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. 627, 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.

Grouping of Xanthomonas campestris pathovars by SDS-PAGE of proteins

“…campestris pv. citri has been the subject of a number of taxonomic and epidemiological studies Hartung & Civerolo, 1987Gabriel et al, 1989). This pathovar is a collective designation for xanthomonads causing different diseases of citrus and related hosts (Civerolo, 1984).…”

Genetic Diversity and Pathogenicity of Xanthomonas axonopodis Strains Inducing Citrus Canker Disease in Iran and South Korea

“…These strains could be of a new pathotype due to their dissimilarity with those of other groups and their different host ranges. Strains of pathotype B and single available D strain (Mexico) could not be differentiated by DNA fingerprinting [3,4,7,8]. It would be very worthwhile to study more strains from pathotypes D and B to further investigate this close genomic relationship.…”

“…Based on this property, restriction fragment length polymorphism (RFLP) of bacterial citrus canker strains has clearly shown that pathotypes B, C and D are clonally related but highly distinct from those of groups A and E. Furthermore these studies have revealed that strains from groups B and D are indistinguishable from each other [3,4,7,9].…”

Evaluation of Proposed Amended Names of Several Pseudomonads and Xanthomonads and Recommendations

“…We reject, for the reasons stated above, inclusion of these bacteria as pathovars of X. axonopodis (30). However, we must consider carefully the possibility that these pathovars deserve reinstatement to the species level based upon the information currently available (6,11,12,33). Van (29) did not discriminate between pvs.…”

“…phaseoli. Gabriel et al (6), using nonpairwise hybridizations of plasmid probes to electrophoresed restriction endonuclease digests of genomic DNA, detected only about 20% similarity between pv. citri and pvs.…”