A double-stranded RNA mycovirus in Botrytis cinerea

Abstract

In wild-type Botrytis cinerea CVg25 strain we have detected the presence of extrachromosomal genetic elements corresponding to double-stranded RNA molecules. These genetic elements have been designated L, M 1 and M 2 with molecular sizes of 8.3, 2.0 and 1.4 kb, respectively. The visualization by electron microscopy of mycelium ultrathin sections from B. cinerea CVg25 showed the presence of isometric virus-like particles of about 40 nm in diameter. Linear sucrose gradient centrifugation of mycelium-free extracts was done to determine if the double-stranded RNAs were associated with virus-like particles. The gradient profile obtained at 260 and 280 nm revealed a major peak that was analyzed by both agarose-gel electrophoresis and electron microscopy. It was observed that only the L-double-stranded RNA molecule copurified with isometric virus-like particles. These virus-like particles had a similar morphology and size as those detected by electron microscopy in the mycelium sections. These results suggest that only the L-double-stranded RNA would be encapsidated.