Trichoderma spp., Bacillus spp. and Pseudomonas spp. isolated from commercial products show biocontrol activity...

This study evaluated the biocontrol potential of ten commercially available microbial soil additives and fungicides against major soil-borne pathogens (Rhizoctonia solani, Fusarium oxysporum, Sclerotinia sclerotiorum and Diaporthe longicolla) to identify immediate, market-ready solutions for farmers, in the case of soil additives without the delay of product registration. In vitro dual cultures demonstrated strain- and pathogen-dependent antagonistic activity, with Pseudomonas and Bacillus being less effective than the tested Trichoderma strains. Regarding bacterial antagonists, the production of volatile organic compounds (VOCs) and lytic enzymes was confirmed in vitro, indicating potential mechanisms of antagonism. Compatibility tests on soybean plants demonstrated no negative effects on germination, overall growth, or nodule abundance in nearly all cases. In greenhouse bioassays, under high R. solani pressure (1.5%) microbial treatments did not significantly restore germination rate and seedling growth. However, T. harzianum T50 (Vitalin Trichoderma) and T. harzianum + P. fluorescens mixture (Trillus), significantly reduced hypocotyl lesion severity and increased the proportion of symptom-free seedlings. Overall, in planta efficacy was highly variable compared to the strong in vitro inhibition. Nevertheless, selected commercial strains show clear potential to mitigate severe disease symptoms under high R. solani pressure.