Influence of elevated CO2 concentrations on the growth of Armillaria ostoyae (Romagn.) Herink rhizomorphs in vitro

A comparative experiment was carried out in growth chambers to determine the effects of elevated CO2 concentrations (either 760 ppm or 1,140 ppm) versus ambient CO2 conditions on the growth of Armillaria ostoyae (Romagn.) Herink rhizomorphs, which is the infectious organ of a fungal pathogen affecting many forest trees. We found that one out of three isolates in the experiment differed significantly in rhizomorph production, which was measured as rhizomorph dry mass/100 days of growth. Rhizomorph production was also affected by the tree species used as a food source in the inoculum preparation, with beech wood being significantly different from oak and hazel. Under higher CO2 regimes the production of rhizomorphs was consistently lower for all three isolates compared to ambient CO2 concentrations. For one isolate (no. 11) the growth differences were significant between 380 ppm and both elevated CO2 concentrations (760 ppm and 1,140 ppm), while for the other two (no. 30 and 32) significance was observed only between 380 ppm and 760 ppm. No statistically significant differences have been noted between 760 ppm and 1,140 ppm CO2 for these two isolates. it was concluded that elevated concentrations of CO2 inhibited A. ostoyae rhizomorph growth and therefore have the potential to lessen the pathogenicity of the fungus