A workflow for sourcing and characterizing wheat field microorganisms for the biocontrol of Fusarium head blight

Fusarium head blight (FHB), caused by numerous Fusarium species, is a major fungal disease affecting wheat and other food staples. Biological control agents (BCAs) are promising alternatives to synthetic fungicides for integrated disease management. In the present study, a workflow was developed to isolate and screen wheat field-associated microorganisms for their antagonistic activities against FHB causal agents, by taking into account both intra- and interspecific diversity of pathogen complexes. Non-selective and selective isolation methods were used to collect 1231 bacteria, 365 molds, and 39 yeasts from wheat grains, maize residues, and soil samples. From this collection, microbial antagonistic activities were first determined against a Fusarium graminearum strain, followed by taxonomic identification of positive isolates. Their activity spectrum was also determined against additional Fusarium graminearum strains, as well as Fusarium avenaceum and Fusarium poae. Then, screening of the ten most effective isolates (4 bacteria, 1 yeast-like, and 5 molds: Rahnella aceris, Streptomyces sp., 2 Pantoea agglomerans isolates, Cistella sp., Trichoderma paraviridescens, Trichoderma gamsii, Epicoccum layuense, Podila minutissima, and Penicillium virgatum) on surface-disinfected grains confirmed their ability to control or delay pathogen growth. Significant variations in BCA antagonistic activities were observed among isolates across different Fusarium species and/or strains, which reinforced the importance of including intra- and interspecific pathogen diversity during the screening steps. One T. gamsii isolate emerged as the most promising candidate, achieving complete inhibition of Fusarium growth (100%) and preventing or dramatically reducing mycotoxin production (up to 100% reduction of deoxynivalenol production). This study highlights that wheat fields serve as a valuable reservoir for potential BCAs against FHB control.