Adaptation and response to mycotoxin presence in pathogen-pathogen interactions within the Fusarium genus

The ability of fungal plant pathogens to exude bioactive compounds is an important element of competition in a changing environment. The filamentous fungi usually retain a number of adaptations related not only to the production of toxic compounds by themselves but also to the mitigation of exogenous influences by toxins present in the environment. We examined a distinct effect of toxins on morphology, growth patterns and gene expression after stimulation in mycotoxin-producing and nonproducing isolates representing four evolutionarily divergent species (and chemotypes) within the Fusarium genus (Fusarium graminearum, Fusarium oxysporum, Fusarium proliferatum and Fusarium verticillioides). The aim of our work was to investigate the influence of mycotoxins present in the environment on fungal isolates belonging to evolutionarily divergent complexes within Fusarium genus. The results point to retention of resistance mechanisms in non-producer isolates (F. oxysporum) and specific dose-dependent differences in response to other mycotoxins. In particular, the growth of Fusarium graminearum (confirmed zearalenone and trichothecene producer) was shown to be significantly inhibited by fumonisin B-1 and deoxynivalenol. Conversely, spread of Fusarium verticillioides was accelerated by low concentrations (0.5 mg/l) of nivalenol and zearalenone and deoxynivalenol addition resulted in upregulation of the fumonisin poliketyde synthase (FUM1). The basics of competition between divergent fusaria can be described by 'rock-paper-scissors' theory, but some of the effects can be explained by other interactions, e.g. autotoxicity of deoxynivalenol and the potential role of low doses of trichothecenes and zearalenone acting as a 'warning signal' for competing species.