La France disease of the cultivated mushroom Agaricus bisporus in Poland.

Presence of the virus associated with La France disease was confirmed in the mushrooms collected from different farms located in Western Poland. Double-stranded RNA (dsRNA) was isolated from the mushrooms exhibiting a wide range of the disease symptoms including premature veil opening, brown-colored mushrooms, and loss of crop yield. The presence of dsRNA molecules (M1, M2, and L3) was confirmed by RT-PCR and sequencing. Furthermore, La France isometric virus (LFIV)-like particles were observed in the mushrooms extracts in electron microscopy. The LFIV infection was found in 120 of 200 mushroom samples tested. The amount of the infected samples indicated the high occurrence of La France disease that could be a threat to the mushroom industry in Poland.