Complexity of virus-like double-stranded RNA elements in a diseased isolate of the Dutch elm disease fungus, Ophiostoma novo-ulmi

High resolution polyacrylamide gel electrophoresis has shown that a diseased isolate of the Dutch elm disease fungus, Ophiostoma novo-ulmi, Log1/3-8d(2) (Ld), contains 12 virus-like double-stranded (ds) RNA segments instead of the 10 segments previously reported. DsRNAs 1 and 3 were each separated into two segments, designated dsRNA-1a, dsRNA-1b, dsRNA-3a and dsRNA-3b, respectively. The relative mobilities of dsRNAs 3a and 3b were reversed when electrophoresed in 4 and 8% gels, indicating that structure as well as size can contribute to electrophoretic mobility. Analysis of the dsRNA profiles of healthy isolate W2tol1 (the progenitor of Ld), and healthy single-conidial isolates derived from Ld, showed that dsRNAs 1a, 1b, 3a and 3b were not the cause of the Ld diseased phenotype. Two single conidial isolates were obtained which contained only dsRNA-6 which therefore replicates autonomously. Overall the results indicated that the 12 Ld dsRNAs are comprised of several independent replicons. The single-stranded form of dsRNA-10, which potentially has a high level of base-pairing, was shown to fractionate with the dsRNA.