Reinstatement of Xanthomonas citri (ex Hasse) and X. phaseoli (ex Smith) to Species and Reclassification of All X. campestris pv. citri Strains

Abstract

A recent epiphytotic disease on citrus in Florida nurseries was caused by strains of Xanthomonas campestris with different host specificity and lower pathogenic capacities than those of previously described strains of X. campestris pv. citri. The new strains were classified as X. campestris pv. citri because they were isolated from rutaceous hosts and despite the fact that they caused a different disease than strains previously described in that pathovar. Restriction fragment length polymorphism analyses revealed that the Florida strains comprised a heterogeneous (E) group, interrelated with X. campestris pv. alfalfae, X. campestris pv. cyamopsidis, and X. campestris pv. dieffenbachiae. In contrast, the previously described strains of X. campestris pv. citri formed two highly distinct, homogeneous (A and B/C/D) groups. Furthermore, the strains of X. campestris pv. campestris, X. campestris pv. glycines, X. campestris pv. malvacearum, X. campestris pv. phaseoli, X. campestris pv. pisi, and X. campestris pv. vignicola tested were also distinctive and appeared to be only distantly related to one another and to all X. campestris pv. citri strains. We concluded (i) that some pathovars are sufficiently distinct from the type strain of the species X. campestris to be considered as separate species, (ii) that X. campestris pv. citri group A and X. campestris pv. phaseoli (not including X. campestris pv. phaseoli var. fuscans) represent distinctly separate subbranches of the genus and should be respectively reinstated to species as X. citri (ex Hasse) nom. rev. 3213 and X. phaseoli (ex Smith) nom. rev. G27, and (iii) that the X. campestris pv. citri B/C/D strains and the heterogeneous E strains should be respectively renamed X. campestris pv. aurantifolii pv. nov. and X. campestris pv. citrumelo pv. nov.