The interaction of the soft rot bacterium Pseudomonas gladioli pv. agaricicola with Japanese cultivated mushrooms

Abstract

The mushroom soft rot bacterium Pseudomonas gladioli pv. agaricicola was observed to cause pitting when inoculated onto tissues of several commercially important Japanese cultivated mushrooms. Scanning electron microscope studies demonstrated the sequential removal of hyphal wall layers, thereby exposing the chitin skeletal matrix, which in turn was degraded. A second type of damage typified by collapsed, shriveled, and in some cases lysed hyphal cells was also observed. Culture plate assays revealed that Pseudomonas gladioli pv. agaricicola produces chitinase and this, coupled with earlier evidence of a β-glucanase enzyme, accounted for the degradative ability of the pathogen. The gelatinous coating on the Pholiota nameko sporocarp appeared to confer resistance to Pseudomonas gladioli pv. agaricicola attack. Petri dish coincubations with several cultivated mushroom species indicated the ability of Pseudomonas gladioli pv. agaricicola to inhibit mycelial growth over a large distance and suggested the presence of a toxin or toxins. Owing to its wide host range, Pseudomonas gladioli pv. agaricicola is considered as a potential threat, not only to the mushroom industry in Japan but also to the mushroom industry in other tropical/subtropical countries.Key words: chitinase, disease, Pseudomonas gladioli pv. agaricicola, soft rot, toxin.