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HORTSCIENCE 38(6):1163–1166. 2003. Berta and Bonfante-Fasolo, 1983; Bradley et al., 1981; Leake and Read, 1989). Other studies have attempted to evaluate the host Host Range of a Select Isolate of range of ericoid fungi, but have inoculated with unidentified ericoid fungal isolates, described, the Eri coid Mycorrhizal Fungus for example as, “dark, slow-growing cultures” (Pearson and Read, 1973b; Reed, 1987). Hymenoscyphus ericae To date there have been no studies that investigate the host range of a select isolate Nicole R. Gorman1 and Mark C. Starrett2 of the ericoid endophyte H. ericae. Therefore, Department of and Soil Science, University of Vermont, Burlington, the objective of this study was to evaluate the VT 05405-0082 host range using select within the Eri- caceae by inoculating with a specific iso late Additional index words. , Calluna, , Gaultheria, Kalmia, , of H. ericae. Oxydendrum, , Rhodo den dron, Vaccinium Materials and Methods Abstract. Studies were conducted to ex am ine the host range of a select isolate of the ericoid mycorrhizal fungus Hymenoscyphus ericae (Read) Korf and Kernan [American Type of 15 ericaceous species was obtained Culture Collection (ATCC) #32985]. Host status was tested for 15 ericaceous species, in- from commercial seed suppliers [Sheffield·s cluding: Calluna vulgaris (L.) Hull, Enkianthus campanulatus (Miq.) Nichols, Gaultheria Seed Co. (Lock, N.Y.) and F.W. Schumacher procumbens L., Kalmia latifolia L., Leucothoe fontanesiana Sleum., Oxydendrum arbo- Co. (Sandwich, Mass.)]. Seed was cleaned and reum (L.) DC., Pieris flo ri bunda (Pursh) Benth. & Hook., Rhodo den dron calendulaceum counted under a dissecting microscope to se- (Michx.) Torr., Rhodo den dron carolinianum Rehd., catawbiense Michx., lect of similar size, color, and fullness. Rhododen dronmax i mum L., Rhododendron mucronulatumTurcz., Vaccinium corymbosum Preliminary trials were conducted to determine L., and Vaccinium macrocarpon Ait. Arbutus unedo L., an eri ca ceous species that forms the approximate num ber of days to germination arbutoid, not ericoid, mycorrhizae, was used as a negative control. All of the species were for each species. Species were grouped (A–C) colonized by the eri coid isolate with the exception of Enkianthus campanulatus and the according to num ber of days to germination negative control. In oc u la tion with this isolate of H. ericae resulted in a significant increase (Table 1). Grouping species enabled all species in shoot growth. How ever, intensity of root colonization was not correlated to amount of to be inoculated and transplanted at the same shoot growth. In fact, an increase in growth was observed in the two species that lacked growth stage. Simultaneous transplant allowed fungal colonization. for a single harvest date for each replication. Seed treatment and aseptic germination. Mycorrhizal symbioses are the rule rather fungi (Perotto et al., 1995). Select ericaceous On 30 Oct. 1998, seed from group A (Table 1) than the exception in the plant kingdom. Eri- species have been inoculated with unidenti- was surface-disinfested with a dilute so di um coid mycorrhizae, the most specialized type of fied ericoid fungi, often using peat originating hypochlorite solution (0.5% to 1.0%) also endomycorrhizae (Harley and Smith, 1983), from native habitats of ericaceous species, as an containing the surfactant polyoxyethylene are formed between a restricted number of inoculum (Allaway and Ashford, 1996; Brad- sorbi tan monolaurate [Tween 20 (0.005%)]. in the order and a small group ley et al., 1981; Leake and Read, 1989, 1991; Bleach concentrations were determined during of ascomycetous fungi (Smith and Read, 1997). Mitchell and Read, 1981; Pearson and Read, preliminary trials to reduce contamination yet The most well known and widely researched 1973b; Powell and Bates, 1981; Reich et al., retain viability of the seed. As a result, dilution isolate is the ascomycete Hymenoscyphus 1982). The first ericoid fungus to be taxonomi- of the solution used in surface-dis in fes ta tion ericae (Read) Korf and Kernan (Peterson and cally identified, H. ericae (Read, 1974), is the varied between species (Table 1). Seed and Farquhar, 1994).Ericoid hosts have been iden- most intensely researched species (Peterson bleach solution were stirred vig or ous ly for 15 tified in the families Ericaceae, Epacridaceae and Farquahar, 1994). However, other studies min, the solution decanted, and seed rinsed with and, more recently, the nonvascular Hepaticeae have used diverse sources of fungal isolates sterile, distilled water. Seeds were transferred to (Duckett and Read, 1995; Straker, 1996). collected from all over the world (Currah et 60×15-mm poly sty rene disposable petri dishes Previous studies of ericoid mycorrhizae al., 1993; Leake and Read, 1991; Pearson and containing 10 mL sterile water agar (6 g·L–1). have produced varied growth responses in host Read, 1975; Straker and Mitchell, 1985). Many There were five seeds per dish and a total of plants (Bonfante-Fasolo et al., 1984; Brad ley of these studies failed to identify a specific six dishes per species. The dishes were sealed et al., 1981; Currah et al., 1993; Leake and fungal strain (Bannister and Norton, 1974; with Parafilm “M” and enclosed in 0.95-L re- Read, 1991; Powell and Bates, 1981; Read, 1995; Reich et al., 1982; Singh, 1974; Star- Table 1. Seed treatment protocol for asep tic germination of select ericaceous species. rett, et al., 2001; Stribley et al., 1975). These inconsistent results may have resulted from the Ericaceous species Abbreviation of species Groupz Sodium hypochlorite treat ment diverse sources of ericoid mycorrhizae utilized Calluna vulgaris CALL A 0.5% fl in each study. Research indicates that consider- Pieris oribunda PIER A 1.0% Vaccinium corymbosum able genetic diversity may exist among ericoid VACC A 0.5% Arbutus unedoy ARBU B 0.5% Gaultheria procumbensx GAUL B 0.5% Received for pub li ca tion 17 July 2002. Ac cept ed for Rhododendron calendulaceum RCAL B 0.8% publication 2 Jan. 2003. This research was funded Rhododendron carolinianum RCAR B 0.5% by a Fed er al Hatch Grant. Use of trade names in Rhododendron catawbiense RCAT B 0.5% this publi ca tion does not imply endorse ment by the Rhododendron maximum RMAX B 0.8% Vermont Agri cul tur al Experiment Station or the U.S. Rhododendron mucronulatum RMUC B 0.5% Dept. of Agriculture–Agricultural Re search Service Vaccinium macrocarpony VACM B 1.0% of products named nor criti cism of similar ones not Enkianthus campanulatus ENKI C 1.0% mentioned. Statis ti cal assistance of Gary Badger and Kalmia latifolia KALM C 0.5% John Aleong is gratefully ac knowl edged. From a Leucothoe fontanesiana LEUC C 0.5% thesis sub mit ted by N.R.G. in partial fulfillment of Oxydendrum arboreum OXYD C 1.0% the requirements of an MS degree. zSpecies are grouped according to number of days to germination. Grouping allowed all species to be 1Former Graduate Assistant. transplanted and inoculated at the same growth stage. A at 28 d; B at 21 d; C at14 d. 2Associate Professor; to whom reprint requests should ySeeds were cold stratified for 30 d at 1 to 5 °C after surface disinfestation procedure. be addressed. E-mail: [email protected] xSeeds were cold stratified for 60 d at 1 to 5 °C after surface disinfestation procedure.

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sealable plastic bags. The bags were placed in media were used as a guard-row and placed variance assumption asso ci at ed with the analy- a controlled-environment chamber maintained around the perimeter of the rack. The racks sis of variance, data corre spond ing to percent at 22 °C day/20 °C night temperature. A 16- were placed in a controlled-environment colonization was arcsine transformed and h pho to pe ri od was provided by cool-white chamber main tained at 25 °C day/22 °C night number was square root transformed prior to fluorescent lamps and incandescent bulbs. temperature. A 16-h photoperiod was provided analysis. Although statistical significance was Lamps and bulbs provided an average pho- by cool-white florescent tubes suspended 2 cm based on transformed data, means presented tosynthetic pho ton flux [PPF (400–700 nm)] above the tops of the vials. Lamps provided an in tables and figures represent nontransformed of 251 µmol·m–2·s–1 as measured at the top of averagePPFof 58 µmol·m–2·s–1as measured at data. All F tests corresponding to treatment the dishes. These and all other light measure- the top of the vials. These light and temperature comparisons utilized the Replicate × Treat- ments were taken with a LI-COR Quantum conditions were used for the remainder of the ment mean square as the error term. Pairwise Sensor and recorded with a LI-COR 1000 study. This procedure was repeated for each comparisons are based on Fisher·s LSD proce- Data Logger (LI-COR, Lincoln, Nebr.). Petri subsequent replication. dure. Statistical significance was determined dishes were scanned weekly for contamination. Transplant. After incubation, seedlings using P < 0.05. Con tam i nat ed dishes were removed from the with fully ex tended cotyledons were chosen bags and discarded. for trans plant ing. Seedlings were aseptically Results Three species, Arbutus unedo, Gaulth e ria trans ferred to the vials. An additional 1.0 mL procumbens, and Vaccinium macrocarpon, of sterile, liquid WPM was added to each vial All of the ericaceous species tested, in- re quired cold stratification fol lowing sur- at the time of transplant. Vials were recapped clud ing G. procumbens, K. latifolia, L. fonta- face-disinfestation procedure. Seeds of these with Ma gen ta-caps and sealed with Parafilm nesiana, O. arboreum, P. fl oribunda, R. calen- species were surface-disinfested prior to the “M.” The racks were placed back into the dulaceum, R.carolinianum, R. catawbiense,R. other species examined to allow for their controlled-environment chamber following maximum, R. mucronulatum, V. corymbosum, required stratification period. During strat- transplant. Transplant of seedlings of each and V. macrocarpon, with the exception of E. ification, seeds were placed in the dark in a replicate was separated by 1 week. campanulatus and the negative control, A. un- refrigerator maintained at 1 to 4 °C for 30–60 Harvest. On 10 Feb. 1999, 60 d from edo,were colonized by the isolate (Table 2). The d (Table 1). trans plant of seedlings, the first replication was lack of colonization in A. unedo was expected Preparation of inoculum.An actively grow- harvested. Plants were divided into shoots and since this species forms arbutoid, not ericoid, ing fungal isolate of H. ericae was obtained roots. Root samples were prepared to deter mine mycorrhizae. Sur pris ing ly, E. campanulatus, a from the American Type Culture Collection extent of fungal colonization. Each root sample species thought to form typical ericoid mycor- [ATCC# 32985 (Rockville, Md.)]. Using was placed in a beaker and gently washed in rhizae, also was not colonized. Because the aseptic techniques, the isolate was subcultured distilled water. Any remaining grow ing media host status of the latter species has not been and grown on Bacto malt agar (45 g·L–1) for was teased from the roots in distilled water un- tested with any ericoid mycorrhizal fungus, §8 weeks. Fungal cultures were placed in a der a dissecting microscope. The samples were this lack of colonization is of note. controlled-environment chamber maintained then cleared and stained follow ing a protocol Significant differences were detect ed in at constant temperature of 23 °C. During in- adapted from Brundrett et al. (1984) and exam- mean percent colonization among species fi cubation, a 16-h photoperiod was provided by ined using bright eld mi cros co py. To quantify (F14,39 = 13.42, P< 0.0001). The greatest degree cool-white fluorescent tubes suspend ed 24 cm root colonization, indi vid u al roots from each of infection was observed in R. carolinianum above the tops of the petri dishes. Tubes emitted seedling were random ly selected and exam- (65%), and the least was found in E. cam- an average PPFof 17 µmol·m–2·s–1 as measured ined for the presence of infected cells. Five panulatus (0%). Significantly great er per cent at the top of the petri dishes. Care was taken random views per root system were sampled colonization was observed in the spe cies R. to select dark, slow-growing, uniform cultures at ×400. Thirty con tig u ous cortical cells were carolinianum, P. fl oribunda, V. macrocarpon, as an in oc u lum. counted per view to determine the percentage K. latifolia, and L. fontanesiana as compared Preparation of growing media. On 20 Nov. of cells colonized. Each view under the scope to the species R. calendulaceum, O. arboreum, 1998, 3 weeks prior to transplant of seedlings was considered an observation. An average of from the first rep li ca tion, sixty 75-mL vials five observations was cal cu lat ed as the mean were filled with 25 mL vermiculite moistened colonization of a single seedling. Table 2. Mean percent root cell colo ni za tion of with 5 mL distilled water and 6 mL Woody Experimental design and statistical anal- select ericaceous species by Hymenoscyphus Plant Medium [WPM (Lloyd and McCown, y sis.The experimental design consisted of four ericae (ATCC #32985) after incubation for 1980)] supplemented with sucrose (5 g·L–1). replicates, or blocks, consisting of 15 species 60 d in vitro. This medium was adjusted to a pH of 5.2 with that were staggered by §1 week for manage- Species Meanz SDy 1 N HCl prior to addition to vials. Vermiculite ability in set-up and eval u a tion. Each replicate Rhododendron carolinianumx 64.6 a 20.0 was chosen for use as the growing medium as contained 60 vials, repre sent ing four seedlings Pieris fl oribunda 64.3 a 22.5 opposed to using native soil excised from an (one per vial) of each of the 15 species, two Vaccinium macrocarpon 60.9 ab 8.0 existing ericaceous plant community due to of which were inoculated with H. ericae, and Kalmia latifoliax 58.9 ab 11.2 the problems associated with sterilizing soils two that re mained noninoculated. The 60 seed- Leucothoe fontanesiana 58.1 ab 12.5 contain ing peat (Stribley et al., 1975). Vials lings were randomized spatially within each Rhododendron maximum 45.7 a–c 27.2 were covered with Magenta-caps (Magenta repli cate. This design constitutes a ran domized Rhododendron catawbiense 41.9 b–d 14.6 Vaccinium corymbosum 40.6 b–d 15.9 Corp., Chicago) and autoclaved for 15 min at complete block (RCBD), in which 30 treat- Gaultheria procumbens 39.8 b–d 6.9 121 °C. Vials were allowed to cool overnight in ments have a factorial structure (15 species Rhododendron calendulaceum 30.6 cd 19.6 a laminar flow hood. On 21 Nov. 1998, hyphae × 2 inoculation states). For each seedling, an Oxydendrum arboreum 29.8 cd 3.2 of ericoid mycorrhizal fungi were transferred estimate of intensity of colonization was based Calluna vulgarisx 23.4 de 5.5 aseptically to vials containing the vermic u lite on the average of five randomly de ter mined Rhododendron mucronulatum 12.6 e 12.5 media. Wefts of §3 mm3 growing actively on ×400 views of randomly selected hair roots, Arbutus unedo 0 f 0 the surface of 1-month-old malt agar cultures each resulting in an estimate of percent of root Enkianthus campanulatus 0 f 0 of H. ericae were transferred to 30 vials. A cells colonized. Number of and stem zMeans are based on four replicates of two seedlings second set of 30 vials remained noninoculated length was also recorded for each seedling. each. Percent colonization based on five random views per seedling. Means not sharing a common (controls). Vials were recapped, sealed with Statistical analyses were performed using fi Parafilm “M,” and placed in Magenta 7-way SAS (SAS Institute, 1989a, 1989b). Species letter are signi cantly dif fer ent (Fisher·s LSD, P < 0.05). tray racks (Magenta Corp.). The racks allowed comparisons on colonization intensity (i.e., yStandard deviation associated with rep li cates. for 0.5-cm spacing between vials. To create mean percent root cell colo ni za tion) are based xMean based on three replicates due to either inad- similar light and temperature conditions for on analysis of variance limited to the inoculated equate germination or death at trans plant. Means are all cultures, vials containing only the growing seedlings. In order to satisfy the homogeneity of calculated from values of living plants only.

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24-7399, p1163-1166 1164 10/16/03, 1:02:13 PM the exception of K. latifolia and L. fontanesi- ana, were observed to have a greater percent increase in leaf number than the more heav- ily colonized R. carolinianum. Ad di tion al ly, inoculated seedlings of G. procumbens, L. fontanesiana, R. catawbiense, R. maximum, and R. mucronulatum all exhibited a greater percent increase in stem length as compared to R. carolinianum. In fact, E. campanulatus, which was not colonized at all, exhibited an increase in both shoot length and leaf number and A. unedo, also not colonized by H. ericae, exhibited a significant increase in stem length. The possible factors contributing to increased growth with inoculation of H. ericae with low or without any root colonization are con sidered in the following discussion.

Discussion

The isolation, culture, and development of typical mycorrhizal structures are only the first steps in determination of the nature of the mycorrhizal relationship (Leake and Read, 1991). One of the complexities of my c or rhizae is demonstrated in this study by the inability to differentiate between the effect of inoculation and the effect of mycorrhiza for ma tion. For practical purposes, an additional difficulty lies in the determination of which host responses are most appropriate to mea sure for accurate prediction of increased host productivity. Percent colonization may not be a good indicator of plant productivity, indicated by the lack of correlation in this study between col o ni za tion intensity and the two growth re- sponses (leaf number and stem length). Other research ers have also observed a lack of cor- relation between intensity of colonization and growth response in ericaceous plants inoculated Fig. 1. In vitro grown seedlings of eri caceous speciesinoculated with Hymenoscyphus ericae (ATCC with ericoid fungi (Starrett et al., 1996). In fact, #32985). (A) mean stem length (+SE). (B) mean leaf number (+SE). Sig nificant dif fer enc es between inoculated and noninoculated, independent of species (P < 0.05). there may be differences in the host–fungus relationship between species as a result of the varied conditions under which the asso ci a tions

C. vulgaris, and R. mucronulatum. Rhododen- species (F14,80 = 0.68, P= 0.784). The mean leaf have evolved. Read (1996) hypothesized that dron mucronulatum exhibited the least degree number across all inoculated spe cies in creased the function of ericoid mycorrhiza may actually of infection of all the colonized species and §1.3× that of the nonin oc u lat ed seedlings. All differ among ericaceous populations. Addition- differed significantly from all species except of the in oc u lat ed species exhibited an increase ally, Goulart et al. (1993) surveyed native and C. vulgaris. in leaf number as com pared to the noninocu- commercial populations of Vaccinium in the Analyses relating to stem length indi cat ed lated seedlings, with the exception of K. lati- northeastern and mid west ern and a positive response to inoculation (Fig . 1A). folia, L. fontanesiana, and R. carolinianum. found a high degree of variation in infection. Statistical analysis revealed signi ficant dif fer - For the species R. carolinianum, no change Again, this indicates that there could be other enc es in mean stem length between inoculated was ob served in leaf number of inoculated as factors contributing to the variation in intensity

and noninoculated seedlings (F1,80 = 52.95, P = compared to noninoculated seedlings. Kalmia of colonization. 0.0001) although there was no evidence that this latifolia and L. fontanesiana exhibited a de- The increase in growth in the species E. fi difference was species spe ci c (F14,80 = 1.48, P crease in leaf number as compared to nonin- campanulatus and A. unedo, both without = 0.140). In general, inoculated seed lings ex- oculated seedlings. Interestingly, A. unedo, col o ni za tion, may seem unusual. However, hibited a relatively large increase in mean stem one of the species that was not colonized by similar results have been shown in other length across all inoc u lat ed spe cies. In fact, H. ericae, exhibited a greater percent increase studies. Linderman and Call (1977) also ob- stem length across all species was increased in leaf number than several colonized species served an increase in root formation without more than 2-fold over the noninoculated seed- including: K. latifolia, L. fontanesiana, O. ar- my c or rhizal formation in ericaceous species. lings. The greatest increase was observed in boreum, R. carolinianum, R. maximum, and R. Select ectomycorrhizae have been shown to L. fontanesiana, being more than 5-fold that mucronulatum. release growth factors, such as auxin, cyto- of the noninoculated seed lings. Statistical analysis revealed that there was kinins, gibber el lins, and B-vitamins in vitro Analyses relating to leaf number also indi - no correlation of intensity of colo ni za tion to an (Slankis, 1973), but release of such compounds cat ed a positive response to in oc u la tion (Fig . increase in shoot length or leaf number. Rho- has not been demonstrated by H. ericae. It 1B). Statistical analysis revealed signi ficant do den droncarolinianumwas the most heavily is certainly possible that the physical and/or differences in mean leaf number between infected; however, inoculated seedlings did not chemical composition of the growing media

inoculated and noninoculated seed lings (F1,80 respond with an increase in stem length or leaf was changed by the inoculum. However, none = 9.08, P = 0.004) although there was no number as compared to the other in oc u lat ed of these factors have been investigated in the evidence that this difference was speci fic to species. All of the inoculated species, with present study.

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Variability in colonization of seedlings cor rhizal infection and resistance to heavy cor rhizae stimulate yield of blueberry. within species may have resulted from the metal toxicity in Calluna vulgaris. Nature 292: HortScience 16:655–656. genetic variability associated with seed prop- 335–337. Read, D.J. 1974. Pezizella ericaesp. nov., the per fect a ga tion and the short duration of the project. Brundrett, M.C., Y. Piché, and R.L. Peterson. 1984. state of a typical mycorrhizal en do phyte of erica- Seedlings may not have had adequate time A new method for observing the morphology of ceae. Trans. Br. Mycol. Soc. 63:381–382. vesicular–arbuscular myc or rhizae. Can J. Bot. Read, D.J. 1983. The biology of my c or rhi za in the for uniform mycorrhizal development. A 62:2128–2134. Ericales. Can. J. Bot. 61:985–1004. pos si ble method for reduction of variability Currah, R.S., A. Tsuneda, and S. Murakami. 1993. Read, D.J. 1995. The biology of my c or rhi za in the due to genetic variation is the use of clonal Morphology and ecology of Phialocephala for- Ericaceae. XVIII. Chitin deg rada tion by Hymen- plant material, such as rooted microcuttings, tinii in roots of Rhodo den dron brachycarpum. oscyphus ericaeand transfer of chitin-nitrogen to and needs further investigation. Can. J. Bot. 71:1639–1644. the host plant. New Phytol. 131:369–375. The isolate of H. ericae used as the in- Duckett, J.G. and D.J. Read. 1995. Ericoid myc or - Read, D.J. 1996. The structure and func tion of ocu lum for this study was originally isolated rhi zas and rhizoid-ascomycete as so ci a tions in the ericoid mycorrhizal root. Ann. Bot. 77: from C. vulgaris. Therefore, one would expect liverworts share the same mycobiont: Isolation 365–374. this species to be intensely colonized. To the of the partners and resynthesis of the asso ci a tions Reed, M.L. 1987. Ericoid mycorrhiza of Epacrida- in vitro. New Phytol. 129:439–447. ceae in Australia, p. 335. In: D.M. Sylvia, L.L. con trary, C. vulgaris exhibited relatively low Goulart, B.L., M.L. Schroeder, R.L. Darnell, J.R. Hung, and J.H. Graham (eds.). Proc. 7th North root colonization (Table 2). Starrett et al. Clark, and W.F. Wilcox. 1993. Blueberry my c or - Amer. Conf. on My c or rhizae, 3–8 May 1987. (1996) also observed this lack of host speci- rhizae: Current knowledge and future di rec tions. Univ. of Florida, Gainesville. ficity among ericoid isolates. Despite this low In: Proc. 5th Intl. Symp. Vaccinium Cul t. Acta Reich, L.A., R.F. Korcak, and A.H. Thomp son. col o ni za tion, C. vulgaris had the greatest per- Hort. 346:230–239. 1982. The effect of selected soil factors on cent increase in leaf number of all the species Harley, J.L. and S.E. Smith. 1983. Myc or rhizal growth and nutrient content of high bush blue- tested. An §2-fold increase in stem length was symbiosis. Academic Press, New York. ber ry (Vaccinium corymbosum L.) J. Amer. Soc. also observed; however, the percent increase Leake, J.R. and D.J. Read. 1989. The effects of Hort. Sci. 107:943–946. was less than all inoculated species with the phenolic compounds on nitrogen mobilisation SAS Institute. 1989a. SAS/STAT us er·s guide, ver. fl by ericoid mycorrhizal systems. Agr. Ecol. En- 6, 4th ed., vol. 1. SAS Inst., Cary, N.C. exception of V.corymbosum, P. oribunda, and viron. 29:225–236. SAS Institute. 1989b. SAS/STAT user ·s guide, ver. E. campanulatus. Leake, J.R. and D.J. Read. 1991. Exper i ments with 6, 4th ed., vol. 2. SAS Inst., Cary, N.C. Read (1983) stated that all plants in the ericoid mycorrhiza, p. 435–460. In: J.R. Nor- Singh, K.G. 1974. Mycorrhiza in the Ericaceae with Ericaceae are mycorrhizal. Therefore, the lack ris, D.J. Read, and A.R. Varma (eds.). Methods special reference to Calluna vulgaris. Sven. Bot. of colonization observed in E. campanulatusis in microbiology, vol. 23. Academic Press, San Tidskr. 68:1–16. of particular interest. Further study is neces sary Diego, Calif. Slankis, V. 1973. Hormonal relationships in Myc or - to determine whether E. campanulatus forms Linderman, R.G. and C.A. Call. 1977. Enhanced rhizae, p. 231–298. In: G.C. Marks and T.T. Ko- another type of association, such as arbutoid rooting of woody plant cuttings by mycorrhizal zlowski (eds.). Ectomycorrhizae, their ecol o gy mycorrhizae that develop on other species in the fungi. J. Amer. Hort. Sci. 105(5):629–632. and physiology. Academic Press, New York. Lloyd, O. and B. McCown. 1980. Com mer cial ly- Smith, S.E. and D.J. Read. 1997. My c or rhizal Ericales, such as A. unedo and Arctostaphylos feasible micropropagation of mountain laurel, sym bi o sis. 2nd ed. Academic Press, San Di- uva-ursi (L.) Spreng. Kalmia latifolia, by use of shoot-tip culture. Proc. ego, Calif. Intl. Plant Prop. 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