DOUBLE-STRANDED-RNA MYCOVIRUSES IN SECTION NIGRI OF THE ASPERGILLUS GENUS

Double-stranded RNA bands were detected electrophoretically in about 7 % of natural isolates and in 13 of 51 collection strains belonging in section Nigri of the genus Aspergillus. The identity of these bands wa s proved by S1 nuclease and RNase treatment. Most of the virus-contain ing natural isolates came from Indonesia. Electron microscopic examina tion of the strains revealed the presence of virus-like particles in t he mycelia of the strains examined. All of the virus-like particles we re isometric and their size was around 30-35 nm, while some Indonesian isolates also contained virus-like particles in the size range 23-25 nm. It was possible to cure some of these strains of virus-like partic les by mutagenic treatment. The four strains tested lost their virus-l ike particles and also their 'arginine-proline leaky' phenotype and be came prototrophic. Virus transfer was possible among these four strain s by protoplast fusion. It also proved possible to transfer mycoviruse s into a more distantly related Aspergillus tubingensis strain by prol onged incubation of the polyethylene glycol treated protoplasts in osm otically stabilized medium. in spite of the finding that all Aspergill us foetidus and both Aspergillus heteromorphus strains examined contai ned double-stranded RNA segments and virus-like particles, no phenotyp es related to the presence of these VLPs have been observed so far.