R. Jalkanen

Inoculation of known and potential alternate hosts with Peridermium pini and Cronartium flaccidum aeciospores

The ability of Peridermium pini and Cronartium flaccidum aeciospores and mycelium to infect known (Vincetoxicum spp., Pedicularis spp., Paeonia spp.) and potential (Melampyrum spp., Pyrola sp., Dactylorhiza sp., Solidago sp., Salix sp., Geranium sp. and Maianthemum sp.) alternate hosts was tested. None of the mycelial cultures and only 10% of the aeciospore samples produced uredinia or telia on the tested species suggesting that most aeciospores in Finland belong to the autoecious P. pini. Aeciospores from three locations in northern Finland, however, produced uredinia or telia on Vincetoxicum mongolicum, V. nigrum, V. fuscatum, Paeonia anomala, three P. officinalis cultivars, Melampyrum sylvaticum and Pedicularis palustris either in vitro or in vivo, indicating that these aeciospores belong to the heteroecious C. flaccidum, which occurs sporadically in Finland. Interestingly, the host-specificity of C. flaccidum encountered in Finland was very low (e.g. one sample produced uredinia or telia on eight species). This, added to the wide distribution of Melampyrum spp. over northern Fennoscandia, suggests that the main alternate hosts for C. flaccidum in Finland may be in Melampyrum rather than Pedicularis.

Morphological variation of Peridermium pini and Cronartium flaccidum aeciospores

Morphological variation of germ tubes originating from aeciospores of Peridermium pini and Cronartium flaccidum populations on Pinus sylvestris was investigated in rust populations from Finland, the United Kingdom and Italy. The observed morphological variation was generally higher among than between these rust populations. The variation in germ tube length of the rust samples was high over the incubation period. Peridermium pini could not be distinguished from C. flaccidum based on its germ tube morphology.

A novel badnavirus discovered from Betula sp. affected by birch leaf-roll disease

In declining birches (Betula sp.) from different European stands affected by the “birch leaf-roll disease” (BLRD) a novel virus is identified by means of RNA-Seq virome analysis. The virus represents a new member in the genus Badnavirus, family Caulimoviridae, tentatively named Birch leaf roll-associated virus (BLRaV) and it is the first badnavirus found to infect birch. Complete genome sequences (7,862–7,864 nucleotides) of three viral isolates of Finnish and German origin have been determined. The virus sequences show a typical badnavirus organization with three major open reading frames (ORFs) and a fourth potential ORF overlapping with the end of ORF3. ORFs 1-2-3 show low level of amino acid identity to the corresponding proteins encoded by other badnaviruses, reaching a maximum of 44% identity (ORF3). Grapevine vein-clearing virus appears as the closest badnavirus when considering the polymerase region. So far, we can exclude evidence for presence of endogenous BLRaV elements in the birch genome, while evidence for the episomal activity of BLRaV is provided. The viral population holds significant haplotype diversity, while co-infection by different BLRaV variants are observed in single hosts. BLRaV presence is associated with the BLRD in both silver (B. pendula) and downy birch (B. pubescens). These results challenge the earlier hypothesis of a causal role of Cherry leaf roll virus in BLRD. Further work is now needed to finally prove that BLRaV is the causal agent for the BLRD.