Evaluation of Phlebiopsis gigantea and Pseudomonas spp. for biocontrol of Heterobasidion spp. in Norway spruce

Abstract: Root rot caused by the fungal pathogen Heterobasidion spp. is one of the most spread and devastating conifer diseases in the Northern Hemisphere. There is increasing interest from the forestry sector in new biological agents and means of control for Heterobasidion spp., as root rot becomes an economically more important issue. More consistent and effective genotypes of P. gigantea isolates would benefit the forest industry as well as reduce ecological risks connected with using just one isolate for treatment of conifer stumps locally. Therefore, the aim of this study was to examine new biological protection agents on Norway spruce wood that could potentially be used commercially for stump protection against Heterobasidion spp. The competitive ability against H. parviporum of ten different isolates of P. gigantea, including Rotstop S isolate and biological treatment Ox 24, containing a Pseudomonas spp. bacteria, were tested in laboratory conditions. In addition a small field study comparing Ox 24 and Rotstop S was evaluated. Results of the current study revealed that P. gigantea isolate S2384_2_VI is significantly (p<0,05) superior to other 9 isolates by means of average growth rate per day on top of wood heavily infected by H. parviporum. Rotstop S together with PG342 isolate had the fastest performance of growth in the first two days of juxtaposition with H. parviporum. Wood colonized by Pseudomonas spp. bacteria in vitro is resistant to H. parviporum even after 25 days of close contact. Breeding between the best isolates found in this study could be introduced in order to produce P. gigantea progenies that have higher antagonistic and biological control ability. Pseudomonas spp. showed remarkable results in resistance for H. parviporum in vitro and demonstrated apparent ability to protect stumps from primary infection with Heterobasidion spp. when compared to other treatment methods, yet it was only a pilot study of small scale. Therefore Pseudomonas spp. bacteria should be monitored in full scale field experiments before it can be considered as a potential alternative to P. gigantea in terms of biological stump control.