The biology and epidemiology of the cobweb disease pathogen (Cladobotryum spp.) infecting the cultivated mushroom (Agaricus bisporus)

Abstract

The UK mushroom industry, worth £170m/annum suffered an epidemic of cobweb disease during the mid 1990’s. Within 12 months this hitherto mildly problematic disease became a serious economic pest - nationwide, to the extent that businesses were threatened with closure. Cobweb disease persists to this day. A diverse collection of Cladobotryum isolates were collected from within the British mushroom industry and from other sources around the world and were compared with regards to several factors. Growth rate data, conidial characteristics, pathogenicity profiles, RAPD analysis, and mating tests all suggested that whilst variation occurred between isolates, groups of similar isolates existed. In particular, molecular analysis suggested that the majority of isolates sampled from the British mushroom industry during the epidemic were closely related. Cultural factors were investigated to establish if these affected disease expression. Disease development was found to be more closely associated to A. bisporus growth than casing characteristics such as peat type, sugar beet lime rate, and matric potential. On the basis of these findings cultural conditions were not considered likely to provide a useful means of control. In contrast, epidemiological studies provided information on which alternative control measures could be based. Cobweb pathogen conidia were shown to be liberated mainly by physical disturbance and were subsequently dispersed widely by air currents. Switching the air circulation fan off and changing disease treatment were demonstrated to reduce dissemination and prevent liberation of conidia, respectively. Both were proposed as disease control techniques. Feedback from the mushroom industry suggests these alternative control measures are already reducing levels of this disease.