Using sniffer dogs for non-invasive detection of Heterobasidion root rot from scent stimuli derived from Norway spruce trees

Sammanfattning: The fungi of Heterobasidion spp. are known to cause root and butt rot disease, and are responsible for major economic losses to forestry sector in Sweden. The fungal infection in Norway spruce (Piecea abies(L.)Karst.) is often developing over many years without visible symptoms. Existing detection methods are invasive, costly or not reliable. There is a need for a developing and implementing better methods for detecting Heterobasidion spp. infection at an early stage, preferably when the pathogen is still present in the root systems. The objective of this study was to test sniffing dogs` ability to detect the presence of the scent of an early Heterobasidion spp. infection in the spruce. A field trial was prepared with scent samples in liquid and solid form, extracted from infected spruce trees, and randomly located within experimental blocks with control substrates from healthy tree, as well as blank treatment. Seven teams of dogs and their handlers investigated blocks with five treatments each. The water extracts were applied on the ground surface, solid wood bits were buried under the ground. Test was carried on in three tours to investigate potential changes in dogs` alerts over time. The infected material was found by the dogs more often than expected by chance. Dogs correctly identified 70% of all infected samples. Combined results for infected and control treatments show 76% of true alerts. Detectability of water and solid samples changed over time. All the extracts from infected tree were detected by dogs in the first round while just 52% of infected solid material was detected. Blank samples were correctly identified in 94% of searches. Dogs and their owners who were taking part in the field trail were not professionals. Possible development of a synthetic substance mimicking the scent of infection would enable more efficient sniffer training of dogs. This study clearly states, that there is a chance for implementing the use of detection dogs as a non-invasive root rot detection method, nevertheless details regarding training aids, costs or certification need to be refined.