The study “Health-resistant Mushroom Cultivation” is a leading example of cooperation in this sector. In addition to BVB Substrates, the participants are fellow producers CNC, Sterckx and Legro, compost supplier Walkro, spawn producers Amycel and Lambert Spawn and research institute NIOO. In collaboration with the Dutch Ministry of Economic Affairs, they are funding the project through a public-private partnership (PPS). ‘Taking a joint approach to research and innovation will take us forward faster. Broad spectrum knowledge development contributes to greater sustainability in the mushroom chain. This will keep our sector at the forefront internationally’, is how Guido Linders, Director of Business Unit Professional Growing at Kekkilä-BVB, explained the importance at the start of the project in 2016.
Multiple factors affect disease pressure
Now, four years later, new knowledge has certainly been developed, concludes Jan van der Wolf, bacteriologist and project lead at WUR. Together with Jos Amsing of Research & Development at Kekkilä-BVB, he talks about the project at the Wageningen campus. Jos Amsing explains the main research goal first: ‘Mushroom growers want to produce without disease pressure. Ginger blotch, in particular, a bacterial disease of cultivated mushrooms, can cause severe production losses. The bacterium Pseudomonas gingeri causes this disease, which sometimes appears out of nowhere. The reason is unknown. That is what we would like to answer.’
Jos Amsing, Kekkilä-BVB, Researchs BVB Substrates casing soil
However, van der Wolf adds that part of the answer has been identified. ‘We now know that various factors affect the disease pressure. The origin of the peat used in the casing soil appears to have little influence. However, the disease pressure may be lower with certain mushroom varieties or under certain growing conditions. The composition of the casing also plays a role. The fact that there are multiple influential factors means there is not one simple solution to prevent the disease.’
Peat type does not influence mushroom disease pressure
How did the researchers arrive at these results? WUR started the study by testing peat excavated from three locations, both from the airier upper layer and the more compact lower layer. This peat was of course supplied by the casing soil specialists. Researcher Tanvi Taparia, a PhD candidate who hopes to obtain a degree with this study in 2020, performed all experiments together with test farm Unifarm.
Van der Wolf: ‘We examined the samples for microorganisms. In peat of all origins there appears to be a naturally very low density of the pathogenic bacteria. These bacteria do not generally cause any harm. If we artificially add the pathogen, we do not notice any difference in the resistance of peat from different origins. The disease only manifests when the concentration of bacteria exceeds a threshold. For Pseudomonas gingeri this threshold is lower than for Pseudomonas tolasii, which causes “brown blotch”.’
Humidity and varieties have effect
Step two was a test under growing conditions. The beds of mushrooms were contaminated with the pathogen. Some of the beds were sealed with plastic. That had an effect, says van der Wolf: ‘A higher humidity level directly results in a higher incidence of bacterial blotch.’ Jos Amsing adds: ‘That corresponds to what mushroom growers see in practice.’ The researchers also tested four white mushroom varieties and two chestnut mushroom varieties. In one variety, there were higher levels than in others, van der Wolf explains. ‘The difference was more marked between the white mushroom varieties. Growers can base their choice of variety on this information.’
Hunt for beneficial microorganisms
This trial also yielded an unexpected insight. During the first flush (harvest) there was extensive infection by ginger blotch. However, in the second and third flush the researchers saw few affected mushrooms, even though the concentration of the pathogen in the successive flushes increased further. ‘Apparently there are other microorganisms that can counteract the bacteria. Naturally we are very eager to know which these are. Tanvi Taparia is now carrying out a so-called microbiome study. This will identify all the micro-organisms. She will be continuing the data analysis this year’, explains van der Wolf.
Jos Amsing of Kekkilä-BVB adds: ‘That was an interesting outcome for us. Beneficial bacteria can make casing soil more resistant in the future, but further research. Is required’
How productive are sustainable alternatives?
In addition to increasing the resistance of casing, the sector also aims for more sustainable use of raw materials. Black peat extraction is also facing an uncertain future. An alternative is very welcome, preferably one with all the positive properties of peat. Part of the research therefore involved testing three alternatives mixed with black peat: a mixture with BVB Accretio, a mixture with NewFoss-grass substrate and recycled casing soil. These alternatives were either steamed at 70°C or not steamed treated. The researchers compared these alternatives with standard casing soil. Van der Wolf: ‘We tested two aspects: productivity and disease pressure. The experiments were carried out in small trays. We found relatively small differences in productivity between the selected substrates. Steaming did not appear to
have an effect on production.’
Pre-steaming creates resistance
For van der Wolf, the ranking in disease pressure was particularly surprising. ‘When Pseudomonas gingeri was artificially added to the casing, the steamed, recycled casing soil proved to be the most resistant. That was not what I expected. Steaming the casing often appeared to result in higher resistance. There could be certain beneficial, thermophilic micro-organisms that survive steaming. The results of BVB Accretio, the standard casing and the grass substrate did not differ all that much.’
The next question of course is how casing soil suppliers will implement these results in practice. R&D-man Jos Amsing: ‘It is good news for us that the production and resistance of casing soil with BVB Accretio is positive. This can be a step towards a more sustainable mushroom cultivation sector. We are looking for the answers to new questions, such as the beneficial microorganisms and recycled casing. We also hope to perform these follow-ups together with our colleague companies and WUR. Together we can find new puzzle pieces and increase the sustainability of our mushroom chain.’