UNRAVELLING THE VIRAL COMPLEX IN AGARICUS BISPORUS
Department of Plant Pathology, Pennsylvania State University, University Park, PA 16802, USA
Background and objectives
Research carried out during the past two decades has significantly advanced our understanding of the viral complex in commercial strains of A. bisporus. Several RNA viruses have been isolated and described, and information has begun to emerge on genome organization and pathological importance. This presentation will serve as a forum to review the status of knowledge of the Agaricus viruses, particularly as it relates to La France disease, and to address the possible direction and constraints of future virus research.
Results and conclusions
A second virus, mushroom bacilliform virus (MBV), has a genome composed of a single, linear, positive-sense ssRNA molecule (4 kb) that is packaged in a 19x50-nm bacilliform particle. MBV is the sole member of a new family of ssRNA fungal viruses known as the Barniviridae. The MBV genome has been sequenced and contains four major open reading frames, one of which encodes the capsid protein and another a putative RdRp. A survey of mushroom isolates by reverse-transcription PCR has suggested that MBV is not essential for pathogenesis, but accompanies LIV in ca 60% of the episodes of La France disease. Also, LIV and MBV are not co-dependent for replication, a conclusion based on the discovery of naturally occurring, singly infected mushroom isolates. Vesicle virus (VV), a third virus, is composed of three dsRNAs of 2.4, 5.2 and >13 kbp contained within ca 75-nm membrane vesicles. VV is widespread in commercial hybrid mushroom strains, but has not been linked to a specific phenotype; it can be detected in normal and abnormal mushrooms. Progress in gaining a precise understanding of the biological consequences of viral infection and in genetically engineering disease resistance hinges on the availability of a robust genetic transformation system for A. bisporus.