Browsing by Subject "Heterobasidion"

The root rot fungus Heterobasidion annosum is one of the worst conifer pathogens in the boreal forests. Root diseases decrease forest growth, and their abundance could increase with climate change. Disease can reduce the carbon stored into forests even more than wildfires or pest outbreaks, further impacting the climate. Widespread Heterobasidion root rot can develop within the stem of susceptible trees without external symptoms. Therefore, research on the pathogen is difficult on a large extent and its dynamics at the landscape level could be researched with models. A model may be used to understand a system better or to predict its behaviour. Random maps are neutral landscape models, and they are not always significantly different from real random landscapes, except that things shaping real landscapes, such as waterways, human activities, or topography, are missing and the focus is on map cells representing habitats, their occupancy and connectivity across the landscape. Neutral landscape models are an application of percolation theory within landscape ecology; therefore, the connectivity and randomness are important. Heterobasidion spread by sporulation at the landscape level is of interest, as the focus of research has been on the spread by root contacts. In this study, simulations made with Motti and iLand software are compared, the effects of Heterobasidion spread on the dimensional variables of trees at the landscape level are evaluated, and the effects of various maximum dispersal distances on the number of new Heterobasidion colonies and the tree volume per hectare are studied. Forest growth and management practices were simulated with the Motti software, forest dynamics were simulated with the iLand software that uses a neutral landscape model, and Heterobasidion dynamics were simulated with the BITE modelling framework that was connected to iLand for the vegetation and environmental data. Betula pendula had a trend of underestimated values of the dimensional variables except for the basal area in iLand when compared to Motti. There was no clear trend for Picea abies or Pinus sylvestris. Overall, the change in basal area was overestimated the most and height was the most underestimated variable by iLand. A single dimensional variable could have different trends during a forest growth cycle in Motti and iLand. The effect of Heterobasidion on the dimensions of trees at the landscape level was minimal. Larger maximum dispersal distances resulted in more Heterobasidion colonies than shorter distances.

Heterobasidion genus fungi are the most significant pathogens in Finland causing root rot. These fungi infect Norway spruce (Picea abies), causing wood deficit in the forest industry. Leucoanthosyanidin reductase enzyme encoding gene, PaLAR3, has been linked in to the resistance of Norway spruce against H.parviporum induced root rot infections. The alleles in this locus can be AA, AB or BB, and the enzyme production and (+)-catechin concentrations have been proven to be higher in inoculation experiments in individuals with B allele present in their PaLAR3 locus. Climate change is predicted to increase disturbances in not only on the hydrological cycles, but also on the weather conditions. The drought is predicted to increase in the Northern hemisphere, increasing the risk of pathogens to spread into new areas. Forest breeding programs aim to make the forests more profitable and productive in the future as well. By studying the genetics of Norway spruce, it is possible to add more resilient individuals into the breeding program, to tackle the climate challenges the future might hold. In this Master’s thesis the spreading of the root rot infection under drought stress was studied. The PaLAR3 alleles were determined, and the area of necrosis caused by the fungal infection was compared against the alleles, watering treatments and the fungal strain used in the inoculations. Regarding the results the alleles in an individual’s PaLAR3 locus did not have any effect on the area of the necrosis. There were no statistically significant differences between the watering treatments. The only statistically significant result was that the different fungal strains’ (Hpa1 and Hpa2) infectiveness varied between different watering treatments. This is probably due to the different routes of pathogenesis. Hpa2 strain seems to be more infective in normal watering conditions. However, considering these results the PaLAR3 gene should not be added into the forest breeding program as itself. In the future, the research should focus more on gene interactions, since also other genes (e.g., PaLAC5) have been linked in the resistance against root rot infections in Norway spruce. By studying these genes together, the solutions for the deteriorating situation of the spreading of the fungal diseases could be discovered.

In Norway spruce (Picea abies) dominated mineral soil sites, the polypore Heterobasidion parviporum often causes severe decay problems (butt rot, root rot). Not much is however known on the ability of H. parviporum to cause decay losses in peatland. The purpose of this study was to answer some fundamental question: 1) Is H. parviporum able to cause decay losses in drained mires? 2) Is there an effect of other soil microbes during saprotrophic growth of Heterobasidion on peat soil? 3) What are the potential inhibitory effects of microbes inhabiting peat soil on growth of Heterobasidion? For the decay study, wood discs (P. abies) in mesh bags were buried at the different forest sites; mineral soil and peatlands (including drained mire and undrained mire). The amount of weight loss was documented after four months. The study was repeated in vitro by autoclaving soil samples from these sites together with wood discs followed by inoculation with H. parviporum. On mineral soil, H. parviporum decayed spruce (P. abies) wood disc much more than on non-drained pristine mire. On drained (ditched) mire, no significant difference in the weight loss was observed. H. parviporum grew significantly more on the sterilized soil and decayed more wood, compared to non-sterilized soil. The results suggested that secreted metabolites in the unsterilized soil may be able to significantly suppress saprotrophic growth of H. parviporum. In the fungal growth inhibition experiment, water- and acetone-soluble substances were extracted from the soil with acetone and water. No fungal growth inhibiting substances were detected from the various peat soils or mineral soils.