Scandinavian Journal of Forest Research, 2009; 24: 38Á54 ORIGINAL ARTICLE Truffle cultivation in Sweden: Results from Quercus robur and Corylus avellana field trials on the island of Gotland CHRISTINA WEDE´ N1, LINA PETTERSSON2 & ERIC DANELL3 1Division of Pharmacognosy, Department of Medicinal Chemistry, Uppsala University, Uppsala, Sweden, 2Kalmar- Kronoberg County Agricultural Society, Va¨xjo¨, Sweden, 3Museum of Evolution, Botany Section, Uppsala University, Uppsala, Sweden Abstract The edible, ectomycorrhizal Burgundy truffle, Tuber aestivum Vitt., grows naturally on the islands of Gotland and O¨ land, Sweden. In 1999, 240 inoculated Quercus robur and Corylus avellana seedlings inoculated with French T. aestivum were planted in 10 experimental truffle orchards (truffie`res) on Gotland to investigate the possibility of truffle cultivation in Sweden. Truffle orchard management, mycorrhizal development and seedling growth were studied. Fourteen additional truffle orchards containing more than 2000 Q. robur were established during 2000 and 2001. In 2004, T. aestivum mycorrhizae were detected in all truffle orchards. In 2005, the first T. aestivum truffle was found, 6 years after planting. This is the first cultivated truffle in Scandinavia and despite the northerly location they were produced within a timescale comparable with France. Tuber aestivum mycorrhizae survived in soils which differed from naturally producing locations by having a sand content 95%, pH 56.4 and calcium content 50.1%. In a second series of experiments Swedish Q. robur, C. avellana and Carpinus betulus seedlings were inoculated with Swedish T. aestivum. Eleven months after inoculation T. aestivum mycorrhizae were found in 0Á78% of the seedlings, depending on species, inoculation treatment and substrate. Because of the continuing decline of oaks in Sweden and associated fauna and flora, truffle cultivation may favour oak forest restoration programmes as well as making a direct contribution to rural economies. Keywords: Carpinus betulus, Corylus avellana, mycorrhiza, Quercus robur, truffle cultivation, Tuber aestivum, Tuber uncinatum. Introduction T. aestivum is used throughout this article. Owing to its hypogeous nature, truffle spores are not spread by Truffles, the macrofungi forming underground (hy- wind or water, but instead at spore maturity the pogeous) fruit bodies, belong to diverse groups of truffle fruit body emits volatile sulphurous hydro- both ascomycetes (spore sac fungi) and basidiomy- carbons that attract potential spore vectors such as cetes. Most truffle species live in ectomycorrhizal rodents or deer (Bellina-Agostinone et al., 1987; association with various trees and shrubs. Ascomy- Trappe, 1988; Trappe & Castellano, 1991). These cete truffle species are commonly referred to as ‘‘true eat the truffle and spread concentrated packets of truffles’’ and basidiomycete truffles as ‘‘false truf- spores in the faeces. The volatile substances are also fles’’. Several members of the true truffle genus Tuber the reason why some truffle species are highly are highly appreciated as delicacies. One of these appreciated as delicacies that command high prices species is the black Burgundy truffle (Tuber aestivum on the world market (Olivier et al., 1996). The Vitt. syn. T. uncinatum Chat.), which in Scandinavia market demand has also led to the development of is known from the islands of Gotland and O¨ land commercial truffle cultivation on inoculated tree (Sweden) and from Denmark. Since T. uncinatum is seedlings over the past two centuries (Chevalier & a synonym for T. aestivum (Paolocci et al., 2004; Frochot, 1997a). The Burgundy truffle forms ecto- Wede´n, 2004; Wede´n et al., 2005), the older name mycorrhizae with, for example, oak (Quercus spp.), Correspondence: C. Wede´n, Division of Pharmacognosy, Department of Medicinal Chemistry, BMC, Box 574, Uppsala University, SE-751 23 Uppsala, Sweden. E-mail: [email protected] (Received 27 May 2008; accepted 17 October 2008) ISSN 0282-7581 print/ISSN 1651-1891 online # 2009 Taylor & Francis DOI: 10.1080/02827580802562056 Truffle cultivation in Sweden 39 beech (Fagus sylvatica), hornbeam (Carpinus betulus), augment truffle production over time (Chevalier & linden (Tilia spp.) and hazel (Corylus spp.) (Cheva- Grente, 1979). This form of truffle cultivation is still lier & Frochot, 1997a). The natural geographical practised today, and is referred to as the Talon distribution of T. aestivum ranges from North Africa method. The mutualistic relationship between fun- to Sweden and from Ireland to Russia (Chevalier & gus and tree was postulated by Frank (1885), who Frochot, 1997a; Wede´n & Danell, 1998). Tub er discovered the association between T. aestivum aestivum, found in 1997 at a new site on the island mycelia and fine roots, naming it mycorrhiza (Gr. of Gotland, had large fruit bodies with mature spores mykosfungus and rhizaroot). With this new suggesting good adaptation to soil and climatic understanding of the T. aestivum life cycle, and that conditions (Wede´n & Danell, 1998). Before this, of many other fungi, Malenc¸on (1938) introduced T. aestivum had been reported only three times from the idea of planting seedlings already harbouring Sweden (Gotland) and was considered endangered truffle mycorrhizae. When wild truffle harvests in and extremely rare (Larsson, 1997). In 1998, the France, Italy and Spain progressively decreased landowner of the newly discovered site found 5 kg of during the first part of the twentieth century, the T. aestivum within an area of 50 m2. Cultivation of need for reliable truffle cultivation techniques be- T. aestivum has been developed in France and Italy came obvious. In the late 1960s and 1970s, success- (Chevalier & Frochot, 1987, 1989, 1997b, 2002; ful production of Tuber mycorrhizae in greenhouse Chevalier & Dupre´, 1988; Giovanetti et al., 1994; experiments was demonstrated (Fontana, 1967; Belloli et al., 2001). Because of an ongoing decline Palenzona, 1969; Fontana & Bonfante-Fasolo, of oaks in Sweden since the 1700s (Sta˚a˚l, 1994; 1971; Grente et al., 1972; Chevalier & Desmas, L. Kardell, Swedish University of Agricultural 1975; Delmas & Poitou, 1979). In 1976, the first Sciences, personal communication), associated truffles (T. melanosporum) were produced in a truffle fauna and flora are becoming rare, making econom- orchard (truffie`re) of inoculated seedlings in Italy, ical incentives for planting oak an important goal per 6 years after planting (G. Chevalier, French National se. A 5-year research project was therefore estab- Institute for Agricultural Research, personal com- lished in 1999 to study natural populations of munication). In 1977 the first truffles (T. melanos- T. aestivum on Gotland, seedling inoculation techni- porum) from inoculated seedlings were produced in ques and truffle cultivation in Sweden with the France, 3.5 years after planting (Chevalier & Grente, overall aim of causing socioeconomic effects, parti- 1979). Seedling inoculation has also made it possible cularly on the rural island of Gotland (Figure 1). to establish productive truffle orchards outside the Truffles have historically been collected in the natural geographical distribution of these truffles, wild, but Joseph Talon discovered in the early 1800s e.g. in New Zealand and North America (Hall et al., that planting acorns in natural truffle regions could 1998a; Hall & Wang, 2002). Currently, commercial mycorrhizal truffle seed- 10°E 15°E 20°E 25°E lings are produced using mainly T. melanosporum (black Pe´rigord truffle) and T. aestivum (black Burgundy truffle) (Chevalier & Frochot, 1987, 1989; Hall et al., 1998b). Because of the commercial value of successful inoculation techniques, large truffle seedling producers guard their methods well (Hall et al., 2003, 2007). However, successful Sweden inoculations of numerous host species with various 60°N 60°N Tuber species have been reported (Table I). Table II lists the reported mycorrhiza synthesis of T. aestivum Gotland with different plant species and inoculation methods. Roots of an ectomycorrhizae-forming tree or plant can be inoculated with an ectomycorrhizal fungus by contact with germinating spores, mycelia or mycor- rhizae. Pieces of a root system, or an entire plant 55°N 55°N with mycorrhizae, could be potted together with the seedlings to be inoculated (Chevalier & Grente, 1973). Mycorrhizae may develop on the new seed- 10°E 15°E 20°E 25°E lings within 2Á3 months and the method is applic- Figure 1. Map of southern Scandinavia showing the position of able to many Tuber species (Giovanetti et al., 1994). the Swedish island of Gotland, off the Swedish east coast. Mycelial inoculation requires truffle mycelium ob- (Illustration: Anders Larsson.) tained in pure culture on artificial substrate. Such 40 C. Wede´n et al. Table I. Reported mycorrhiza synthesis of Tuber species. Tuber sp. References Tuber aestivum Palenzona (1969), Chevalier et al. (1973, 1975), Chevalier & Desmas (1975), Giovannetti & Fontana (1982), Zambonelli & Branzanti (1984), Zambonelli & Govi (1988), Zambonelli et al. (1993), 1995), Donnini et al. (2003), Pruett et al. (2008) Tuber borchii Fassi & Fontana (1967), Fontana (1967), Fontana & Palenzona (1969), Fontana & Bonfante- Fasolo (1971), Giovannetti & Fontana (1982), Zambonelli & Branzanti (1984), 1989), Zambonelli et al. (1993), 1995, 2002), Granetti et al. (1995), Sisti et al. (1998), Giomaro et al. (2000) Tuber brumale Palenzona (1969), Palenzona et al. (1972), Chevalier (1973), Chevalier