Rahnella aquatilis Ra39 – a bacterial antagonist against fire blight (Erwinia amylovora)
The epiphytic bacterial strain Rahnella aquatilis Ra39 was shown to reduce fire blight symptoms in field trials during 1998, 1999 and 2000. The isolate was investigated on its mode of action against Erwinia amylovora, the causal agent of the disease. The interaction between the populations of the fire blight pathogen E. amylovora strain Ea7/74 and R. aquatilis Ra39 was studied in vitro. In experiments with cocultures, a direct inhibition of Ea 7/74 by Ra39 in vitro was observed at a sucrose concentration of 0.2% but not at a concentration of 2%. Therefore competition for sucrose might be involved in the mode of action of R. aquatilis Ra39 against fire blight. Furthermore it could be shown that the lipopolysaccharide of R. aquatilis Ra39 is able to inhibit the multiplication of Xanthomonas campestris pv. begoniae, the causal agent of the Oil Spot Disease of Begonia tuberhybrida in leaves of its host plant. From the observations on this model system it was concluded that induced resistance may also play a role in antagonism of R. aquatilis Ra39 against E. amylovora.