Volumetric Spore Traps Are a Viable Alternative Tool for Estimating Heterobasidion Infection Risk

Prophylactic stump treatments against the conifer root rot fungus Heterobasidion annosum s.l. should take into account the airborne inoculum density of the pathogen, in order to be economically feasible. Our objective was to test if an automatic volumetric spore trap (AVST) could be used as a sensitive alternative of passive traps for quantifying Heterobasidion airspora in forest stands. The routinely used wood disc exposure method (WDE) was implemented simultaneously with AVST in five coniferous monocultures and three near-natural stands without silvicultural management in Czechia. Air sampling took place for 24-h intervals in five months of the main sporulation period. The atmospheric concentration of H. annosum s.l. spores (cHa) was determined by qPCR with generic and species-specific primers. AVST detected more target species than WDE on 77% of sampling occasions. When comparing the relative abundance of the three European H. annosum s.l. species detected by AVST and WDE, H. parviporum and H. abietinum were found to be overrepresented on wood discs. cHa in November was significantly higher than in May and June, confirming the seasonal pattern typical for temperate Europe. For an accurate and rapid estimation of Heterobasidion primary infection risk, the usage of AVST is highly recommended.