Multiplication of Pseudomonas syringae pv. phaseolicola 'in planta': II. Characterization of Susceptible and Resistant Reactions by Light and Electron Microscopy Compared with Bacterial Countings

In the compatible combination of the halo blight disease of bean Pseudomonas phaseolicola was able to colonize large areas of the intercellular space of leaves, such that these confluent water congested areas became visible as water-soaked spots. Most of the plant cell walls in the infected region maintained their normal shape, even when the cytoplasm had collapsed. Some inward bending of plant cell walls preceded their rather slow degradation and final replacement by bacterial masses. Neighbouring plant cells appeared to be metabolically active. In resistant leaves no indications of active bacterial attachment or encapsulation could be observed. However, bacteria appeared to be more densely packed in resistant leaves, and relatively more plant cells completely collapsed as compared with susceptible leaves. From 8-14 days after inoculation, the bacterial concentration did not change much in susceptible or resistant leaves, indicating the absence of bactericidal components. Even Pseudomonas pisi showed some multiplication in bean leaves (immune reaction), but its growth stopped earlier than that of P. phaseolicola in the resistant cultivars, probably due to a different mechanism of resistance. Although less bacteria were determined in the intercellular washing fluid (IF) compared with leaf homogenates, the high bacterial concentrations in the IF supported our observation that an effective encapsulation of bacteria in resistant leaves did not occur. U.S. Copyright Clearance Center Code Sutement: 0031-9481/85/1303-0200$02.50/0 201 Multiplication of Pseudomonas syringae pv. phaseolicola "in planta"