HYBRIDIZATION ANALYSIS OF THE SINGLE-STRANDED RNA BACILLIFORM VIRUS ASSOCIATED WITH LA FRANCE DISEASE OF AGARICUS-BISPORUS

We investigated the relationship between the 19- x 50-nm single-stranded RNA (ssRNA) mushroom bacilliform virus (MBV) and the double-stranded RNAs (dsRNAs) associated with La France disease of Agaricus bisporus. Agarose gel electrophoresis under formaldehyde-denaturing conditions revealed that the MBV genome was composed of a single RNA molecule of 4.4 kb. In northern analyses, a 1.4-kb cloned complementary DNA (cDNA) to MBV RNA hybridized to the full-length genomic RNA in purified virus preparations and total RNA fractions from diseased mushrooms. A minor 1.8-kb RNA, presumably a subgenomic component, also was detected in diseased tissues. No cross hybridization occurred between this MBV cDNA clone and total RNA of healthy mushrooms. When we used either the cDNA or a combination of the nine La France disease-related dsRNAs (0.8 to 3.8 kb) as a hybridization probe, no sequence homology existed between MBV RNA and the dsRNAs found in diseased as well as healthy tissues. Our findings are consistent with the hypothesis that a viral complex involving an ssRNA virus and an unrelated dsRNA virus(es) plays a role in the etiology of La France disease.