Efficacy of the Complex Bioproduct Sclerocid® and its Microbial Constituents against White Rot and Associated Soil-Borne Pathogens

Climate change represents a major challenge for agricultural production today. Sclerotinia sclerotiorum (Lib.) de Bary is a necrotrophic pathogen capable of affecting over 500 species of dicotyledonous plants, leading to severe global economic losses. S. sclerotiorum also has developed highly resilient structures—sclerotia—that make this pathogen extremely difficult to control, as they can remain viable in the soil for 4-10 years. This study investigated the efficacy of the multicomponent bioproduct Sclerocid® as a science-based strategy for improving agroecosystem resilience.

Research on the reproductive potential of S. sclerotiorum revealed that under favorable conditions, it can form up to 6 generations of sclerotia, with each mother structure capable of producing approximately 20 daughter sclerotia. Experiments using successive transfers on potato dextrose agar medium recorded specific counts of 31, 30, 18, 19, 20, and 18 new sclerotia per generation, respectively. New sclerotia appear on days 3–4 and reach full maturity by day 7. Furthermore, sclerotia in the soil act as ecological reservoirs for other pathogens, including the genera Aspergillus, Fusarium, and Penicillium, which increases the overall disease pressure on host plants.

Since the superior ability of S. sclerotiorum to persist in the soil makes it difficult to control with conventional pesticides, biocontrol agents represent a promising strategy. Consequently, the biofungicide Sclerocid®, based on a microbial consortium with antagonistic properties, was developed by the BTU Biotech company. The decision to test a microbial consortium was made due to the robustness and synergistic interactions of multi-strain communities. While highly specialized mycoparasites like Paraphaeosphaeria minitans effectively destroy sclerotia, they have a narrow host range and do not control the associated soil-borne pathogens. By combining compatible strains of Trichoderma and Bacillus species, the inhibitory action of the consortium significantly exceeds that of individual monocultures.

The efficacy of Sclerocid® is based on the activities of its specific microbial constituents. Paraphaeosphaeria minitans IMV F-100120 acts as a specialized hyperparasite, colonizing sclerotia and forming pycnospores that lead to their degradation. Trichoderma harzianum IMV F-100097 is a broad-spectrum hyphal mycoparasite that effectively inhibits the growth of associated pathogens, including Alternaria alternata, Verticillium lateritium, Drechslera sorokiniana, and Cladosporium herbarum. Additionally, Bacillus subtilis IMV B-7678 and B. licheniformis IMV B-7778 produce a range of antifungal metabolites, with B. subtilis demonstrating 100% inhibition of S. sclerotiorum. The Sclerocid® consortium demonstrated high biocontrol efficacy, showing inhibition rates of 91.2–100% against S. sclerotiorum and effectively suppressing other pathogens such as Botrytis cinerea (80.4–100%) and Fusarium solani (74.2–100%). Furthermore, joint cultivation trials showed that the microbial component P. minitans could suppress the development of white rot mycelium for up to 35 days.

The synergistic action of the consortium—combining sclerotia hyperparasitism, hyphal degradation, and induction of systemic plant resistance—provides a sustainable and efficient biological solution to control phytopathogens and reduce pesticide load.