Virome of the fungi associated with mushroom dry bubble disease

Dry bubble disease, attributed to the filamentous fungus Lecanicillium fungicola (Cordycipitaceae) results in huge yield losses in mushroom (Agaricus bisporus) cultivation worldwide. The possibilities for controlling the disease using commercial fungicides are highly limited, and therefore, there is an increasing demand for novel, alternative means of pest management. Our research objective was the comprehensive examination of viruses in the causal agents of dry bubble disease, which may open up an avenue for its virocontrol in the future. Out of 57 fungal isolates obtained from dry bubble-affected A. bisporus crops in various countries, 47 (82%) were confirmed by ITS (Internal Transcribed Spacer) sequence analysis as L. fungicola. In addition, different members of the genera Akanthomyces and Simplicillium (7 and 3 isolates, respectively), yet unknown to cause dry bubble symptoms, have also been detected. Cellulose column chromatography revealed the presence of double-stranded (ds) RNA in seven L. fungicola and three Akanthomyces sp. isolates, suggesting viral infection. The ten dsRNA-positive and eight randomly selected dsRNA-negative fungal strains were subjected to rRNA-depletion high-throughput RNA-sequencing analysis. The presence of seven new viruses representing four new species in the established families, Partitiviridae, Polymycoviridae, Botourmiaviridae and the narna-like virus group, and three previously established/proposed species in the families Chrysoviridae and "Mycovirgaviridae" were confirmed. The impact of the detected and identified viruses on their host fungi, and their potential applicability for virocontrol purposes will be examined in the future. This study provides the first detailed report on viruses of mushroom pathogenic fungi.