced strains ATCC 33913 (CFBP 5241) and Xcc 8004 (CFBP 6650) belonged to race 3 and to race 9 (one of the new races described), respectively.