Streptomyces spp. as biocontrol agents against Fusarium species

"Streptomycetes are the largest taxon of antibiotic producers in the microbial world. Nevertheless, they are less studied than other biocontrol agents against Fusarium diseases and, perhaps, plant diseases in general. Plant diseases incited by Fusarium species are notably challenging. Four species complexes in the genus are pathogenic: Fusarium fujikuroi, F. graminearum, F. solani and F. oxysporum. Being a vascular pathogen, F. oxysporum is particularly difficult to control by using microbial antagonists. Most research has remained at early experimental stages, and only few Streptomyces spp. strains have been assayed under diverse conditions. Few commercial products consisting of Streptomyces spp. have often provided fluctuating results across trials. Five biocontrol trials conducted in the field using streptomycetes report reductions of diverse Fusarium wilts by 0-55%, with one case (cucumber) of yield increase by 1.3-fold. Among 38 articles dealing with potexperiments, 16 report a disease control level above 50%, seven of which with a level above 70%. The chitinolytic activity of Streptomyces spp. strains plays an important role in the biocontrol of Fusarium diseases, and the plant growth promotion trait is a cherished outcome. More attention is being paid to strains endophytic, producing volatile organic compounds, or to the identification of antibiotics and metabolites responsible for the biocontrol. Bioformulation is a critical point in the use of biocontrol agents, but it has been still poorly considered in the experiments. The biocontrol efficacy of well-designed streptomycete consortia or the so-called microbial synthetic communities, possibly in proper bioformulations, and the role of streptomycetes in the reduction of mycotoxins in the grains are aspects that would merit further investigation in the future."