Morphological and serological characterization of bacterial isolates from greening/dieback diseased citrus

The morphological and serological characteristics of bacterial isolates from plants infected with African greening, Reunion greening and Taiwan likubin were investigated. Isolates from Australian citrus dieback affected trees and resembling the putative greening isolates, were also included. Although predominantly long thin rods, the bacterial cells were morphologically variabile in both liquid and plate cultures at 25°C and 35°C. "Round forms" developed with age and nutrient limitations. Based on colony morphology and pigmentation, the isolates were categorized into two groups - Groups 1 and 2. Whole cell protein patterns were obtained by SDS-PAGE. Patterns of the Group 1 isolates, which were conserved with growth, were similar to one another and different from the patterns of the Group 2 isolates. In an attempt to establish a bacterial detection probe, antisera were raised against the Group 1 isolates. These sera specifically reacted with all the members of this group in slot-blot immunoassays. Using the sera in western blots, characteristic serological reaction patterns were associated with the Group 1 and Group 2 isolates. Both greening-affected and dieback-affected field samples reacted specifically with the antisera in slot-blot immunoassays. A monospecific polyclonal antiserum was also raised against a 38K - 40K protein band in western blots of the Group 1 isolates. The reaction of antigenic bands in western blots of preparations of tissue from affected trees can be achieved although the techniques involved need to be refined. Metabolically, the Group 1 isolates are somewhat related to Clavibacter michioanense subsp. michiganense. However, the protein pattern and western blot results did not support this. A Clavibacter sp. was isolated from Australian citrus dieback affected trees. A Group 1 isolate was also obtained from Australian citrus dieback affected trees.