Zearalenone, a phytoestrogen produced by various species of Fusarium, regulates perithecial formation in F. roseum ‘Graminearum’. The response is concentration dependent, enhancing at low concentrations (1–10 ng) and inhibiting at high concentrations (10–100 μg). The biological activity can be modified by varying the chemical structure of the parent molecule. Zearalenone binds to mammalian estrogen receptor protein competitively with estradiol. Conversely estradiol binds to specific receptor protein from Fusarium