Double-Stranded RNAs Associated with La France Disease of the Commercial Mushroom

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Abstract
Double-stranded RNA (dsRNA) analysis was used to clarify the purported viral etiology of La France disease of the commercial mushroom, Agaricus bisporus. Healthy and diseased sporophores were collected at 65 sites on commercial farms, and dsRNA patterns were compared after phenol extraction, cellulose column chromatography, gel electrophoresis, and ethidium bromide staining. DsRNA was detected in 19 of 22 diseased sporophore isolates and none of 43 healthy sporophore isolates. The presence of a characteristic dsRNA pattern correlated positively with La France disease symptoms. The dsRNA pattern consisted of 2.50, 2.05, 1.90, 1,70, 1.10, 0.89, 0.58, and 0.53 .times. 106 molecular weight (MW) segments. Variation in the disease-specific dsRNA pattern between sporophore isolates involved deletions of various dsRNA segments and additions of 4.5, 0.34, 0.33, 0.28, and 0.27 .times. 106 MW dsRNAs. Symptoms associated with the dsRNAs manifested as a reduced yield and, at some sites, as sporophores with elongated stems and small caps. The disclosed association of a characteristic dsRNA pattern with diseased sporophores provides strong circumstantial evidence for the etiologic role of specific virus(es) in La France disease.