Taxonomy, Biological Characterization, and Fungicide Sensitivity of a New Species, Cladobotryum hypsigum, Causing Cobweb Disease in Gold Mushroom (Pholiota conissans) in China.

Pholiota conissans is an economically important edible mushroom in China; however, its production has been severely impacted by cobweb disease during the fruiting stage, leading to substantial yield losses. In this study, a fungal pathogen was identified as the causal agent of cobweb disease. The strains were isolated from infected fruiting bodies collected in November 2021 and were identified as a new species Cladobotryum hypsigum sp. nov., based on morphological characteristics and a multi-locus phylogenetic analysis of four gene regions (ITS, RPB1, RPB2, and TEF). Pathogenicity tests were conducted by inoculating healthy mushrooms with a spore suspension of representative isolates. The resulting symptoms were consistent with those observed in cultivation settings, and the same pathogen was successfully re-isolated, thus fulfilling Koch's postulates. Biological characterization indicated that the optimal conditions for mycelial growth were a temperature of 25°C and pH 5. Sucrose and yeast extract were the most suitable carbon and nitrogen sources, respectively. In vitro fungicide sensitivity assays, performed using the hyphal growth inhibition method against six common fungicides, demonstrated that Carbendazim was the most effective agent. The IC50 values for Carbendazim were 0.7742 µg/mL for the pathogen and 4.827 µg/mL for the host mushroom, indicating significant selectivity. These findings provide a scientific basis for developing effective strategies to manage cobweb disease in P. conissans cultivation.