Be flexible and adapt easily—The great role of plasticity relative to genetic variation for aggressiveness of Fusarium culmorum isolates

The phenotypic variation in an array of pathogen isolates in natural environments can be partitioned into genotypic variation and environmental plasticity. The present study uses a mixed-model approach to partition the relative contribution of both factors among isolates of Fusarium culmorum from natural field populations in various environments. Twenty-eight and 38 isolates from an international collection were phenotyped for aggressiveness and deoxynivalenol (DON) accumulation across two locations during the years 2015 and 2016, respectively, on four winter type cereals as hosts: bread wheat, durum wheat, triticale and rye, thus providing 16 environments. Aggressiveness, measured as Fusarium head blight (FHB) severity, was assessed by visually rating the symptoms of all isolates on infected hosts, and for 10 isolates, additionally the mycotoxin deoxynivalenol (DON) was measured in the grain after harvest. Despite significant genotypic variation among the isolates, the interactions with years and locations explained the largest proportion of variance which disentangled the overwhelming role of plasticity. Host-by-isolate interaction was not significant and no significant (p < .001) change in the ranking of isolates from one host to another was detected. As the main factor of plasticity was isolate-by-year interaction, this implies that seasonal changes might be an important evolutionary driver in F. culmorum populations.