In vitro synthesis of ectomycorrhizas on Casuarinaceae with a range of mycorrhizal fungi

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1 New Phytol. (1991), 118, In vitro synthesis of ectomycorrhizas on Casuarinaceae with a range of mycorrhizal fungi BY COSTAS THEODOROU' AND PAUL REDDELL ^ CSIRO, Division of Soils, Private Bag No. 2, Glen Osmond, S.A. 564, Australia " CSIRO, Division of Soils, Private Bag, Aitkenvale, Qld 4814, Australia {Received 26 June 199; accepted 3 January 1991) SUMMARY Eleven species of mycorrhizal fungi, selected from stands of either Eucalyptus spp., Allocasuarina spp, or Pinus radiata D, Don were tested in an aseptic system for their abilities to initiate ectomycorrbiza with Allocasuarina littoratis (Salisb,) L. Johnson, Casuarina equisetijolia ssp. equisetifolia L, and C cunninghamiana Miq, Elaphumyces sp., Hysterangium sp,, Laecaria laecata (Scop ex Fr,) Bk, & Br., Pisolithus tinctortus (Pers.) Coker & Couch, Scleroderma sp. and Thelephora terrestris (Ehrh.) Fr. formed ectomycorrhizas on all three bosts, Amanita sp, fornned ectomycorrbizas on A. littoralis and C, curininghamiana but not on C. equisetifolia. Paxilltts involutus (Batch ex Fr.) Fr. formed ectomycorrhizas on A. littoralis only, P. tinctorius also formed ectomycorrbizas with C. obesa Miq. Rhizopogov luteolus Fr. & Nord, Suillus granulatus (L, ex Fr,) Kuntze and S. piperatus (Bull ex Fr,) O, Kuntze colonized the rhi/.ospbere of Casuarinaceae but did not form ectomycorrbizas. The comparative intensity of ectomycorrhizal infection by P. tinctorius and L. laecata was assessed on four host species. Infection intensity ranged from 13 to 7'V, of laterals infected and decreased for both fungal species in the order: A. littoralis > Eucalyptus pilularis Smith > C. equisetifolia > C. cunninghamiana. An exogenous supply of glucose induced greater and sometimes earlier, ectomycorrhizal infection of A. littoralis, C. equisetifolia and C. cunninghamiana by P. tinctorms and /.., laecata tban tbat in the absence of giucose. Tbe optimum glucose level for tbese fungi and bosts in tbis synthesis system was 75/^g glucose (g soil)"'. Key words: Ectomycorrbiza, Casuarina, Allocasuarina, Eucalyptus, intensity of infection. INTRODUCTION Members of Casuarinaceae occur naturally m a wide range of environments from arid woodlands to tropical forests (Barlow% 1983). They are valued as nitrogen fixing trees in many tropical countries, and are used for fuelwood production, land reclamation and windbreaks (Midgley, Turnbull & Johnston, 1983). Casuarinaceae are reported to form both ectomycorrhizal (Trappe, 1962) and VA mycorrhizal associations (Diem & Gauthier, 1982). Reddell, Bowen & Robson (1986) observed that ectomycorrhizas were found more frequently on Allocasuarina than on Casuarina, the reverse was true for VA mycorrhiza. Both types of mycorrhiza were sometimes found on the same plant. However, the ecological importance of these associations and the possibilities for improving performance in plantations by inoculation with selected beneficial fungi have not been addressed. There is little information as to the identity of the symbiotic fungi involved in ectomycorrhizal infection of Casuarinaceae. As far as we are aware there has only been one published study, which reported synthesis of ectomycorrhizas on Casuarina equisetifolia and PisoUthus tinctorius (Ba, Sougoufara & Thoen, 1987), Here we describe a method for aseptically synthesizing ectomycorrhizas by inoculating seedlings of Casuarinaceae with either pure cultures or spores of known ectomycorrhizal fungi. Using this system we have: (i) determined the potential abilities of eleven fungi to form ectomycorrhizas with species from two genera of Casuarinaceae Casuarina and Allocasuarina, (ii) assessed the intensity of ectomycorrhizal infection by two of these fungi on different host species, and (iii) examined the effects of exogenously supplied glucose on the extent of mycorrhizal infection.

2 28 C. Theodorou and P. Reddell MATERIALS AND METHODS Description of in vitro synthesis technique All fungi used in these experiments were isolated on MelinNorkrans medium (Melin, 1959) from fructifications collected under stands of Eucalyptus, Allocasuarina and Pinus in Australia (Table 1) and were species which have been reported to initiate ectomycorrhizas on forest trees (Trappe 1962; Malajczuk, iviolina & Trappe, 1982). The technique for synthesis of ectomycorrhizas on Casuarinaceae was modified from that commonly used for other ectomycorrhizal hosts (Molina & Palmer, 1982). Syntheses were performed in autoclavable, polypropylene screwtop tubes of 12 ml capacitt,. The soil was a Typic Quartzipsamment (Soil Survey Staff, 1975) collected from a Casuarina cristata F. Muell. ex. Miq. stand. This siliceous sand (89'^ coarse sand, 11 "^ fine sand, ph 72) was low in organic matter and deficient in phosphorus [< l/(g (g bicarbonate extractable phosphorus)'^] and in most other plant nutrients. Eighty f^rams were weighed into each tube, moistened with 15 g water (g airdry soil)"^ and then the tubes were autocla\ ed for 2min at 121 C. Seeds were surface sterilized for 3 min in a 5:5 mixture of SO",, alcohol and 2 vol H^O^, washed with five changes of sterile distilled water and transferred aseptically to glucoseyeastpeptone agar (Rovira, 1959). Following germination, seedlings with roots about \ cm long were selected from plates free of contaminants and planted into the tubes of sterilized soil. Each tube had previously been inoculated with a 4 mm diameter disc from the perimeter of an actively grow ing fungal culture on MelinNorkrans medium. The inoculum was placed 2 cm below the soil surface, covered with the sterile soil and the seedling was planted immediately with the root placed on top of the inoculum. The inoculated plants were grown wholly enclosed in the tightly sealed tubes. In the case of P. tinctorius, basidiospores were also used as inoculum by mixing '2 ml of an axenic spore suspension containing 2 X 1' spores ml"' into the soil and also by dipping the root in the spore suspension before planting. Experiment ): specificity in the Casuarinaceae Fleven ectomycorrhizal fungi were tested for their abilities to initiate ectomycorrhizas with three species of Casuarina (C. equisetifolia, C. cunninghamiana, C obesa) and with Allocasuarina littoralis. Four replicates were used for each fungushost combination. Details of the combinations examined are presented in Table 2. The inoculated plants were grown in a glasshouse for 12 wk at a 912 h day at 2633 C and 1512 h night at 116 C. At harvest the roots were washed gently to remove adhering sand particles and were then examined under a dissecting microscope at x 4 magnification. Roots were considered ectomycorrhizal when there was a hyphal mantle, root hairs were absent and the roots had a generally swollen appearance. Where there was doubt, infection was confirmed by microscopic examination of crosssections. Putative ectomycorrhizal roots were stored in formaldehydeacetic acidalcohol (FAA), dehydrated through a graded alcohol series and embedded in Spurr's resin. Sections between 15 and 25 //m thick were stained w^ith 1 "o toluidine blue in 1 "o borax and examined for the presence of a sheath and Hartig net. Experiment 2: intensity of infection on different tree species Seedlings of four tree species (A. littoralis, C. equisetifolia, C. cunninghamiana and Eucalyptus pilularis) were used in this experiment. Axenically germinated seedlings were raised as in expt 1, inoculated with mycelial cultures of either P. tinctorius or L. laccata and grown for 16 wk in the glasshouse. The intensity of infection was expressed as the percentage of lateral roots per seedling which had become mycorrhizal as indicated by the presence of a fungal mantle and analysed statistically after arcsin transformation. Experiment 3: effect of exogenous supply of glucose on ectomycorrhizal infection Ectomycorrhizal infection on roots of seedlings of Casuarina spp. is often not evident before 6 wk after inoculation. This experiment investigated the possibility of using an exogenous supply of glucose to increase fungal colonization of the root and hasten the initiation of mycorrhizas. The method for synthesis of ectomycorrhizas was as described above with one modification. Instead of moistening the soil with water, solutions containing either, 125, 25, 5, 1 and 2",, glucose at the rate of '15 ml solution (g airdry soil)"^ were used. Axenically raised seedlings of A. littoralis, C. equisetifolia and C. cunninghamiana were planted in soil inoculated with P. tinctorius and L. laccata as above. The seedlings w^re placed in the glasshouse and harvested serially at 4, 6 and 8 wk from transplanting. The length of root colonized by the inoculated fungus was measured under a dissecting microscope (x 4 magnification) using reflected light. Comparative intensity of colonization at the region of greatest fungal growth was recorded as light, moderate, heavy or very heavy. The numbers of ectomycorrhizas and uninfected laterals were counted under the dissecting microscope. The intensity of infection was expressed as the percentage

3 Ectomycorrhizas of Casuarinaceae Table 1. Fungi tested in pure culture synthesis for ectomycorrhiza formation on Casuarina spp. and Allocasuarina spp. Fungus Collection locations Putative hosts Amanita sp, Blaphomyces sp, Hysterangium sp, Laeearia laecata (Scop ex Fr,) Bk. & Br. Paxillus involutus (Batcb ex Fr,) Fr, Pisolithus tinetorius (Pers,) Coker & Couch Rhizopogon luteolus Fr, and Nord Scleroderma sp, Suillus granulatus (L, ex Fr.) Kuntze S. piperatus (Bull, ex Fr.) O, Kuntze Thelephora terrestris (Enrh.) Fr. Mt Magnificent, S.A, Cooloola, Qld Mt Crawford, S.A. Dwellingup, W.A. Mt Bonython, S.A. Rosedale, N.S.W. Mt Gambier, S, A. Urrbrae, S.A, Mt Gambier, S.A, Kuitpo, S.A, Kuitpo, S,A, Allocasuarina spp, Allocasuarina littoralis Euealyptus spp., A. z^erticillata Euealyptus spp. Eucalyptus spp, Allocasuarina littoralis Pinus radiata Eucalyptus spp. Pinus radial a Pinus radiata Pinus radiata Table 2. Mycorrhisal infection of Casuarinaceae by different fungi 12 wk after inoculation Host Inoculated fungus Allocasuarina littoralis Casuarina equisetifolia Casuarina cunninghamiana Casuarina obesa Amanita sp Elaphomyees sp. Hysterangium sp. Laeearia laecata Paxillus involutus Pisolithus tinctorius Mycelium Basidiospores Scleroderma sp. Thelephora terrestris Rhisopogon luteolus Suillus granulatus S. piperatus 1 h n.a. n.a. n.a. I n.a. n.a. 1 n.a. n.a. n.a. n.a. n.a. n.a. Mycorrhizas present in all four replicates; Mycorrhizas absent in all four replicates. n.a., Synthesis not attempted. of laterals which were mycorrhizal and analysed statisticallv after arcsin transformation. RESULTS AND DISCUSSION Specificity Ectomycorrhizal infections arising from the 34 hostfungus combinations that were made are given in Table 2. The distinctive morphological characteristics of these ectomycorrhizas are summarized in Table 3. In the case of Allocasuarina littoralis the Hartig net penetrated between the epidermis and the next layer of cells and sometimes even deeper and the surrounded host cells were radially expanded. The Casuarina spp. showed variation in the Hartig net formation. It usually surrounded the epidermal cells only but in some cases there was no Hartig net penetration. In the Casuarina species the cells were not radially expanded. For each fungus our descriptions are similar to those reported by other authors with other compatible hosts (P. tinctorius on Eucalyptus, Malajczuk, Molina & Trappe, 1982: Amanita muscaria (L. ex Fr.) Pers. ex Hooker on Eucalyptus, Matajczuk et al., 1984: Laecaria laecata and Hysterangium sp. on Eucalyptus, Malajczuk, Dell & Bougher, 1987 : T. terrestris on shortleaf pine, Marx & Davey, 1969: P. involutus and Scleroderma sp. on red alder, Molina, 1979; 1981), Molina (1979, 1981) reported that P. involutus mycorrhizas on Alnus were creamwhite changing to golden brown with age. The white colour of P. involutus mycorrhizas in our studies was probably because they were young and not yet pigmented. The Elaphomyees sp, exhibited some intracellular infection of cortical cells. This genus is considered to have an affinity w^ith Cenoeoccum geophilum which may be its imperfect stage (Trappe, 1971). Although C. geophilum and Elaphomyees were ectomycorrhizal

4 282 C. Theodorou and P. Reddell Table 3. General morphological characteristics of ectomycorrhizas formed in vitro on Casuarinaceae Mantle Fungus Structure Root apex enclosed Hartig net Intracellular infection Pisolithus tinctorius Laccaria laccata Elaphomyces sp. Scleroderma sp. Thelephora terrestris Amanita sp. Hysterangium sp. Paxillus involutus Rhizopogon luteolus Suillus granulatus Suillus piperatus Compact close to epidermis Outer layers loose Compact close to epidermis Outer layers loose Compact close to epidermis Outer layers loose Compact Compact Compact Loose Compact close to epidermis Outer layers loose Absent Absent Absent Always Usually Usually Always Never Usually Never Never Table 4. Intensity of infection of Allocasuarina littoralis, Casuarina equisetifolia, Casuarina cunnmghamiana and Eucalyptus pilularis by Pisolithus tinctorius and Laccaria laccata. Plants grown for 16 wk in a glasshouse Fungus Plant P. tinctorius A. littoralis C. equisetifolia C. cunninghamiana E. pilularis L. laccata A. littoralis C. equisetifolia C. cunninghamiana E. pilularis L'ninoculated A. littoralis C. equisetifolia C. cunninghamiana E. pilularis Number of mycorrhizas* Total number of laterals* Mycorrhiza*t (^.) 7 a 37 b 29b 56c 28 a 19bc 13c 22ab LSD for comparing effect of fungus on production of laterals by eacb bost Pisolithus tinctorius vs. uninocuiated P = 5 8 Laccaria laccata vs. uninoculated P 5 9 * Mean of six replicates. f Witbin eacb fungal treatment data followed by different letters are significantly different at P = 5. Data analysed after arcsin transformation. on most species studied (Trappe, 1964), C. geophilum may also cause intracellular infection (Mikola, 1948) and Zak (1973) observed that a given fungus can be either ectomycorrhizal or ectendomycorrhizal on different hosts. The absence of a Hartig net in Hysterangium spp. mycorrhizas has been found previously in eucalypts (Malajczuk et al., 1987). The fungi in our study can he divided into three groups on the basis of host range: (i) those which formed ectomycorrhizas with all plant species tested, (ii) those which formed ectomycorrhizas with only one or two of the hosts tested and (iii) those which colonized roots but failed to initiate ectomycorrhizas. The latter group consists o{ R. luteolus, S. granulatus and S. piperatus which are reportedly 'conifer' specific (Molina & Trappe, 1982). Colonization of the rhizosphere of incompatible host plants hy these fungi has been observed previously (Theodorou &

5 Ectomycorrhizas of Casuarinaceae LSD P ^ 5 for total no. of laterals Weeks from inoculation 2' % Giucose added LSD P = 5 for total no. of laterals Weeks from inoculation 1 2 % Glucose added 7 5 LSD P 5 for total no. of laterals Figure l(a~c). For legend see p Weeks from inoculation 2 % Glucose added

6 284 C. Theodorou and P. Reddell 7 6 % Infection BTotal no. of laterals Weeks from inoculation 2 % Glucose added LSD P = 5 for total no. of laterals Weeks from inoculation 2 % Glucose added 7 6 1% Infection itotal no. of laterals p= o 5 for total no. of laterals Figure \{df) Weeks from inoculation 2' % Glucose added

7 Ectomycorrhizas of Casuarinaceae 285 Bowen, 1971; Malajczuk et al., 1984), Malajczuk et al. (1984) suggested that the failure to initiate ectomycorrhizas is associated with hypersensitive reactions m cells of the colonized roots. The six genera of fungi which formed ectomycorrhizas with both Casuarina spp. and A. littoralis represent diverse taxonomic groups. With the exception of T. terrestris, all are considered to be broad hostrange genera which also associate with Eucalyptus spp. T. terrestris did not form ectomycorrhizas with Eucalyptus spp. in the pure culture study of Malajczuk et al. (1982), however, an undescribed species of Thelephora commonly forms sporocarps beneath natural stands of C. equisetifolia, A. littoralis and Acacia spp. on coastal dunes in northeastern Queensland (P. Reddell, unpublished). Two other broad hostrange fungi, Amanita sp. and P. involutus, formed abundant ectomycorrhizas in association with A. littoralis. However, except for a few ectomycorrhizas produced by Amanita on C. cunninghamiana, these fungi did not infect the two Casuarina spp. Most ectomycorrhiza] fungi show a low degree of host specificity, but under certain situations the fungal symbionts may exhibit a higher degree of specificity for their host species (Chilvers, 1973; Malajczuk et ai, 1982). The reasons for this apparent specificity in our study were not investigated. The results of these pure culture syntheses demonstrate that both Allocasuarina spp. and Casuarina spp. are capable of forming ectomycorrhizas with a range of mycorrhizai fungi. Whether these synthesized hostfungus combinations can form ectomycorrhizas in field soil remains to be determined. For example, in natural stands in northeastern Queensland a more diverse range of sporocarps of ectomycorrhizal fungi occur beneath Allocasuarina than under Casuarina (P. Reddell, unpublished). We have recorded only Pisolithus (2 spp.), Scleroderma and Thelephora beneath C. equisetifolia. In comparison, more than 2 genera have been found in association with Allocasuarina littoralis. The ecological importance of ectomycorrhizal infection of Casuarinaceae by fungi such as the ones in these studies remains to be investigated in the field. However, in unpublished experiments we have obtained growth increases ranging from 69 to 173 '^o when A. littoralis, C. equiseiifolia and C. cunninghamiana were inoculated with P. tinctorius in a glasshouse. Another ecological aspect of importance that arises from these studies is that Eucalyptus spp. and Casuarinaceae have common fungal symbionts and in mixed stands there may be the possibility of transfer of nutrients via the fungus from one host species to another in close proximity (Haystead, Malajczuk & Grove, 1988; Finlay & Read, 1986). Intensity of infection on different hosts The intensity' of infection by the two fungi tested was different on different hosts with the ranking for both fungi being A. littoralis > E. pilularis > C. equisetifolia > C. cunninghamiana (Table 4). Inoculation with L. laccata increased production of lateral roots by the three Casuarinaceae species. P. tinctorius had no effect on numbers of laterals produced by the species. There was no eftect of fungi on production of laterals by E. pilularis. Stimulation of lateral root production in Casuarinaceae by L. laccata may be due to production of growth substances (as described by Slankis, 1973). Differences in intensity of mycorrhiza! infection by a fungus on the four host plants were not related to total number of lateral roots. Differential infection rates may depend on the affinity of the fungus to the host (Malajczuk, Lapeyrie & Garbaye, 199) as well as on soil nutritional factors influencing the interaction between the fungus and the host. The results obtained in this experiment confirm field observations that the intensity of ectomycorrhizal infection is higher on Allocasuarina spp. than on Casuarina spp. (Reddel et al., 1986). This may also be related to the more frequent occurrence of Allocasuarina sp. on sites where Pdeficiency is the major nutritional limitation to plant growth. The comparative dependence of Casuarina and Allocasuarina on ectomycorrhizas in infertile soils requires further investigation. Effect of exogenous supply of glucose on mycorrhizal infection Eight weeks after inoculation, exogenously supplied glucose induced greater ectomycorrhizal infection in all hostfungus combinations with the exception of C. equisetifolia inoculated with L. laccata with 2% glucose (Fig. 1). For al! combinations the optimum glucose concentration for maximum infection was 5'^'o [equi\"alent to 75/^m glucose (g soil)"']. Additions of glucose beyond 5 "o depressed mycorrhizal infection. The exogenous supply of glucose induced earlier mycorrhiza] infection of C. equi Figure 1. Effect of different concentrations of glucose added to the soil on mycorrhizal infection on Allocasuarina littoralis, Casuarina equisetifolia and Casuarina cunninghamiana. (a) A. littoralis inoculated with Pisolithus tinctorius, (b) A. littoralis inoculated with Laccaria laccala, (c) C. equisetifolia inoculated with P. tinctorius, (d) C. equisetifolia inoculated with L. laccata, (c) C. cunninghamiana inoculated with P. tinctorius, (f) C. cunninghamiana inoculated with L. laccata. At 8 wk "o infection bars with different letters are significantly different at P = 5. (Analysis of arcsintransformed data.)

8 286 C. Theodorou and P. Reddell 4 weeks after inoculation LSD P = 5_,g ^^^^^ g^g^ inoculation 6 weeks after inoculation VOO 2 7 weeks after inoculation 8 weeks after inoculation (f) 4 weeks after inoculation 6 P = 5 6 LSD P = 5^6 weeks after inoculation Ds weeks after inoculation % Glucose added

9 Ectomycorrhizas of Casuarinaceae 287 setifolia and C. cunninghamiana by P. tinctorius and A. littoralis by L. laccata. There were also some differences between hostfungus combinations in the intensity of infection (Fig. 1). The effect of glucose in increasing '^/o infection was due to the increased numbers of mycorrhizas formed rather than to a diminishing total number of laterals. Glucose also increased the length of root colonized (Fig. 2) and the intensity of the fungal growth in the rhizosphere, which ranged from slight to moderate in the absence of glucose and heavy to very heavy when glucose was added. The increased intensity of colonization of the roots by the inoculated fungus with added glucose suggests that, under the conditions of the experiment, exudation by the host could not support optimum fungal growth, colonization and infection. This indicates that in the field mycorrhizal infection may depend largely on the growth stimulation that the host may provide to the fungus in the rhizosphere through exudation of growth substances and on the ability of the fungus to compete for such substances by itself or through synergism with other microorganisms (Bowen & Theodorou, 1979; Garbaye & Bowen, 1989). From these results it is evident that an exogenous supply of glucose induces greater, and sometimes earlier, ectomycorrhizal infection in the Casuarinaceae. The optimum supply for mycorrhizal infection was ISO fig glucose (g soil)"^ (12 ml of 5 "o glucose solution in 8 g soil). When the glucose level was increased to 15 mg and 3' mg glucose (g soil)"', mycorrhizal infection declined, although it was often higher than the control. Duddridge (1986) observed that an exogenous supply of glucose affected the interaction between the fungus and the host with the fungus becoming more aggressive and inducing a defence response in the compatible host or killing the incompatible host cells adjacent to the fungus. The decline of intensity of mycorrhizal infection with levels of glucose higher than 5 ",j was probably because of decreased colonization of the root by the fungus and/or a defence response by the host. We did not examine the ultrastructure of the mycorrhizas obtained. REFERENCES BA. A.M.. SorGorFARA, B. & THOEN, D. (1987). The triple symbiosis of Casuarina equisetifolia in Senegal. In : Mycorrhisas in the Next Decade (Ed. by D. M. Sylvia, L. L, Hung & J. H. Graham), p University of Florida, Gainsville, Florida. BARI.OW, B. A. (1983). Casuarinas a taxonomic and biogeographic review. In: Casuarina Ecology. Management and Utilization (Ed. by SJ, Midgley, J. W. Turnhull & R. D. 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(d) C. equisetifolia inoculated with L. laccata, {e), C. cunninghamiana inoculated with P. tinctorius, (/) C. cunninghamiana inoculated with L. laccata.

10 288 C. Theodorou and P. Reddell of Casuarinactae in relationship to host species and soil prijperties. Australian Journal of Botany 34, , RoviRA, A. D. (1959). Root txcretions in relation to the rhizosphere effect. IV. influence of plant species, age oi plant, tight, temperature and calcium nutrition on exudation. Plant and Soil SL.ANKrs. V. (1973). Hormonal relationships in mycorrhiza! development. In: Ectoniycorrhisae: Their Ecology and Physiology (Ed. by G. C. Marks & T. T. Kozlowski). pp 'Academic Press. New ^ork. Soil. SiRVEY SiAFF (1975). Soil Taxonomy : a basic system of soil classihcation for makin(^ and interpreting soii surveys. USDA Handbook 436. l^.s. Government Printing (Office, Washington D.C. THEODOROI'. C. & BOWEN, G. D. (1971). Effects of nonhost plants on growth of mycorrhizal fungi of radiata pine. Australian Forestry 35, TRAPPE, J. M. (1962). Fungus associates of ectotrophic mycorrhizae. The Botanical Re^ieu TRAPPE, J. M. (1964). Mycorrhizal hosts and distribution of Cenococcum graniforme. Lloydia 27, 1(116. TRAPPE, J. M. (1971). Mycorrhizaforming ascomycetes. In: Mycorrhizae (Ed. by E. Hacskaylo), pp. 1937, USDAForest Service, U.S. Government Printing Office, Washington, D.C. ZAK, B. (1973). Classification of ectomycorrhizae. In: Ectomycorrluzae: Their Ecology and Physiology (Ed. by G. C. Marks & T, T. Kozlowski), pp Academic Press, New York.

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