Junker, C., de Vries, J., Eickhorst, C. and Schulz, B. 2017. Each Isolate of Hymenoscyphus fraxineus is an Individualist as Shown by Exoenzyme and Growth Rate Profiles. Baltic Forestry 23(1): 25-40.

   Isolates of Hymenoscyphus fraxineus, the causal agent of ash dieback, were analyzed for growth rates and production of the exoenzymes β-glucosidases, amylases, cellulases, lipases, laccases, phenoloxidases, peroxidases and tyrosinases. None of the 176 isolates from diverse locations in Germany, Poland and Sweden secreted all of these enzymes. Growth rates also varied considerably, under the conditions studied between 0.03 and 0.28 cm / day. Additionally, we found inter- and intrapopulation diversity regarding exoenzyme profiles and growth rates among and between the isolates from the Elm forest and a tree nursery in Ellerhoop, both locations in northern Germany. There were no correlations between number of enzymes an isolate produces and growth rate, nor between either growth rate or number of enzymes and virulence, virulence having been determined in a previous study. These phenotypic results concur with previous genetic analyses that have found significant inter- and intrapopulation variability at the molecular level. Only considerable sexual reproduction can explain these results. We conclude that each isolate of H. fraxineus is an individualist.

Keywords: Exoenzymes, growth rate, ash dieback, Hymenoscyphus fraxineus, inter- and intrapopulation variation