In vitro optimization of Swedish chaga (Inonotus obliquus) : the path to chaga cultivation in Sweden

Abstract: Chaga has become more popular in recent years as a beneficial natural supplement and wellness tea. Understanding chaga source limitations and its harvest dynamics as well as it’s potential revenue streams would be important for future chaga growers in Sweden. Under natural conditions, the fungus Inonotus obliquus takes many years to establish and develop sterile conks that are then able to be harvested. Cultivating the fungus in forests for profitability therefore would be best optimized by choosing isolates that can establish more quickly. In this study, the growth of I. obliquus was analysed from 10 samples collected across a climatic gradient in Sweden, on three different nutrient media and at three different temperatures, in order to select superior isolates that can be used for cultivation and under optimal conditions for mass inoculum production. The results showed significantly higher mycelium growth on yeast agar (YA) and potato dextrose agar (PDA), compared to birch agar (BA). No significant difference was found in growth rates between samples originating from the North (64° North) and the South (56° North) of Sweden. Highest growth rate occurred at 16°C, followed by 20°C and finally 26°C and this was consistent across all three media tested. In addition to the in vitro growth trials, the degree of pigmentation was assessed in each culture, as pigmentation is commonly an indicator of the presence of melanins which are known bioactive secondary metabolites. Results showed that the fungus growth on PDA and YA exhibited more pigmentation than BA. Interestingly the isolate showing highest growth (S4) showed least pigmentation, and conversely the isolate showing least growth (S3) produced the highest number of highly pigmented petri plates. This may indicate a potential trade-off between primary and secondary metabolite production and ought to be investigated in more detail in future growth optimisation experiments. From the results we recommend future in vitro cultivation of chaga Inonotus obliquus in YA at least as low as 16°C. Further in vitro optimisation experiments could investigate lower temperatures to find the optimal growing temperature.