Effects of temperature and heterobasidion species on the biological control efficacy of phlebiopsis gigantea

Abstract: Heterobasidion annosum sensu stricto is a damaging forest pathogen causing large economic losses to European forestry. The biological control agent Rotstop® made of Phlebiopsis gigantea oidia spores is effective on protecting freshly cut stump surfaces from H. annosum s.s. airborne infection. However, as a biological control method, Rotstop® may be sensitive to environmental factors. In this study, the effects from temperature and different Heterobasidion species on Rotstop® efficacy and Heterobasidion infection were studied both in controlled conditions (growth chamber) and in field conditions. In both situations, Rotstop® F and Rotstop® S were inoculated on freshly cut Norway spruce (Picea abies) surfaces to compete H. annosum and H. parviporum. Temperatures of the growing chambers were set at 5°C, 10°C, 15°C, 20°C and 25°C, while temperature in field condition was monitored. Colonization rate was measured and calculated on total surface, sapwood and heartwood. The identity of the originally inoculated strains was checked by somatic compatibility. The study results showed that temperature affected colonization of P. gigantea on all parts of slice; while it could affect colonization of Heterobasidion species on sapwood. P. gigantea was more sensitive to temperature shifts than Heterobasidion species.. H. parviporum was better at colonizing on Norway spruce than H. annosum in all parts of slice. Capacity of P.gigantea differed with Heterobasidion species. Both Rotstop® F and Rotstop® S could effectively reduce the colonization of Heterobasidion species, but they might have problems of protecting stump surface in cooler seasons, protecting heartwood area and competing with H. parviporum.