Abstract
Pathogenic bacteria are frequently associated with mushroom sporophores exhibiting brown blotch disease symptoms. These bacteria belong mainly to Pseudomonas tolaasii or occasionally to 'Pseudomonas reactans'. Although a group of isolates originating from some Finnish mushroom farms satisfied the two characteristic criteria for diagnosis of infection with P. tolaasii (i.e. yielding a typical brown blotch symptom on Agaricus bisporus sporophores and producing a typical white line in agar when streaked towards the 'P. reactans' LMG 5329 inducing strain), results based on numerical taxonomy, siderotyping, DNA--DNA hybridizations and 16S rDNA phylogenetic analyses supported the view that these isolates constituted a novel species within the genus Pseudomonas, Pseudomonas costantinii. The type strain is PS 3a(T) (=CFBP 5705(T)=HAMBI 2444(T)).