BLACK TRUFFLE CULTIVATION AND COMPETING FUNGI - Inra

Proceedings of the 7 th International Conference on Mushroom Biology and Mushroom Products (ICMBMP7) 2011
we observe very good results in truffle plantations established in large plains where there are
cereals and vineyards cultivations without any oaks in hedge or woodlands near the plantations.
Chemical fertilizers and soil fertility are not main factors to explain why some plantations cannot
begin to trigger truffle production.
After at least one century of agricultural abandonment, we observe many oak woodland
surrounding truffle plantations. They have grown naturally and progressively. Nowadays, they
are penalizing the truffle production. Their impact depends of the « contaminating reach » of the
oaks (10 meters in average) and of the « power of contamination » of the oaks on the edge. If the
oaks on the edge are grouped in woodlands, their power of contamination is stronger than if they
are in hedge [15]. This situation underlines the necessity to build « truffle bastion » in order to
keep all T. melanosporum strength (power = strength x number of producing truffle trees). In the
heart of big truffle plantations, there is a “truffle bastion” protected against fungi coming from
outside.
The strength of the truffle is stated trough the concepts of « truffle virulence » or « truffle
aggressiveness » which can be observed with “brûlés” spreading or gaining ground in good
truffle plantations. In South-West of France, default of T. melanosporum “virulence” or
“aggressiveness” is generally concomitant of 4 facts: 1) T. brumale is harvested instead of T.
melanosporum, 2) T. melanosporum does not resist well during the drought, 3) truffle production
has not durability in time (tree years in average in wild “truffières”), 4) harvest starts later in
plantation after many years (as if there was an inertia to fruiting).
After the characterization of the lack of the truffle virulence, we can propose the opposite
arguments to define positive truffle virulence. Many experiences or trials are done at the Station
of experimentation on the truffle at Cahors-Le Montat and in some truffle areas in France and
abroad. For these trials, we study another factor which could be the impact of the domestic
animals like sheep and horses. We had observations which involve these animals in exceptional
truffle production fields. We can suggest an analogy with other mushrooms production: Agaricus
campestris L. and Pleurotus eryngii (De Cand.:Fr.) Quélet need respectively in their grassland
habitat cows and sheeps.
We humbly recognize some explanations are still lacking. Why in 2006 (a good climatic
year), the Lot district did produce 3 tons of truffles whereas its production was more that 300
tons in 1906? This 100 factor seems to summarize this lost of “virulence” or “strength” of the
black truffle. This decline is usually explained by the deterioration of the T. melanosporum
ecosystem, consequences of changes in human activities, mainly agriculture, animal farming and
forestry. With less traditional activity, oaks woodlands are more and more present with their
fungi of forest ecology.
Why is the black truffle less dominant than in the past, why does it defend less against its
potential aggressors? This is the double question asked in the introduction. Does sick black
truffle like other mushrooms suffer pathogen attacks like virus? This hypothesis is supported by
some scientists [16] to explain the difficulty of truffle production. In this article, we favour that,
during the abundance period, there were practices of mixed farming with organic matter
restitution, biodiversity management. The rural world was entirely exploited and cultivated.
Population density in the country was higher than today. Woodlands were rare and firewood was
precious and collected. In limestone areas, landscapes were very open for the pioneer fungi like
T. melanosporum: its “strength” or “virulence” was at the optimum. Furthermore, the harvesting
pressure was lesser than nowadays, leaving in the soil a lot of truffle spores useful as natural
inoculum. There were no inoculated controlled mycorrhized plants to sell and buy; nevertheless,
there was an abundance of truffles.
Section:
Mycorrhizal mushrooms
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