Role of enniatins and deoxynivalenol in interspecific growth and competition in vitro among the principal causal agents of Fusarium head blight

Fusarium graminearum and Fusarium avenaceum , causal agents of Fusarium head blight (FHB), are known to produce secondary metabolites such as deoxynivalenol (DON) and enniatins (ENNs), respectively. These species, along with other FHB pathogens, Fusarium culmorum and Fusarium poae , often co-exist in a single host-plant head, potentially resulting in the accumulation of different secondary metabolites. This study aimed to investigate the in vitro role of ENNs and DON in Fusarium development, metabolism and competition. The effects of three concentrations of enniatin B (ENB) and DON, alone or in combination, were assessed on the growth of F. avenaceum , F. graminearum , F. poae , and F. culmorum on potato dextrose agar (PDA). The expression of F. graminearum genes potentially related to stress response, growth and involved in trichothecene biosynthesis, was analyzed to elucidate the secondary metabolite action. The role of ENNs and DON in interspecific competition was explored through dual-culture experiments on PDA and rice flour agar (RFA) using mutant strains of F. avenaceum and F. graminearum . A combination of ENB and DON at the highest concentration (100 mg L⁻¹) had the most significant inhibitory effect on the growth of all tested species. Even at the lowest concentration (10 mg L⁻¹), ENB+DON significantly inhibited the growth of F. graminearum (5%) and F. avenaceum (14%). Gene expression analysis in F. graminearum revealed that exposure to 100 mg L⁻¹ of ENB, DON, or their combination induced a stress response. However, dual-culture experiments demonstrated that ENNs and DON did not play a role in the in vitro interactions between F. graminearum and F. avenaceum . The results obtained may prove useful in shedding light on the competitive dynamics among the various Fusarium species involved in causing FHB, and on how their secondary metabolites may play a role, either alone or in combination, in the development of the disease.