Selection of an Endophytic Streptomyces sp. Strain DEF09 From Wheat Roots as a Biocontrol Agent Against Fusarium graminearum

Abstract

Selection of biological control agents (BCA) profits from an integrated study of the tripartite interactions occurring among the BCA, the plant and the pathogen. The environment plays a crucial role in the efficacy of BCA, therefore, the selection process shall utmost mimic naturally occurring conditions. To identify effective biocontrol strains against <i>Fusarium graminearum</i>, the major cause of Fusarium head blight (FHB) in wheat and deoxynivalenol (DON) accumulation in grains, a workflow consisting of <i>in vitro</i> and <i>in vivo</i> assays was set up. Twenty-one <i>Streptomyces</i> strains, 16 of which were endophytes of different plants, were analyzed. <i>In vitro</i> and <i>in vivo</i> tests characterized their plant growth promoting (PGP) traits. Biocontrol activity against <i>F. graminearum</i> was firstly assessed with a dual culture assay. An <i>in vivo</i> germination blotter assay measured Fusarium foot rot and root rot symptoms (FFR-FRR) reduction as well as growth parameters of the plant treated with the <i>Streptomyces</i> strains. A selected subset of <i>Streptomyces</i> spp. strains was then assessed in a growth chamber measuring FFR symptoms and growth parameters of the wheat plant. The approach led to the identification of an effective <i>Streptomyces</i> sp. strain, DEF09, able to inhibit FHB on wheat in controlled conditions by blocking the spread of the pathogen at the infection site. The results were further confirmed in field conditions on both bread and durum wheat, where DEF09 decreased disease severity up to 60%. This work confirms that FRR and FFR pathosystems can be used to identify BCA effective against FHB.