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Double-Stranded RNAs in Mycelial Cultures of Agaricus bisporus Affected by La France Disease. Karen Koons, Former graduate research assistant, Department of Plant Pathology, The Pennsylvania State University, University Park 16802; Beth Schlagnhaufer, and C. Peter Romaine. Research assistant, and associate professor of Plant Pathology, respectively, Department of Plant Pathology, The Pennsylvania State University, University Park 16802. Phytopathology 79:1272-1275. Accepted for publication 22 June 1989. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/Phyto-79-1272.

Diseased mycelial cultures of Agaricus bisporus derived from basidiocarps affected by La France disease contained nine major double-stranded RNA (dsRNA) segments ranging from 2.50 to 0.53 106 molecular weight (MW). The highest concentration of the dsRNAs (about 60 ng/g fresh weight of mycelium) occurred in cultures grown at 21 and 24 C compared with those grown at 16 or 30 C. Incorporation of [5, 6] 3H-uridine into the dsRNAs was first detected in diseased mycelium after 14 days of labeling and continued up to 28 days. Hybridization analysis revealed that the disease-specific dsRNAs labeled in vivo shared sequence homology with the dsRNAs isolated from symptomatic basidiocarps. Healthy mycelial cultures did not show these dsRNAs either by staining with ethidium bromide or radiolabeling. Our findings that the dsRNAs previously detected in diseased basidiocarps are also associated with and actively replicating in diseased mycelial cultures, further support their etiologic role in La France disease.

Additional keywords: common cultivated mushroom, mycovirus, X-disease.