Truffle Production Research Articles

Response of ectomycorrhizal fungus sporocarp production to varying levels and patterns of green-tree retention

Forest management activities can reduce ectomycorrhizal fungus diversity and forest regeneration success. We examine contrasts in structural retention as they affect sporocarp production of ectomycorrhizal fungi (EMF)—a functional guild of organisms well suited as indicators of disturbance effects on below-ground ecosystems. Our results are from an experiment that tests the biodiversity assumptions behind current guidelines for ecosystem management. Ours is the first study complete with pre-treatment data that examines the effects of silvicultural manipulations on both epigeous (mushroom) and hypogeous (truffle) sporocarp production by EMF. We tested the effects of two patterns (aggregated [A], dispersed [D]) and four levels (100, 75, 40, and 15%) of green-tree retention on standing-crop sporocarp biomass for spring and fall fruiting seasons. This study employed a randomized block design that replicated six retention treatments in three locations (blocks). A total of 150 mushroom taxa and 58 truffle taxa were identified from the sample plots. Before treatment, the total number of mushroom taxa for each treatment ranged from 58 to 72 while the total number of truffle taxa ranged from 22 to 29. The pre-treatment condition was characterized by mushroom and truffle total fall biomass exceeding total spring biomass in two of three blocks. Although experimental units within blocks were selected for apparent similarity, our results show that uniformity of EMF populations in forests cannot be inferred from stand structure alone. During the post-treatment sample period, the number of mushroom taxa detected in the 100% retention decreased by 34% while the number of truffle taxa increased by 20%. The number of taxa was reduced most in the 15%D treatment followed by the 15%A treatment. The 75%A retention treatment showed the least reduction in number of fruiting taxa. After treatment, sporocarp production declined in all treatments, but these effects varied by season and treatment. Sporocarp production was nearly eliminated from the 15%A retention treatment. Mushroom and truffle production were significantly reduced in the 15%D treatment, though spring truffle biomass was maintained at 33% of the pre-treatment value. No treatment effect was detected on the fall mushroom or truffle standing crop in the 40%D treatment. Our results lend support to the use of dispersed green-tree retention in combination with aggregated retention when maintaining sporocarp production is a goal. Such a mix would ameliorate the effects of clearcutting as demonstrated in this study and may maintain higher levels of sporocarp production in the aggregates by reducing edge effects.

Tuber aestivum (syn. T. uncinatum) biotopes and their history on Gotland, Sweden

This study aimed at testing the hypothesis that the genetically distinct Tuber aestivum population on the island of Gotland, Sweden, is adapted to habitats different from French T. aestivum populations. The soil structure, soil chemistry, bedrock, climate, vegetation and host tree continuity of 18 T. aestivum sites on Gotland were analysed and compared with data from France. We conclude that T. aestivum can grow in soils with a broad soil structure range and that no striking differences in soil chemistry were found. No T. aestivum indicator plants other than the host trees were found, but the host tree continuity on the T. aestivum sites on Gotland was more than 300 yr. If the T. aestivum population on Gotland constitutes an ecotype it is rather an adaptation to the colder and drier climate on Gotland. Selecting local T. aestivum inoculum for truffle orchards in northern Europe could be important for successful truffle production.

Population genetics and dynamics of the black truffle in a man-made truffle field.

The colonization dynamics of the black truffle in an artificial field were assessed through analyses of microsatellite and RAPD markers. The truffle field was composed of three tree species and mycelial inoculum of three different origins, and was monitored for the first three years of truffle production. We found very low levels of genetic diversity. Isolation by distance was detected only at the between-tree level. This could be interpreted as local colonization around each tree facilitated by the presence of the tree root system. At the larger spatial scale of the European range, the absence of isolation by distance corroborates the hypothesis of an impact of glaciation on genetic variation, followed by rapid postglaciation demographic expansion. In addition, genetic variation of harvested truffles was explained by neither inoculation origin, nor tree species. Our study questions the real impact of man-made inoculation of tree root systems with fungal mycelia.

Improving the production of truffles

Truffles, those delectable fungi used by chefs for flavoring, are hard to find. Truffles (genus Tuber) grow as ectomycorrhizae on roots of trees and shrubs, and are hunted in forest areas using pigs or trained dogs. Demand easily exceeds supply because only ∼20 tons are produced worldwide, and prices can reach US$3000 per kg for white truffles. In recent years, large plantations have been established in southern European countries, New Zealand, Australia and the USA, but close attention is needed to minimize the level of contaminating and competing ectomycorrhizal fungi on the root systems of inoculated plants. However, morphological distinctions are often narrow and rigorous identification impossible. The availability of reliable methodology for identification of contaminants is becoming increasingly important because buyers demand that plantlets from truffle orchards infected with prized species of truffles be certified.Improvements in molecular techniques have now opened up the possibility of using molecular tools to augment or replace traditional morphology. While working to verify the formation of ectomycorrhiza in Tuber-infected seedlings of oak (Quercus pubescens), Antonella Amicucci and colleagues1xMorphological and molecular characterization of Pulvinula constellatio ectomycorrhizae. Amicucci, A et al. FEMS Microbiol. Lett. 2001; 194: 121–125CrossRef | PubMedSee all References1 discovered that the ascomycete, Pulvinula constellatio, formed competing ectomycorrhizal relationships. The authors described the fungus morphologically and adapted a PCR approach for establishing the identity of P. constellatio by developing a restriction-fragment-length polymorphism method, based on the internal transcribed sequence of the ribosomal RNA gene. They showed that the molecular procedure provided a reliable method for showing the presence of P. constellatio.P. constellatio now joins a list of other discomycetes such as Pulvinula globifera and Sphaerosporella brunnea that also compete with Tuber spp. on cultivated seedlings of oak. S. brunnea, in particular, forms mycorrhizae that are morphologically similar to those of the prized white and black species of truffles, Tuber magnatum and Tuber melanosporum, respectively, and thus are difficult to distinguish. The adaptation of molecular probes promises to provide efficient tools that can be used to certify the purity of plants inoculated with edible species of Tuber, thereby helping to increase the availability of uncontaminated truffle-infected plantlets used in artificial truffle cultivation. For those who love good food, this couldn't be better news.

Production, protection et professions truffières

Truffle production, protection and social organisation. This article stresses the analysis of the relationships between domestication truffle process and social organisation evolution. Today, despite low yields and instability, truffle production is always considered more than an agricultural production than an experimental one. All along nineteenth and tiventieth centuries, producers, scientists and traders tried to improve the know-how of this production. The general tendancy of such social oragan- isations is based also on a real ability to maintain and valorize the natural image of the mushroom and to protect the "secret" of its production. Three periods can be distinguished. The first one from 1920 to 1970 testifies the slow dilution of empirical knowledge, induced by the creeping disparition of traditional agriculture. The second period from 1970 to 1990 stresses the importance of new plant variety in a modification of cultivation methods. The third one insists upon the debate between a "statu quo" position and doubt ness induced by the groiving lack of production.

Phosphorus status in some natural desert truffle stands

Little is known about the phosphorus (P) status of non agricultural soils, although some sites in drylands are potentially important for the production of desert truffles, a mycorrhizal association that may overcome the fertility deficiency. In this work we described the fertility characteristics with special emphasis on the P status of some natural desert truffle stands. The soils have poor fertility characteristics and the total P contents range from 32 to 273 mg Kg‐1. The P fractionation shows fairly variable amounts of organic P, while the proportions of the other fractions are related to the soil chemical properties. The available P contents are also variable, but generally high if compared with the critical levels for optimal yields of crops. The water availability of these soils is likely to be an important factor to be kept into account when evaluating the P availability.

Truffle production in old-growth and mature fir stands in northeastern California

Few studies have examined fruiting patterns of hypogeous fungi, and relationships between sporocarp production of hypogeous fungi and forest habitat components such as organic soil depth and amounts of decayed wood are poorly understood. We sampled sporocarps of hypogeous fungi (truffles) in four old-growth (>200 years) and four paired, mature (ca 100 years) fir ( Abies spp.) stands during four sample periods in 1993 and three sample periods in 1994 in the Lassen National Forest in northeastern California. Truffles were collected from 4-m 2 circular plots systematically located at 36 grid points per stand during each sample period. Habitat characteristics were measured in 50.3-m 2 circles centered at each grid point in 1993. We found a total of 46 truffle species in 30.4% of the 2016 total plots, and the total standing dry weight of truffles was equivalent to 2.43 kg ha −1. Total frequency and biomass of truffles and number of truffle species did not differ significantly between stand types in 1993 or 1994, but species composition did. We found no significant associations between measures of total truffle abundance and measures of habitat structure and composition at the 0.25-ha grid scale or at the 50.3-m 2 habitat plot scale. At the scale of the 4-m 2 truffle plot, plots with decayed wood were more likely to have truffles than plots without decayed wood during the final sample period of each year, but the association was significant only in 1993. Mean organic soil depth was greater in plots with truffles than plots without truffles in each sample period in both years, but ranked values were only marginally significant in one sample period. Goodness-of-fit tests to the Poisson distribution indicated that individual truffles had clumped distributions, but we could not reject the null hypothesis of random distribution of truffle collections. Our results indicate that total truffle production had recovered from stand-replacement wildfire in the mature stands, and that total truffle abundance was not strongly associated with habitat characteristics within the range of habitat variation exhibited in these stands. Individual species, however, were associated with old-growth stands and others with mature stands.

Factors affecting yield of Tuber melanosporum in a Quercus ilex plantation in southern France

Yields of Tuber melanosporum fruit bodies from a commercial truffle plantation are examined in relation to time, soil conditions and basal diameter of host tree. Fruiting started 10 yr after planting, and the number of trees producing truffles increased steadily for the following 8 yr. The best predictor of truffle production was tree basal diameter.

Study of important factors affecting the mycorrhizal development of the truffle fungus in the field using plants inoculated in nurseries

In France, plants forming mycorrhizas in nurseries with the truffle fungus ( Tuber melanosporum) have been used for ten years. Much information has been accumulated. To grow plants with mycorrhizas optimally in the field, there are three guidelines: • site selection • choice of tree species best adapted to the selected sites • repeatedly check that conditions remain favourable for truffle production. Site selection is determined by soil texture and fertility both of which can be corrected by applying lime, phosphate and/or potassium, manure. The progress of T. melanosporum is better when inoculated seedlings are planted into land cropped previously by plants that do not form ectomycorrhizas. Soil disinfectants do not reliably eliminate unwanted mycorrhizal fungi. To improve and sustain conditions for good truffle production, soil and tree-maintenance, fertilizer practices and irrigation must be considered. Irrigation is becoming of increasing importance for the consistent production of truffles. In optimal conditions, with Tuber-type mycorrhizas produce truffles within four years of planting.