Mushroom cultivation is a growing field both in Estonia and worldwide, covering not only edible and medicinal mushrooms but also yeasts and biocontrol antagonists. According to Kalev Adamson, associate professor at the Estonian University of Life Sciences, broader use of fungi could help add more value to local forestry and agricultural waste.

Mushrooms have been cultivated industrially in Estonia to some extent since the 1970s. Companies have come and gone, but Adamson believes there is still room for growth in the local sector. "If you pick up a box of mushrooms in a store and look at the country of origin, it often says Poland. There isn't a huge amount of local produce," he notes.

Since mushroom cultivation is developing globally, including in Estonia, Adamson is now contributing to its advancement as an associate professor at the university. In his venia legendi lecture on June 12, he discussed recent trends in the field, including growing edible mushrooms on clear-cut areas, cultivating chaga (Inonotus obliquus), and fungal viruses that alter mushroom properties.

In Estonia, oyster mushrooms, shiitake, and lion's mane (often marketed as a health product) are already cultivated. Yeasts are also produced, and mushroom-based biofungicides are developed. "Quite a few companies are already growing mushrooms in Estonia, both for food and other purposes. So it's certainly worth pursuing these topics," the associate professor says.

Stumps and dowels

One line of research by Kalev Adamson and researcher Marili Vester has examined mushroom cultivation in the Järvselja training and experimental forest. Specifically, they used stumps left behind after thinning operations in mixed forests.

"We have grown various edible mushrooms there over several years—around four to five species: oyster mushroom, phoenix oyster, and velvet shank," Adamson explains.

The research group inoculated the stumps with selected species in spring 2024 using mushroom dowels. Since some species take longer to fruit, final conclusions cannot yet be drawn. "Some mushrooms require the substrate to be fairly decomposed — the stump needs to be quite decayed before fruiting begins. For those, we're only expecting the first harvest this year," he says.

However, it is already clear that not every strain works on every type of stump. The experiment used stumps of birch, black alder, and aspen. "Aspen gave the poorest results. Broadly speaking, black alder performed best," he notes. At the same time, a strain that thrives on alder may not grow as well on birch.

The experiment also showed that outdoor mushroom cultivation in summer comes with the challenge of slugs. "In areas with a lot of slugs, they tend to eat most of the crop," Adamson points out. However, species like velvet shank can be grown in winter temperatures below freezing, when slugs are no longer a threat.

Another challenge is competition from naturally occurring fungi. Due to this competition, growers should not expect 100% success, especially at the beginning.

For comparison, the team also inoculated stumps in a clear-cut area. Results were poor because open areas become hot and dry in the sun. In contrast, thinned forest provided just the right level of shade and moisture. According to Adamson, forestry and mushroom cultivation can go hand in hand: "While managing a forest, you can simultaneously try growing mushrooms and hope to harvest a yield."

He warns, however, that installing the dowels is labor-intensive, and the stumps must be monitored weekly. "It's also very time-consuming: you have to walk through all the stumps, count how many fruiting bodies have appeared, note the dates, and so on," he explains.

It is still too early to give firm recommendations to growers, as stump decomposition takes years. The rate depends on size, diameter, height, and tree species. "At least three to five years, depending on the species, is the time it takes for the fungus to fully colonize the stump and start producing its most vigorous yields," Adamson explains.

In other words, some harvest can be expected in the first year, but not a dramatic result. Still, Adamson believes that refining the method could improve success rates. "Once the best fungal strain is selected for each tree species, the next step is to experiment with different inoculation methods to further improve outcomes," he says.

Exploring fungal viruses

According to Adamson, the focus of the professorship is not only on edible mushrooms but also on medicinal fungi and fungal viruses. Among medicinal fungi, he is particularly interested in chaga, which has received much media attention in recent years. "Its inoculation success rate has been modest — one goal is to improve that," he notes.

The first fungal viruses were discovered in 1960, and since then they have been used to alter fungal traits. For example, viruses can inhibit growth, kill the fungus, slow its development, or change its appearance.

"In species like oyster mushrooms and velvet shank, fungal viruses have been extensively studied, and managing them has become a specialized field," Adamson explains. Until now, no fungal viruses had been identified in chaga. "Now we've successfully isolated the first ones in the lab, and publication is coming soon," he reveals.

During the professorship, Adamson aims to explore the potential of fungal viruses: whether they can suppress harmful fungi or, conversely, make certain species more beneficial for humans. At the same time, he is interested in edible mushrooms: "I'm studying how their cultivation could be improved and how forestry residues could be used more effectively, helping to achieve circular economy goals."

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