Incidence of Phlebiopsis gigantea large virus-1 in a collection of Phlebiopsis gigantea isolates.

Eighty six Phlebiopsis gigantea isolates from at least 9 different tree species from various locations in 12 different European countries and North America were screened for the presence of large molecular weight dsRNA >10 kbp in size. In 7 isolates, which contained large dsRNAs, the presence of Phlebiopsis gigantea large virus-1 (PgLV-1) was suggested following the sequencing of the RT-PCR amplicons generated with PgLV-1 specific oligonucleotide primers which also revealed little genetic diversity between the virus isolates.

Incidence of endornaviruses in Phytophthora taxon douglasfir and Phytophthora ramorum.

In this investigation, we show that four Phytophthora taxon douglasfir isolates from the USA, irrespective of their geographical location or host plant, and 20% of a representative cohort of Phytophthora ramorum isolates contain endornavirus dsRNAs. Three endornavirus-specific RT-PCR amplicons were generated by RT-PCR using dsRNA isolated from the four Phytophthora taxon douglasfir isolates and one representative Phytophthora ramorum isolate as template with oligonucleotide primers designed from the sequence of Phytophthora endornavirus 1. The amplified segments showed a very high degree of sequence similarity suggesting that the virus has gone through a population bottleneck during its emergence.

Molecular characterisation of two novel double-stranded RNA elements from Phlebiopsis gigantea.

The incomplete sequences of two large, 10-12 kbp, double-stranded RNAs (dsRNAs) found in the TW-2 isolate of the saprophytic fungus, Phlebiopsis gigantea (Pg) are reported. Both PgV-TW2 dsRNA1 and dsRNA2 potentially encode fusion proteins which are apparently expressed by a translational frameshifting mechanism. The C-terminal region of both predicted proteins was 21% identical and contained the eight motifs conserved in RNA-dependent RNA polymerases of dsRNA mycoviruses and had highest similarity with members of the family Totiviridae, but possibly do not form virions. The remainder of the N-terminal protein sequences predicted from the PgV-TW2 dsRNA1 and dsRNA2 sequences and the 3'-terminal nucleotide sequences of both dsRNAs had no homology with one another or any sequence in the database suggesting that individually both may be members of novel families of mycoviruses.