Identification, incidence and control of bacterial blotch disease in mushroom crops by management of environmental conditions

Bacterial brown blotch disease is one of the most serious bacterial diseases in cultivated mushrooms. Fluorescent pseudomonas isolated from different lesions on the caps of cultivated Agaricusbisporus were identified as strains of Pseudomonas tolaasii and the poorly described Pseudomonas “reactans”. Anaccurate identification of P. tolaasii was carried out by sequencing 16SrDNA gene. Phenotypically the isolates were heterogeneous, which further hindered their correct identification. Regarding P. “reactans”, this bacterial name is not regarded as a valid name and there is no type strain. In this work we have named as P. reactans type those isolates that induce the precipitation of tolaasin. This would suggest that we are not dealing with one species but a group of bacteria. Both, P. tolaasii and P. reactans were shown to be pathogenic in the assays performed, so the aetiology of the disease can be manifold.The incidence of blotch disease in Spanish mushroom crops was evaluated to affect up 15% of the total yield, with the highest losses detected for the second flush. The development of the disease wasassociated with high relative air humidity registered on the irrigation day closest to the harvesting of the second flush, which may lead to condensation on the caps as soon as the air temperature changesif there is no adequate ventilation. Modifying the environmental conditions by increasing the temperature prior to irrigation and moderating the manoeuvres of the drying processhelped control bacterial blotch disease.