Browsing by Author "Mäkelä, Salla"

Heterobasidion parviporum is a major pathogenic fungus in Northern hemisphere causing root and but rot to the economically valuable conifers. The spreading of Heterobasidion to new forest sites can be controlled with several methods, but there is a strong need for new methods to control established Heterobasidion in the forest site. In Europe, another pathogenic fungus of chestnut trees, Cryphonecteria parasitica has been succesfully controlled with a fungal virus. At least 15 % of H. annosum sensu lato (Fr.) Bref isolates are infected with dsRNA viruses, however the majority of Heterobasidion viruses do not cause notable phenotypic effects on their host fungus. Viruses are known to accumulate in Heterobasdion individuals over time, but not much is known about the possible effects of multiple virus infections on the host fungus. The primary objective of this study was to investigate whether multiple virus infections of Heterobasidion viruses would cause more debilitating phenotypic effects on the host H. parviporum compared to a single virus infection. In this study, the effect of viruses on the growth rate of H. parviporum was investigated at two different temperature conditions, 6 °C and 20 °C. Secondly, the effect of Heterobasidion viruses on the competitive ability of H. parviporum against saprotrophic fungus Phlebiopsis gigantea and mycorrhizal fungi Paxillus involutus and Meliniomyces bicolor was tested on paired cultures. Additionally, Trichoderma atroviride mycelial extract was spread into the substrate and the effect of the treatment on the growth rate of virus infected H. parviporum was investigated. Thirdly, it was investigated with quantitive real time RT–PCR whether the presence of the other viruses in multiple virus infections would affect the virus (RdRp) RNA quantity of a single virus in the host mycelium. The results of the growth experiments revealed that at 20 °C HetPV13–an1 single virus infection caused radical decrease in the growth rate of H. parviporum 7R242, but multiple virus infections had no effect on the growth rate even though HetPV13–an1 was present in the multiple virus infection. At 6 °C, all the virus infections decreased the growth rate of H. parviporum 7R242 but virus HetPV13–an1 more than the other virus infections. The competitive ability of H. parviporum 7R242 against P. gigantea was reduced by virus HetPV13–an1. P. involutus was able to restrict the growth of H. parviporum 7R242 infected with multiple viruses or HetPV13–an1. M. bicolor showed slight antagonistic activity towards H. parviporum but none of the virus infections decreased the competitive ability of H. parviporum enough in order for M. bicolor to restrict the growth of H. parviporum. T. atroviride cellular exudates decreased the growth rate of all the fungal strains, but the treatment seemed to even out the effects of the viruses. The virus RdRp RNA quantity was higher in the presence of other viruses in multiple virus infections. The main conclusion of the study is that the effect of multiple virus infections on H. parviporum is not additive and multiple virus infections did not cause more debilitating effect on the host fungus compared to a single virus infection.