Influence of O2 and CO2on fungal development and hydrophobin expression during the interaction between Heterobasidion parviporum and Phlebiopsis gigantea

Abstract

AbstractHeterobasidion annosum is a very destructive fungal pathogen causing massive losses on forest trees in the northern hemisphere. Tree infection usually takes place through the cut surface after felling. Phlebiopsis gigantea is commonly used as a biological control agent, applied directly after cutting on the stump surface. We investigated the interaction between both fungi in different gas compositions with lowered O2 (0.1% and 0.4%) and enhanced CO2 (15%) concentrations, imitating conditions as present on the wood surface and inside living wood tissue. When grown under 0.1% O2 and 15% CO2, fungal development of both species was altered, growth rate of P. giganteawas decreased and of H. parviporum slightly increased. Low O2 and high CO2 induced the formation of highly hydrophilic tissue with impaired conidia formation and germination capacity. In H. parviporum,this effect was more striking after 7 dpi with 45% reduced vitality, in P. gigantea after 14 dpi with 89% vitality reduction. These observations suggest that entering the tree through the cut surface is accompanied by altering fungal tissue to be more hydrophilic with a concurrent reduction of conidia formation and germination. Expression of the hydrophobin genes HAH1 and HAH2 of H. parviporum at ambient air decreased significantly in response to fungal interaction with P. gigantea. Gene expression was also influenced by O2 and CO2 content. Reduction of O2to 0.4% led to significantly decreased transcription rate of both HAH1 and HAH2 in single and dual cultures.