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Digital Object Identifier (DOI): 10.6092/issn.2531-7342/6346
The history of truffle cultivation, especially the harvesting of truffles in natural forests with varying degrees of maintenance, dates back centuries. Over time, truffle growers have developed numerous empirical techniques to enhance and sustain truffle production.
Among these, the application of truffle spores is a common practice and can take several forms. For instance, a mixture of water and spores can be dispersed around the trees or applied to specific parts of the brûlé (the bare soil area around host trees). Solid mixtures are also used, prepared by crushing truffle fruiting bodies and blending them with a substrate such as vermiculite. These mixtures are then placed into “traps” — holes of varying sizes dug into the brûlé.
These spores are believed to promote the initiation of truffle sexual reproduction, ultimately leading to the formation of ascocarps (fruiting bodies) — a topic that will be further discussed in subsequent articles. Although time-consuming and potentially costly (due to the price of ascocarps), this practice is widespread among truffle growers, even though its scientific evaluation has been relatively limited.
To rigorously assess the technique’s effectiveness, researchers must partner with truffle growers capable of implementing long-term experiments with consistent and reliable data collection.
It is thanks to such a collaboration that Claude Murat and colleagues were able to evaluate the “Bonneau” inoculation method, developed by Lucien Bonneau.
In this study, published in 2016 in the Italian Journal of Mycology, the authors analyzed the results of a field trial conducted in a 3.5-hectare truffle orchard in southwest France. The orchard was planted in 2007 with 954 downy oaks (Quercus pubescens) inoculated with Tuber melanosporum when they were one to two years old.
Out of the entire orchard, 196 trees were selected in March 2013 for the installation of truffle traps using the Bonneau method. Four pits, each 20 cm wide and 5 to 8 cm deep, were dug at a distance of 50 cm from the trees, in the four cardinal directions. Each pit received 250 mL of a substrate composed of 250 g of frozen T. melanosporum ascocarps, 350 g of honey, 50 L of horticultural vermiculite, and 50 L of compost.
Once the mixture was placed at the bottom of each pit, the original soil was carefully replaced to complete the inoculation process. Harvest data from the 2012/2013, 2013/2014, 2014/2015, and 2015/2016 seasons were meticulously recorded and analyzed. These data allowed for a comparison between:
1 – Trees with and without traps
2 – The inoculated surface (area of the four traps) and the non-inoculated brûlé surface.
Although the first truffles were harvested during the 2012/2013 season (five years post-planting), yields remained very low during the first two years (30 g in 2012/2013 and 2 kg in 2013/2014). As a result, the authors focused their analysis on the 2014/2015 and 2015/2016 seasons.
In 2014/2015, production significantly increased, reaching around 27 kg of truffles in the entire orchard. Of this total, trees equipped with traps yielded 11.8 kg — an average of 61 g per tree. This was three times higher than trees without traps, which averaged 20 g per tree.
However, when considering only the productive trees, there was no significant difference between the two groups: inoculated trees produced an average of 208 g of truffles, while non-inoculated trees produced 200 g on average. In other words, once a tree began producing, it yielded roughly the same amount whether or not it had traps.
Interestingly, the location of the truffles varied significantly. Around inoculated trees, truffles were overwhelmingly harvested from the traps themselves — 96% of them in the 2014/2015 season. Some traps yielded more than ten truffles, and harvesting four truffles per trap was common. Notably, these traps occupied only about 5% of the total brûlé surface. When normalized by area, the yield of inoculated zones was far higher: 362 g/m² versus only 0.9 g/m² in non-inoculated areas.
In addition, the proportion of productive trees was significantly higher among those with traps (approx. 30%) compared to those without (approx. 10%). Although production dropped during the 2015/2016 season, likely due to unfavorable weather, similar trends were observed:
8% of inoculated trees produced truffles, compared to only 3% of non-inoculated ones
The average yield per tree was higher with traps (19 g/tree vs. 7.4 g/tree)
Among productive trees only, average yield was lower with traps (125 g/tree) than without (267 g/tree)
However, area-based yield was still significantly higher with traps (35 g/m² vs. 4 g/m²)
In this Tuber melanosporum orchard in southwest France, the authors observed that adding a substrate mixed with spores into pits had a clear impact on truffle production. Specifically, this method increased the number of productive trees among those with traps, which can contribute to overall higher yields.
Furthermore, the vast majority of truffles around inoculated trees were found inside the traps, with yields sometimes exceeding ten truffles per trap. This suggests that the substrate, composed of ground truffles, compost, vermiculite, and honey, may indeed promote truffle formation. That said, several methodological points, while not undermining the study’s quality, should be considered when interpreting the results:
The experiment was conducted in a single orchard, and the effects of traps may vary depending on soil and climate conditions or management practices. In this trial, all trees with traps were located in the first 2.5 rows of a 12-row parcel (each with 78–81 trees). The design does not follow a randomized block protocol, which would better account for within-field variability.
This setup does not allow for isolating the specific contributions of each substrate component to the observed effects. Vermiculite, compost, honey, ground truffles, and even the soil disturbance caused by digging could all have influenced local conditions and promoted fruiting.
The authors favor the hypothesis that spores from the crushed truffles stimulated sexual reproduction and increased truffle formation. To confirm this, future experiments should include control traps without spores (to be discussed in (see article 01-03).
Truffle traps could help improve Tuber melanosporum production, which likely explains their widespread use among truffle growers. However, the trap setup — including pit size, substrate components, and spore concentration — can affect their effectiveness and deserves more in-depth investigation.
Since traps tend to concentrate the bulk of truffle production in the brûlé, they also offer valuable opportunities for in-field research into truffle biology — particularly the potential role of spores in sexual reproduction (see article 01-03).
Finally, this study highlights the critical importance of collaboration between scientists and truffle growers. Although many of these practices are rooted in tradition, their precise effects are not always well understood. Researchers rely on truffle growers, who are the true field experimenters — but to address practical questions, they also need scientifically robust data.
WETRUF has a team of scientists with extensive experience in field trials. Don’t hesitate to contact us before setting up your own experimental plots!
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