Effects of the use of biocontrol agent (Phlebiopsis gigantea) on fungal communities on the surface of Picea abies stumps

Abstract

One of the main objectives of sustainable forestry policies is to phase out, if possible, the use of chemical agents in forestry. The saprotrophic fungus Phlebiopsis gigantea has for several years been used as a biocontrol agent against the pathogen Heterobasidion annosum sensu lato. This pathogen is the major cause of root rot disease in conifers that results in economic losses estimated at 50 million euros to Finnish forestry industry annually. A major problem is that, although the effectiveness of P. gigantea as a bio-control agent has empirically been shown, the long term biological effect of this fungus on conifer trees as well as on other wood microflora has not been empirically proven. We investigated the impact of P. gigantea treatment on stump mycobiota using 454-pyrosequencing approach as this has not done before. Samples from forest sites pre-treated with P. gigantea for 1, 6 and 13years ago were collected, DNA was isolated and the ITS regions were pyrosequenced. Similarly samples were also collected from untreated stumps within the same forest site over the same period of time. A total of 53,117 fungal sequences were generated by 454-pyrosequencing from 18 wood samples. After data cleaning we had 26,127 sequences representing 49% of the original sequences. Possible impact of the treatment on fungal communities in different study sites was analyzed using Principal Component Analysis (PCA). Also diversity indexes and similarity indexes between controls and treated stumps were calculated. Biocontrol P. gigantea represented 0.43% of all fungal sequences and was found only from stumps after one year post-treatment. The pathogen H. annosum s.l. was not observed in this study. Numbers of different OTUs were always higher in the control stumps. However there was no statistical difference noted between treated and non-treated stumps. Based on our results we can conclude that stump treatment should continue as there is no obvious adverse effect on the other stump mycobiota.