Killing or modulating : selection strategies of Streptomycetes limiting trichothecene type B production in cereals affected by Fusarium

Streptomycetes are an important group of soil inhabiting bacteria, major producers of secondary metabolites that find application in medicine and agriculture. Streptomycetes can also interact with plants behaving as endophytes. Their diversity represents an interesting source for developing new biological control agents. Selection of antagonists able to limit toxin production can focus on the ability to modulate the toxin pathway or on the ability to limit fungal growth by impairing fungal development and consequently toxin production. Two phenotyping methods for selection based on fungal growth and trichothecene type B inhibition in the wheat-fusarium pathosystem have been employed in order to identify effective antagonistic strains within a 1500 streptomycetes historical collection obtained from plants and soil worldwide. From our preliminary screening it is evident that control of toxins production can be achieved more effectively and consistently by direct inhibition of fungal growth. Strains employed as potential modulators of toxin production when fungal growth is already established were not able to provide consistent and significant protection against toxin accumulation. By integrating the data from the two previously mentioned screening methods, strains of Streptomyces which showed promising results both in vitro and in vivo (grain storage simulation) were selected for deciphering their mode of action against fusaria.