Impact of forest fire on occurrence of Heterobasidion annosum s.s. root rot and other wood-inhabiting fungi in roots of Pinus mugo

Abstract

Summary Forest fi res result in disturbance of wood- and soil-inhabiting fungal communities and also have an impact on the persistence of rot-causing fungi that are present in infected root systems. The aims of the present study were to (1) investigate the occurrence of the root pathogens Heterobasidion and Armillaria in root disease centres on burned and non-burned sites in Pinus mugo forest and (2) study the impact of forest fi re on the community structure of other wood-inhabiting fungi colonizing tree roots. A total of 18 root disease centres were investigated in 120-year-old plantations on sandy dunes in the Curonian Spit of western Lithuania, 14 of which were located on burned and 4 on non-burned sites. A total of 484 fungal isolates representing 16 taxa were obtained from 270 P. mugo root systems sampled at 10 – 30 cm in the soil. The two most frequently isolated fungi were Trichoderma viride and Penicillium sp. found in all disease centres and 96.7 per cent and 39.6 per cent of root systems, respectively. Heterobasidion annosum s.s. was the most commonly isolated basidiomycete found in 15 disease centres. Overall, it was isolated from 19.3 per cent of the root systems. The fungus gave growth from 42.5 per cent of root systems on non-burned and from 15.2 per cent of root systems on burned sites, and the difference was statistically signifi cant (chi-squared test; P < 0.001); thus forest fi re in disease centres seemingly had reduced occurrence of the pathogen. Nevertheless, H. annosum s.s. persisted on 11 burned sites, and on four of those fresh sporocarps were observed. Armillaria borealis was less commonly isolated (3.0 – 5.0 per cent of the root systems). Somatic incompatibility tests with 35 strains of H. annosum s.s., isolated from six (two from burned and four from non-burned) disease centres, showed genetically diverse populations of the fungus even within small and compact areas (0.01 – 0.07 ha). Fungal communities and species richness were moderately similar in burned and non-burned sites. Results of the study suggest that forest fi res on sandy soil can reduce the occurrence of H. annosum s.s. in disease centres in P. mugo plantations.