Interactions among Fusarium, streptomycetes and wheat grains: effects on deoxynivalenol accumulation and fungal growth

Streptomycetes have been exploited as biocontrol agents (BCAs) against plant pathogens for their ability to produce different bioactive compounds. They can be used against Fusarium graminearum, the main causal agent of Fusarium head blight (FHB) as well as against contamination of grains with deoxynivalenol (DON). In the present research, the effect of four promising Streptomyces strains on fungal growth and mycotoxin production on sterilised seeds was assessed. The reciprocal interactions between the pathogen and the four BCAs were assessed directly on sterilized grains using quantitative real-time PCR detection of the two targets (Fusarium and Streptomyces spp.) and chemical extraction and quantification of ergosterol and DON. The results indicate that the highest level of DON inhibition (99%) as well as a strong reduction of fungal biomass can be achieved following a simultaneous inoculation of each BCA with the pathogen while late BCA inoculation (3 days post fungal inoculation) did not significantly reduce fungal growth and mycotoxin production. This research contributes also to the understanding of the mechanisms of action of the four Streptomyces strains that act mainly as fungal growth inhibitors. The presence of the fungus influenced differentially the growth of the four strains. This information is important for understanding the fitness of each BCA strain. Our study confirms the importance of studying the interactions among the grains, the pathogen and the BCA, in order to identify mechanisms of activity of the strains, moving towards their application in real conditions.