Cobweb disease on oyster culinary-medicinal mushroom (Pleurotus ostreatus) caused by the mycoparasite Cladobotryum mycophilum

In autumn 2016, symptoms of cobweb disease were observed on cultivated Pleurotus ostreatus crops in Spain. Based on morphological and genetic analyses, the causal agent of cobweb was identified as Cladobotryum mycophilum. Two cropping trials, inoculated with C. mycophilum, were set up to evaluate the pathogenicity of this causal agent of cobweb. Two different inoculation methods were used: (i) an agar plug was taken from the growing edge of a C. mycophilum isolate and placed in the centre of each hole in the block of P. ostreatus substrate (IP), and (ii) spraying each hole with a conidial suspension (ISC). In both trials, there were significant differences in disease incidence between the controls and the inoculated samples, but there were no significant differences between the two inoculation treatments. Between 75 and 87.5% of the blocks of the IP treatments and 100% of the blocks of the ISC treatments showed cobweb symptoms. Cladobotryum mycophilum was consistently re-isolated from the inoculated blocks (100%). These findings suggest that C. mycophilum can equally cause cobweb disease in A. bisporus, P. eryngii, and P. ostreatus mushroom crops.