Generally, the commercialized mycorrhizated truffle seedling is associated with the black truffle (Tuber melanosporum), although very recently a small plantation has been realized with summer truffle (Tuber aestivum, Tuber uncinatum), and lately we have also been consulted about Tuber borchii, the whitish or Borch truffle.

In general, what is said about the seedling mycorrhizated with black truffle (T. melanosporum) is applicable to other truffles.

On the one hand, there is the quality of the mycorrhization and on the other, the good quality of the seedling in terms of health, development, type of container, root free of deformations, etc.

In terms of the aspect and development of the seedling, criteria of quality exist that are followed by the technicians of the various local and national governments when it comes time to purchase seedlings for public reforestation. We will describe below the most important points about the holm oak (Quercus ilex), and the Portuguese or gall oak (Quercus faginea), which are the two species most used in truffle plantations.

            – Age: 1,2 years

            – Minimum height: 10 cm for 1 year, 15 cm for 2 years

            – Maximum height: 30 cm for 1 year, 50 cm for 2 years

            – Minimum diameter of the neck of the root: 2 mm for 1 year, 3 mm for 2 years.

            – Minimum volume of the container: 200 cc

            – The consistency of the root ball is a requisite of quality.

Control de calidad de la planta micorrizada con trufa.

Aspect of a well-developed holm oak.

Seedlings with the following defects are not considered to be of top or commercial quality:

            -Absent of buds susceptible to producing apical sprouting.

            – Multiple cuts.

            – Deformed root system.

            – Signs of desiccation, overheating, mold, decay or damage caused by harmful organisms.

            -Imbalance between the aerial part and the root part.

In terms of the quality of the mycorrhization, it should be noted that when talking about a minimum percentage of mycorrhizated apexes, generally a minimum of between 20% and 33% of mycorrhizated apexes is demanded at the ends of the finest roots susceptible to sheltering mycorrhizas. This percentage refers to the fine apexes or finest root ends that can be mycorrhizated. Clearly, a seedling with a poor root development due to inadequate cultivation, poor handling, etc., will have less fine root endings than a seedling with a correct root development. Regarding the first seedling, a low number of mycorrhizas can give us a high percentage of mycorrhization and surpass the minimum requirement, while the second seedling can have a greater total number of mycorrhizated apexes but still not reach the required percentage. With this reflection we want to point out the importance of a good root development. Some control methods for seedlings avoid this problem by speaking of a minimum number of mycorrhizated apexes and not giving all importance to the percentage.

Analizando las raices de una planta trufera.

A well-developed root is necessary for a minimum number of mycorrhizas.

It’s important for a seedling to have an abundant mycorrhization over a well-developed root system, but the real icing on the cake and what makes the seedling of the highest quality is to achieve a mycorrhization exclusively with the target fungus, generally the black truffle (Tuber melanosporum).

Detalle de las micorrizas vistas con una lupa. Cepellón de raices micorrizadas con trufa negra.
Aspect of mycorrhizas viewed throught a steroscopic microscope.   Root ball in wich roots are visible with mycorrhizated ends.

Mycorrhizated seedlings may be rejected for various reasons:

            – For health and/or morphological reasons (insufficient or excessive development, root defects, etc.).

            – Presence of other mycorrhizas belonging to other truffles along with the mycorrhizas of the inoculated truffle.

            -Absence or scarcity of mycorrhizas.

Regarding the presence of fungi in the root other than Tuber melanosporum, various considerations should be kept in mind:

A)    If it is a rival species of the Tuber sp genus, certification methods exist to reject the batch, regardless of the degree of its presence. Generally, various species of Tuber sp can appear (Tuber brumale, Tuber aestivum, Tuber uncinatum, AD type mycorrhizas, etc.), although the most problematic of all these in seedlings mycorrhizated with black truffle is Tuber brumale. With Tuber brumale, the subject is more delicate because the period of its harvest coincides with that of the black truffle, and there are zones where both appear; furthermore, the aspect of their exterior (peridium) and interior (gleba) are similar, above all in some of the various ecotypes of T. brumale, and if, to this, we add that it is common to commercialize “brumale” truffles in percentages of up to 15% mixed with batches of black truffle, we see the danger it represents, and the care and precautions that must be taken when mycorrhizating the black truffle. Contamination with “machenca”, as the brumale truffle is also known, more often affects the hazelnut tree, given that this tree has the natural tendency to more easily enter into mycorrhizal association with Tuber brumale. In recent years, the so-called Chinese truffle has appeared on the European market; it is cheaper and of lower quality and has the serious drawback of being similar in aspect to the black truffle and likewise coinciding in harvest times. Distinguishing the difference between the mycorrhizas of these truffles and those of the black truffle is a matter for specialists. Other fungi that can be competitive with the truffle in plantations are those “basidiomycota” that live in calcareous soils, such as some species of the genus Hebeloma, Cortinarius, etc.

Trufa negra, tuber melanosporum, en el microscopio.

1.-Micorrhizadas of the black truffle.
2.- Surface of the mycorrhiza (mycoclena) with puzzle desing.
3.- Surface of the mycorrhiza with long, non-wavy cystidium.
4.- Aspect of the long, non-wavy cystidium with angles

B)     Other fungi present in the roots of seedlings mycorrhizated with black truffle (or another type of truffle) are the fungi that grow in greenhouse conditions during the seedling’s cultivation. If the interior environment is not correctly managed, the higher temperatures and humidity of the greenhouses favor the rapid development of opportunist fungi that can mycorrhizate the root system of the young seedlings. Mycorrhizations with Sphaerosporella sp, Thelephora sp., etc., can occur. If the truffle is abundantly present in the root of the seedlings, these greenhouse fungi disappear once the seedling is moved to the field because they don’t prosper in outdoor conditions. If their implantation in the root is high, however, it means that the mycorrhiza of the truffle is not abundant and the drawback is then the low mycorrhization of the seedling by the truffle.

Fructifications of Sphaerosporella brunnea, a common contaminant in the greenhouse that can hinder the implantation of the truffle.

C)    Although in Spain it isn’t currently a problem, in Italy seedlings mycorrhizated with Tuber magnatum are commercialized, even though the fungus present in the root belongs totally or partially to other truffles (Tuber borchii, Tuber dryophilum, Tuber maculatum, etc.), given the similarity in aspect of the truffles and of the mycorrhizas of these truffles with the white truffle of Italy.

D)    Although in Spain it isn’t currently a problem, in Italy seedlings mycorrhizated with Tuber magnatum are commercialized, even though the fungus present in the root belongs totally or partially to other truffles (Tuber borchii, Tuber dryophilum, Tuber maculatum, etc.), given the similarity in aspect of the truffles and of the mycorrhizas of these truffles with the white truffle of Italy.

Finally, it should be pointed out that for the best productive results, one must begin with a high-quality seedling. Some aspects of the seedling are clearly visible: we can see if it is well-developed, healthy, has abundant roots, we can see the type of container, if the root ball is compact, etc., but we can’t evaluate its most important aspect: the seedling’s mycorrhization by the truffle. It’s possible that all sellers of seedlings will claim that they sell high-quality seedlings, but even so it’s advisable to verify this at a specialized laboratory. The certification of the seedling by an external body is a good thing, but in the end the seedling delivered to the client is always the responsibility of the supplying company. Currently, the work of the certifying center ends once the results of the control are given to the nursery.

The controls are made on batches and each batch has a specific number of seedlings; each batch of seedlings is generally defined by the same inocula; the inocula consists of truffle spores that come from a specific number of truffles, etc., etc. Sometimes, not all of the controlled batches are suitable for sale, nor are all the batches controlled. Occasionally, it is necessary to make a later control of the same batch or it may simply be invalidated. It is common practice and logical for some truffle growers or associations who are making a combined purchase, to request sample seedlings before planting to examine the batch or batches that they will use to plant. At Cultivos Forestales y Micológicos, we welcome clients and people who wish to see the seedlings at our facilities and we have absolutely no problem if they take or send a seedling to be examined; it’s even recommendable to analyze a seedling upon receiving the order.