[Studies on the variability of the phaseolotoxin production by Pseudomonas syringae pv. phaseolicola]

Isolation of bacteria from a field of bean plants (Phaseolus vulgaris L.) with conspicuous symptoms of halo blight disease resulted in 123 bacterial strains from which 57 were identified as Pseudomonas syringae pv. phaseolicola . At 18 degrees C the phaseolotoxin production of the isolated strains differs widely in submerse culture. Only few strains produce high amounts of phaseolotoxin being comparable with those of the reference strain 1321, while most of the strains show a low capability of phaseolotoxin production. Furthermore, we proved the stability of phaseolotoxin production of 29 strains. After one year about 50% of the strains were extremely reduced in their capability of phaseolotoxin production. We found that the reason for this reduction of toxin production is the appearance of Tox- segregants within a Tox+ clone. At 24 degrees C all strains (with one exception) show considerable lower amounts of toxin production or none at all: maximally 30% of the toxin amounts synthesized at 18 degrees C were produced. At 28 degrees C none of the isolated strains produce phaseolotoxin . The present data allow the conclusion to be drawn that in natural environments there exists a wide spread regarding the amount and stability of the phaseolotoxin production.