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 Fusarium graminearum, the major cause of Fusarium head blight (FHB) in wheat and deoxynivalenol (DON) accumulation in grains, a workflow consisting of in vitro and in vivo assays was set up. Twenty-one Streptomyces strains, 16 of which were endophytes of different plants, were analyzed. In vitro and in vivo tests characterized their plant growth promoting (PGP) traits. Biocontrol activity against F. graminearum was firstly assessed with a dual culture assay. An in vivo 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 Streptomyces strains. A selected subset of Streptomyces 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 Streptomyces 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.
Highlights
Fusarium graminearum is a major threat to wheat, leading to Fusarium foot rot (FFR) and Fusarium root rot (FRR) (Smiley and Patterson, 1996), as well as Fusarium head blight (FHB), the major cause of wheat losses (Goswami and Kistler, 2004)
Identification of the nine isolates not identified in a previous study (Colombo et al, 2019) by 16S rRNA confirmed that all 21 strains belong to Streptomyces spp. (Table 1)
Streptomyces strains were extensively characterized for their plant growth associated features, together with detailed examination of their activity on germinating wheat and on wheat infected with F. graminearum
Summary
Fusarium graminearum is a major threat to wheat, leading to Fusarium foot rot (FFR) and Fusarium root rot (FRR) (Smiley and Patterson, 1996), as well as Fusarium head blight (FHB), the major cause of wheat losses (Goswami and Kistler, 2004). The pathogen, to other known foot and root rot pathogens of wheat, such as F. culmorum (Scherm et al, 2013) and F. pseudograminearum (Chakraborty et al, 2006), has a specific pathway of infection and spread via roots (Wang Q. et al, 2015). Head blight, root, and foot rot caused by F. graminearum share most of the developmental steps of pathogenicity (Wang et al, 2018), including the DON synthesis (Covarelli et al, 2012)
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