• afforestation;
  • conifer seedlings;
  • forest nurseries;
  • ITS and DNA sequencing;
  • Phialocephala fortinii;
  • root pathogens

Fungi colonizing decayed roots of Pinus sylvestris and Picea abies seedlings were assessed by pure-culture isolation and direct sequencing of DNA extracted from roots collected from three environments: bare-root forest nurseries; afforested clear-cuts; and abandoned farmland. Pure-culture isolation from 1500 roots collected from 480 seedlings (240 of each tree species) yielded 1110 isolates which, based on mycelial morphology and ITS rDNA sequencing, were found to represent 87 distinct taxa. Direct ITS rDNA sequencing from decayed sections of 140 roots (70 of each tree species) yielded 160 sequences representing 58 taxa. Direct sequencing revealed a significantly higher fungal diversity per root segment than pure-culture isolation. Overall, a total of 131 taxa were found, 92 of which (70·2%) were identified at least to genus level. Only 14 taxa (10·7%) were detected by both methods, while 73 (55·7%) were detected exclusively by isolation and 44 (33·6%), exclusively by sequencing. The pathogens Fusarium oxysporum (25·6%) and Nectria radicicola (14·9%) were the most common isolates. In contrast, direct sequencing most frequently detected endophyte Phialocephala fortinii (33·1%) and Chalara sp. NS234A2 (10·0%). There were no significant differences in species richness between roots from the different environments, but there was a marked effect on fungal community structure. The results demonstrate that different fungi inhabit decayed roots of conifer seedlings in different environments, and that pure-culture isolation and direct sequencing are complementary methods that are both necessary for a complete description of the fungal communities colonizing diseased conifer roots.