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Factors affecting yield of Tuber melanosporum in a Quercus ilex plantation in southern France
1176
Mycol. Res. 100 (10): 1176-1178 (1996) Prblfed in Great Britairr
Factors affecting yield of Tuber melanosporum in a Quercus ilex plantation in southern France
P. J. A. SHAW1, K. LANKEY1 A N D A. J O U R D A N 2
' Soaithbnds College, Roehanlpton Institute, Winzbledon Parkside, London SW19 5NN,U.K. 2Associatio~Tr~ificulturedu Canton de Lambesc et Environs, B.P. 26 a 13840, Rognes, Prozlence, France
Yields of Tuber nielanosporurn 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.
Truffles are hypogeous fruit bodies of ectomycorrhizal fungi, which depend on animals to excavate and consume the sporophore for spore dispersal (Maser, Trappe & Nussbaum, 1978; Pacioni, 1989). A few species are highly prized by humans as a food flavouring, of which the best known is the highly valued PCrigord truffle Tuber melanosporum Vittad. (Ramsbottom, 1953; Ducharel, 1993; Shaw 1995). Although truffles are still harvested from the wild, most European truffles are believed to come from cultivated sources (although it is impossible to be sure, since no official records are kept of truffle production). Like most ectomycorrhizal fungi, truffles do not fruit in axenic culture and can currently only be harvested by inoculating suitable host trees and waiting for fruit body production. There is a large body of knowledge built up by truffle growers, but which remains largely outside the conventional mycological literature (Shaw, 1995). Recently, Hall, Brown & Byars (1994) have produced a book
MATERIALS A N D M E T H O D S Work was undertaken at the Chemin du Jas Blanc, near the village of Rognes, Provence, France (3' 35' E, 48' 50' N) on an alluvial sandy soil. The site is unshaded and approximately flat, with an area of 1.0 ha. Prior to planting the land was a vineyard. In 1977 the site was cleared, ploughed and planted with saplings of evergreen oak Quercus ilex L. whose roots had been treated with a commercial Tuber melanosporum inoculum. Trees were planted in a 27 x 25 rectangular grid system at 2 m spacing. Due to some losses and incomplete planting, the site contained a total of 461 specimens of Q . ilex. Truffle hunts are undertaken during autumn using trained dogs, whose efficiency has been proved in contests involving buried truffles (Shaw, 1995). The only management applied to the trees was irrigation by fixed pipes during dry weather, and clipping of the lower branches under trees where truffles had been located to facilitate excavation. Records were kept of the presence/ absence of truffles under each tree for each year.
.,
Fig. 1. Annual trends in the percentage of Quercw ilex trees
producing truffles in the Chemin du Jas Blanc plantation. Trees were Total trees that have produced so far; established in 1977. total trees producing this year; 0, trees started production this year.
+,
which included a compilation of trufficultural techniques, aimed primarily at southern hemisphere cultivation. The work described below concerns a French truffle plantation where records have been kept of the precise location of each truffle-producing tree in each year since planting. Preliminary examination of the data showed considerable variation between trees in truffle production, with a zone of good production through the middle of the site (Shaw, 1995). A study was undertaken to investigate environmental factors that might contribute to this variation. Factors chosen were soil chemistry and tree size, as both have been found to be related to the development of ectomycorrhizal fruit body successions (Last, Dighton & Mason, 1987; Shaw & Lankey, 1994).
P. J. A. Shaw, K. Lankey and A. Jourdan O n 21 April 1995 soil samples and basal diameter measurements were taken from a stratified random sample of 47 trees. The sampling was from two trees per row, except for three rows where a combination of geometry and poor establishment led to fewer than five usable trees, in which case only one was sampled. Four soil samples (3 cm depth) were taken from each of the sampled trees (50 cm north, south, east and west of the trunk) and pooled for analyses. pH was measured using 10 g fresh soil in 25 ml distilled water. Phosphate-phosphorus extraction used Olsen's method (Allen, 1974) and its determination followed Murphy & Riley (1962). Organic matter was expressed as percentage loss on ignition after 2 h at 400 OC. Potassium was determined by atomic absorption spectrophotometry after ashed materials were extracted in ammonium acetate solution buffered to pH 9 (Allen, 1974).
RESULTS A N D DISCUSSION Mean basal diam. (10 cm above ground level) of the trees was 14.1 cm (s.D. = 4.2 cm). Height was not measured since diameter is considered to be a better indicator of biomass (Rutter, 1955), but no trees exceeded 4 m. Mean values for soil parameters ( f s.D.) are: P 1.14f 0.57 mg 100 g l , K 24.00 f 7.62 mg 100 g-l, pH 7.75 f0.25, LO1 3.04 f 0.88%. All truffles excavated were found to be Tuber melanosporum, except for one tree which produced Tuber brumale Vittad. Truffle production started in 1987, 10 yr after planting, when truffles were found under 47 trees (10.2%). Figure 1 shows that the number of trees producing truffles each year increased steadily, except for a dip in 1989. It also shows for each year the number of trees producing truffles for the first time (which varied erratically between 2 and lo%), and the total number of trees that had produced up to that year. Many trees had one or more fallow years after first yielding truffles. Although 47 trees produced truffles in 1987, only 7 of these produced a harvest in every subsequent year. Rainfall data for Marseille were examined for the period 1987-91 (Weatherdisc Associates Ltd, 1995), and showed an unusually dry spring in 1989 followed by a dry winter. These could explain the production dip during 1989, but the data are too limited to allow detailed analysis. The harvest data for each tree consisted of boolean variables (i.e. 1 or 0 for each year) rather than actual yields, necessitating non-parametric statistical analyses. Truffle production was calculated as the unweighted sum of each year's boolean value (i.e. the number of years in which each tree yielded truffles) for each tree. This means that a tree which produced truffles in any 6 yr out of 8 would be given a score of 6. This approach implicitly treats truffle production in 1987 as being equally important as production in 1994. This calculation was repeated with each year weighted so that early fruiting resulted in a relatively higher score, but the resulting analyses gave identical results to unweighted scores so have been excluded from further discussion. The best predictor of truffle yield was found to be basal diameter (r, = 0.58, D.F.= 45, P < 0.01). No soil variables were correlated with truffle yield, although potassium was significantly correlated with basal diameter (rs = 0.33, D.F.=
1177 45, P < 0.05). There were only two other significant correlations; soil pH with potassium (r, = 0.44, D.F. = 45, P < 0.01) and soil pH with phosphorus (r, = 0.54, D.F.= 45, P < 0.01). A 1-way ANOVA was performed on all parameters using presence/absence of truffles at any stage as the classification variable. Thus all trees whose score was 0 were in one category, all trees with scores > 0 were in the other. The only parameter to differ significantly between categories was basal diameter, with a mean ( fs.D.) of 11.8 f 4.1 cm for nonproducing trees and 15.5 3.7 cm for truffle-producing trees (P < 0.01). The data above are unusual in that they cover a hypogeous fruit body succession. Fruit body successions above ground are well documented for ectomycorrhizal fungi (Deacon, Donaldson & Last, 1983; Last et al., 1984; Mason, Wilson & Last, 1984; Dighton, Poskitt & Howard, 1986; Last, Dighton & Mason 1987; Shaw & Lankey, 1994), but very little equivalent work has been performed on hypogeous fungi due to the difficulty of locating them (Fogel, 1981). Previous work on such successions has tended to link successional development to tree maturity (Dighton & Mason, 1985). However it is recognized that soil chemistry can also play a role in determining the appearance of late stage fungi. Last et al. (1987) noted that late stage fungi generally tend to be associated with high levels of soil organic matter, while Shaw & Lankey (1994) found that elevated soil phosphate retarded a fruit body succession. The data above show that, for the Tuber melanosporurn/Quercus ilex symbiosis at tree maturity, the critical factor defining fruit body production was stem diameter. The lack of any relationships between truffle production and soil chemistry may simply reflect a shortage of data, although the soil sampling covered 1 0 % of the trees in the plantation. Alternatively other unmeasured edaphic factors such as subsoil composition or hydrology may have acted as tree growth determinants. -
-
Thanks are due to Jean and Elinor Neubert for linguistic assistance. Mary Mackenzie produced the figure.
REFERENCES Allen, S. E. (1974). The Chemical Analysis of Ecological Materials. Blackwell: Oxford. Deacon, J. W., Donaldson, S. J. & Last, F. T. (1983). Sequences and interactions of mycorrhizal fungi on birch. Plant and Soil 71, 257-262. Dighton, J. & Mason, P. A. (1985). Mycorrhizal dynamics during forest tree development. In Developmental Biology of Higher Fungi (ed. D. Moore, L. A. Casselton, D. A. Wood & J. C. Frankland), pp. 117-139. Cambridge University Press: Cambridge, U.K. Dighton. J., Poskitt, J. M. & Howard, D. M. (1986). Changes in the occurrence of basidiomycete fruit bodies during forest stand development: with specific reference to mycorrhizal species. Transactions of the British Mycological Society 87, 163-171. Ducharel, M. (1993). The food of love7 Mycologist 7(1), 25-27. Fogel, R. (1981). Quantification of sporocarps produced by hypogeous fungi. In nle Fungal Community, its Organisation and Role in the Ecosystem (ed. D. T. Wicklow & G. C. Carroll), pp. 553-568. Marcel Dekker: New York, USA. Hall, I., Brown, G. & Byars, J. (1994). The Black Truffle, its History, Uses and Cultivation. New Zealand Institute for Crop and Food Research Ltd: New Zealand.
Yields of Tuber melanosporum Last, F. T., Dighton, J. & Mason, P. A. (1987). Successions of sheathing mycorrhizal fungi. Trends in Ecology and Evolution 2, 157-161. Last, F. T., Mason, P. A,, Ingleby, K. & Fleming, L. V. (1984). Succession of fruitbodies of sheathing mycorrhizal fungi associated with Betula pendula. Forest Ecology and Management 9, 229-234. Maser, C.. Trappe, J. M. & Nussbaum, P. A. (1978). Fungus-small mammal interrelationships with emphasis on Oregon coniferous forests. Ecology 59, 799-809. Mason, P. A., Wilson, I. & Last, F. T. (1984). Mycomhizal fungi of Betula spp.: factors affecting their occurrence. Proceedings of the Royal Society of Edinburgh 85B. 141-151. Murphy, J. & Riley, J. P. (1962). A modified single solution method for the
(Accepted 23 February 1996)
1178 determination of phosphate in natural waters. Analytica Chimica Acta 26, 31-36. Pacioni, G. (1989). Biology and ecology of truffles. Acta Mediterraneum Romani 27, 104-117. Ramsbottom, J. (1953). Mushroo~nsand Toadstools. Collins: London. Rutter, A. J. (1955). The relationship between dry weight increase and linear measures of growth in young conifers. Forestry 28, 125-135. Shaw, P. J. A. (1995). Mycological Societies: Association Trufficulture du Canton de Larnbesc et Environs. Mycologist 9, 115-116. Shaw, P. J. A. & Lankey, K. (1994). Studies on the Scots pine mycorrhizal fruitbody succession. Mycologist 8, 172-175. Weatherdisc Associates Ltd (1995). World Weather Disc CD ROM.
Mycol. Res. 100 (10): 1176-1178 (1996) Prblfed in Great Britairr
Factors affecting yield of Tuber melanosporum in a Quercus ilex plantation in southern France
P. J. A. SHAW1, K. LANKEY1 A N D A. J O U R D A N 2
' Soaithbnds College, Roehanlpton Institute, Winzbledon Parkside, London SW19 5NN,U.K. 2Associatio~Tr~ificulturedu Canton de Lambesc et Environs, B.P. 26 a 13840, Rognes, Prozlence, France
Yields of Tuber nielanosporurn 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.
Truffles are hypogeous fruit bodies of ectomycorrhizal fungi, which depend on animals to excavate and consume the sporophore for spore dispersal (Maser, Trappe & Nussbaum, 1978; Pacioni, 1989). A few species are highly prized by humans as a food flavouring, of which the best known is the highly valued PCrigord truffle Tuber melanosporum Vittad. (Ramsbottom, 1953; Ducharel, 1993; Shaw 1995). Although truffles are still harvested from the wild, most European truffles are believed to come from cultivated sources (although it is impossible to be sure, since no official records are kept of truffle production). Like most ectomycorrhizal fungi, truffles do not fruit in axenic culture and can currently only be harvested by inoculating suitable host trees and waiting for fruit body production. There is a large body of knowledge built up by truffle growers, but which remains largely outside the conventional mycological literature (Shaw, 1995). Recently, Hall, Brown & Byars (1994) have produced a book
MATERIALS A N D M E T H O D S Work was undertaken at the Chemin du Jas Blanc, near the village of Rognes, Provence, France (3' 35' E, 48' 50' N) on an alluvial sandy soil. The site is unshaded and approximately flat, with an area of 1.0 ha. Prior to planting the land was a vineyard. In 1977 the site was cleared, ploughed and planted with saplings of evergreen oak Quercus ilex L. whose roots had been treated with a commercial Tuber melanosporum inoculum. Trees were planted in a 27 x 25 rectangular grid system at 2 m spacing. Due to some losses and incomplete planting, the site contained a total of 461 specimens of Q . ilex. Truffle hunts are undertaken during autumn using trained dogs, whose efficiency has been proved in contests involving buried truffles (Shaw, 1995). The only management applied to the trees was irrigation by fixed pipes during dry weather, and clipping of the lower branches under trees where truffles had been located to facilitate excavation. Records were kept of the presence/ absence of truffles under each tree for each year.
.,
Fig. 1. Annual trends in the percentage of Quercw ilex trees
producing truffles in the Chemin du Jas Blanc plantation. Trees were Total trees that have produced so far; established in 1977. total trees producing this year; 0, trees started production this year.
+,
which included a compilation of trufficultural techniques, aimed primarily at southern hemisphere cultivation. The work described below concerns a French truffle plantation where records have been kept of the precise location of each truffle-producing tree in each year since planting. Preliminary examination of the data showed considerable variation between trees in truffle production, with a zone of good production through the middle of the site (Shaw, 1995). A study was undertaken to investigate environmental factors that might contribute to this variation. Factors chosen were soil chemistry and tree size, as both have been found to be related to the development of ectomycorrhizal fruit body successions (Last, Dighton & Mason, 1987; Shaw & Lankey, 1994).
P. J. A. Shaw, K. Lankey and A. Jourdan O n 21 April 1995 soil samples and basal diameter measurements were taken from a stratified random sample of 47 trees. The sampling was from two trees per row, except for three rows where a combination of geometry and poor establishment led to fewer than five usable trees, in which case only one was sampled. Four soil samples (3 cm depth) were taken from each of the sampled trees (50 cm north, south, east and west of the trunk) and pooled for analyses. pH was measured using 10 g fresh soil in 25 ml distilled water. Phosphate-phosphorus extraction used Olsen's method (Allen, 1974) and its determination followed Murphy & Riley (1962). Organic matter was expressed as percentage loss on ignition after 2 h at 400 OC. Potassium was determined by atomic absorption spectrophotometry after ashed materials were extracted in ammonium acetate solution buffered to pH 9 (Allen, 1974).
RESULTS A N D DISCUSSION Mean basal diam. (10 cm above ground level) of the trees was 14.1 cm (s.D. = 4.2 cm). Height was not measured since diameter is considered to be a better indicator of biomass (Rutter, 1955), but no trees exceeded 4 m. Mean values for soil parameters ( f s.D.) are: P 1.14f 0.57 mg 100 g l , K 24.00 f 7.62 mg 100 g-l, pH 7.75 f0.25, LO1 3.04 f 0.88%. All truffles excavated were found to be Tuber melanosporum, except for one tree which produced Tuber brumale Vittad. Truffle production started in 1987, 10 yr after planting, when truffles were found under 47 trees (10.2%). Figure 1 shows that the number of trees producing truffles each year increased steadily, except for a dip in 1989. It also shows for each year the number of trees producing truffles for the first time (which varied erratically between 2 and lo%), and the total number of trees that had produced up to that year. Many trees had one or more fallow years after first yielding truffles. Although 47 trees produced truffles in 1987, only 7 of these produced a harvest in every subsequent year. Rainfall data for Marseille were examined for the period 1987-91 (Weatherdisc Associates Ltd, 1995), and showed an unusually dry spring in 1989 followed by a dry winter. These could explain the production dip during 1989, but the data are too limited to allow detailed analysis. The harvest data for each tree consisted of boolean variables (i.e. 1 or 0 for each year) rather than actual yields, necessitating non-parametric statistical analyses. Truffle production was calculated as the unweighted sum of each year's boolean value (i.e. the number of years in which each tree yielded truffles) for each tree. This means that a tree which produced truffles in any 6 yr out of 8 would be given a score of 6. This approach implicitly treats truffle production in 1987 as being equally important as production in 1994. This calculation was repeated with each year weighted so that early fruiting resulted in a relatively higher score, but the resulting analyses gave identical results to unweighted scores so have been excluded from further discussion. The best predictor of truffle yield was found to be basal diameter (r, = 0.58, D.F.= 45, P < 0.01). No soil variables were correlated with truffle yield, although potassium was significantly correlated with basal diameter (rs = 0.33, D.F.=
1177 45, P < 0.05). There were only two other significant correlations; soil pH with potassium (r, = 0.44, D.F. = 45, P < 0.01) and soil pH with phosphorus (r, = 0.54, D.F.= 45, P < 0.01). A 1-way ANOVA was performed on all parameters using presence/absence of truffles at any stage as the classification variable. Thus all trees whose score was 0 were in one category, all trees with scores > 0 were in the other. The only parameter to differ significantly between categories was basal diameter, with a mean ( fs.D.) of 11.8 f 4.1 cm for nonproducing trees and 15.5 3.7 cm for truffle-producing trees (P < 0.01). The data above are unusual in that they cover a hypogeous fruit body succession. Fruit body successions above ground are well documented for ectomycorrhizal fungi (Deacon, Donaldson & Last, 1983; Last et al., 1984; Mason, Wilson & Last, 1984; Dighton, Poskitt & Howard, 1986; Last, Dighton & Mason 1987; Shaw & Lankey, 1994), but very little equivalent work has been performed on hypogeous fungi due to the difficulty of locating them (Fogel, 1981). Previous work on such successions has tended to link successional development to tree maturity (Dighton & Mason, 1985). However it is recognized that soil chemistry can also play a role in determining the appearance of late stage fungi. Last et al. (1987) noted that late stage fungi generally tend to be associated with high levels of soil organic matter, while Shaw & Lankey (1994) found that elevated soil phosphate retarded a fruit body succession. The data above show that, for the Tuber melanosporurn/Quercus ilex symbiosis at tree maturity, the critical factor defining fruit body production was stem diameter. The lack of any relationships between truffle production and soil chemistry may simply reflect a shortage of data, although the soil sampling covered 1 0 % of the trees in the plantation. Alternatively other unmeasured edaphic factors such as subsoil composition or hydrology may have acted as tree growth determinants. -
-
Thanks are due to Jean and Elinor Neubert for linguistic assistance. Mary Mackenzie produced the figure.
REFERENCES Allen, S. E. (1974). The Chemical Analysis of Ecological Materials. Blackwell: Oxford. Deacon, J. W., Donaldson, S. J. & Last, F. T. (1983). Sequences and interactions of mycorrhizal fungi on birch. Plant and Soil 71, 257-262. Dighton, J. & Mason, P. A. (1985). Mycorrhizal dynamics during forest tree development. In Developmental Biology of Higher Fungi (ed. D. Moore, L. A. Casselton, D. A. Wood & J. C. Frankland), pp. 117-139. Cambridge University Press: Cambridge, U.K. Dighton. J., Poskitt, J. M. & Howard, D. M. (1986). Changes in the occurrence of basidiomycete fruit bodies during forest stand development: with specific reference to mycorrhizal species. Transactions of the British Mycological Society 87, 163-171. Ducharel, M. (1993). The food of love7 Mycologist 7(1), 25-27. Fogel, R. (1981). Quantification of sporocarps produced by hypogeous fungi. In nle Fungal Community, its Organisation and Role in the Ecosystem (ed. D. T. Wicklow & G. C. Carroll), pp. 553-568. Marcel Dekker: New York, USA. Hall, I., Brown, G. & Byars, J. (1994). The Black Truffle, its History, Uses and Cultivation. New Zealand Institute for Crop and Food Research Ltd: New Zealand.
Yields of Tuber melanosporum Last, F. T., Dighton, J. & Mason, P. A. (1987). Successions of sheathing mycorrhizal fungi. Trends in Ecology and Evolution 2, 157-161. Last, F. T., Mason, P. A,, Ingleby, K. & Fleming, L. V. (1984). Succession of fruitbodies of sheathing mycorrhizal fungi associated with Betula pendula. Forest Ecology and Management 9, 229-234. Maser, C.. Trappe, J. M. & Nussbaum, P. A. (1978). Fungus-small mammal interrelationships with emphasis on Oregon coniferous forests. Ecology 59, 799-809. Mason, P. A., Wilson, I. & Last, F. T. (1984). Mycomhizal fungi of Betula spp.: factors affecting their occurrence. Proceedings of the Royal Society of Edinburgh 85B. 141-151. Murphy, J. & Riley, J. P. (1962). A modified single solution method for the
(Accepted 23 February 1996)
1178 determination of phosphate in natural waters. Analytica Chimica Acta 26, 31-36. Pacioni, G. (1989). Biology and ecology of truffles. Acta Mediterraneum Romani 27, 104-117. Ramsbottom, J. (1953). Mushroo~nsand Toadstools. Collins: London. Rutter, A. J. (1955). The relationship between dry weight increase and linear measures of growth in young conifers. Forestry 28, 125-135. Shaw, P. J. A. (1995). Mycological Societies: Association Trufficulture du Canton de Larnbesc et Environs. Mycologist 9, 115-116. Shaw, P. J. A. & Lankey, K. (1994). Studies on the Scots pine mycorrhizal fruitbody succession. Mycologist 8, 172-175. Weatherdisc Associates Ltd (1995). World Weather Disc CD ROM.