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Pathogenic fungi can survive and develop in living plants, often causing diseases in the host. Some theories speculate that pathogenic ophiostomatoid fungi provide benefits to its vectorsbark beetlesby overcoming the tree's defence mechanisms. This study reports the results of an experiment in south-eastern Europe in which mature and seedling Norway spruce trees were artificially inoculated with various ophiostomatoid fungi. The aim of the experiment was to determine the relative virulence of ophiostomatoid fungi by assessing the ability of the fungi to stimulate host tree defence mechanisms through inoculation experiments. Experiments were performed by inoculation of Picea abies in seedling and mature trees. The following fungi were used in low-density and seedling inoculations: Ophiostoma ainoae, O. brunneo-ciliatum, Grosmannia cucullata and an unidentified Leptographium sp., O. bicolor, O. fuscum, O. piceae, G. penicillata and G. piceiperda. Endoconidiophora polonica was used in mass and seedling inoculations. Various characteristics such as host vitality, blue stain, lesion and resin outflow were measured before and after the trees were felled. E. polonica caused blue stain, induced large lesions and killed some of the mature trees and seedlings, confirming earlier reports that it is a strong wound pathogen. Only E. polonica, Leptographium sp. and O. ainoae caused blue stains in the sapwood of inoculated seedlings. In low-density inoculations, G. piceiperda induced intense necrosis and had higher values for all the characteristics monitored. Some of the other ophiostomatoid fungi showed a moderate level of pathogenicity. Fungi with the capacity to stimulate a host defence mechanism could play a role in the establishment of bark beetle populations.

SummaryThe small spruce bark beetle Ips amitinus is predominantly found in the spruce forests in mountainous areas of Central Europe. Its most important host trees are Norway spruce (Picea abies) and Scots pine (Pinus sylvestris). Under favourable weather and trophic conditions, this bark beetle can become dangerous, particularly for younger trees and plantations. The climate changes that we face today can be favourable to the species, which had not been economically important in the past but is currently causing forest damage. Information about the ecological/biological characteristics of I. amitinus in the literature is rare, especially for bark beetle-fungi associations; though bark beetle (Coleoptera: Scolytinae) species are known to be associated with variety of fungi. We investigated the factors affecting the associations of ophiostomatoid fungi with I. amitinus on Norway spruce. Material for this study was collected in the year 2010 near Dravograd, in north Slovenia, where Norway spruce trees were felled during the winter windthrow. Four hundred and forty-two samples (bark beetles and infested samples from wood discs, from two trees at 0.5 m, 6 m and 15 meters above the stump) were taken for ophiostomatoid fungi investigation. Isolation yielded a total of 625 isolates. Ophiostomatoid fungi were the most numerously represented group. Identified fungal isolates belonged to ten species. The most commonly found fungal associate was Ophiostoma brunneo-ciliatum, followed by Grosmannia penicillata, Ophiostoma bicolor, Ceratocystiopsis minuta, Grosmannia piceiperda, Endoconidiophora polonica, Ophiostoma piceae, Ophiostoma fuscum, Grosmannia cucullata, Graphium fimbriisporum. The association with O. fuscum, G. cucullata and G. fimbriisporum have not been demonstrated previously. The differences in distribution of fungi over different beetle life stages (adults, larvae, pupae) and infested wood were investigated.