The suppressiveness is tested for three important mushroom pathogens:

1. Bacterial blotch caused by Pseudomonas gingeri;
2. Two fungal diseases: dry bubble disease caused by Lecanicillium fungicola and wet bubble disease caused by Mycogone perniciosa (Figure 2).

The pathogens are supplemented to the casing soil at the start of the cultivation. During two production cycles (flushes) the disease incidence, the mushroom yield and its quality are measured.

The casing soils are sampled before and during the cultivation to find a relation between the suppressiveness, physico-chemical properties and the microbiome (total of micro-organisms) of the casing soil. Kekkilä-BVB, one of the industrial partners in our project, determines the physico-chemical properties of the casings such as the water holding capacity, the density, the adhesiveness, pH, electrical conductivity, etc.

In later steps, the microbiome analysis will be conducted at CTICH (Project coordinator) in Spain, where the project will also determine if the alternatives are polluted with microplastics, heavy metals or pesticides.

In previous experiments we noticed that the use of some of the alternatives resulted in a lower disease incidence, but never in a full elimination of the disease. To enhance the suppressiveness, bacterial strains of the genera Pseudomonas and Bacillus are selected from casing material that potentially can act as biostimulant. It is important to know how long these biostimulants remain active.

Therefore, specific methods are required to detect the biostimulants in the casing soil. We developed already for 4 out of 5 selected biostimulants TaqMan assays: specific and sensitive detection methods able to quantify the biostimulants in the casing soil (Figure 3). In the next experiments at Inagro (Belgium), the effect of the biostimulants on the diseases will be evaluated.

Figure 3. Left: The TaqMan machine to perform the assay. Right: result of a TaqMan assay to quantify biostimulants in casing soil. The green line is the signal caused by the presence of the biostimulant.