EVIDENCE FOR THE ASSOCIATION OF THE ENTERIC BACTERIUM EWINGELLA-AMERICANA WITH INTERNAL STIPE NECROSIS OF AGARICUS-BISPORUS

Internal stipe necrosis of Agaricus bisporus is recognized as an emerg ing and potentially serious disease in the UK mushroom industry. Sympt oms are visible only on harvest and appear as a variable browning reac tion in the centre of stipes, which may be accompanied by limited coll apse of the internal tissues. The hypothesis that this problem is of b acterial origin was investigated, initially by an extensive bacteriolo gical examination of affected mushrooms. The enteric bacterium Ewingel la americana was isolated from at least 93% of symptomatic mushrooms. Various strains of Pseudomonas fluorescens are also usually present in diseased mushrooms, but no single P. fluorescens biovar was consisten tly associated with the disease. Typical symptoms were reproduced foll owing infection trials with isolates of E. americana derived from dise ased mushrooms. In addition, strains recovered from diseased mushrooms following such trials were shown by RFLP studies to be identical to t hose applied, thereby confirming Koch's postulates for these strains. The possible contribution of other bacterial species to symptom develo pment is discussed.