ANALYSIS OF XANTHOMONAS-CAMPESTRIS PV CITRI AND X-C-CITRUMELO WITH MONOCLONAL-ANTIBODIES

A monoclonal antibody (MAb), designated A1, reacted with lipopolysaccharide (LPS) epitopes of all tested strains of Xanthomonas campestris pv. citri isolated from the Asiatic form of citrus bacterial canker (CBC-A), with X. campestris strains pathogenic on ti (Cordyline terminalis), and with some Florida citrus nursery strains associated with citrus bacterial spot (CBS) disease. The A1 MAb did not react with strains associated with other forms of citrus canker (B, C, or D). Except for weak reactions with X. c. manihotis, MAb A1 did not react with 130 other Xanthomonas pathovars and species or with 89 strains of other genera. In contrast, the titers of a rabbit-anti-CBC-A antiserum with several other X. campestris pathovars were as high as titers with some CBC-A strains. A second MAb, A2, reacted only with a flagellar epitope associated with CP1 bacteriophage-sensitive CBC-A strains. The CBC-B strains appeared to be antigenically heterogenous, because no MAb was produced that reacted with all CBC-B strains; however, the CBC-B strains were grouped by reactions to three MAbs specific for LPS epitopes. One CBC-B MAb, B2, indicated a close antigenic relationship between strains in groups B, C, and D. Another MAb, C1, specific for CBC-C strain XC70 reacted with a heat-sensitive epitope associated with a molecule partially sensitive to proteolytic enzymes. MAbs (T1 and T2) specific for weakly virulent strains isolated in Mexico from Citrus aurantifolia (Mexican lime) did not react with any other strains from citrus. CBS strains from Florida were serologically heterogeneous but distinct from strains associated with CBC. Most of the strongly aggressive CBS strains reacted with a MAb (CBS1) generated to a strongly aggressive strain, whereas most moderately and weakly aggressive strains reacted with MAb Xct generated to a X. campestris pathogen of ti. Moderately to weakly aggressive CBS strains reacted with MAb A1, but those strains also reacted with MAb Xct, whereas CBC-A strains did not. The LPS banding patterns of CBC-A strains were similar to each other, with major bands at an average M(r) of 80,000, and were distinguished from the LPS patterns of A1-positive CBS, ti, and X. c. manihotis strains (major bands at an average M(r) of 60,000).