Endomycorrhizal Fungus in Chlorophyll-Free and Green Forms of the Terrestrial Orchid Epipactis Helleborine
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Karstenia 28: 3-18. 1988 Endomycorrhizal fungus in chlorophyll-free and green forms of the terrestrial orchid Epipactis helleborine AULIKKI SALMIA SAL:MIA, A. 1988: Endomycorrhizal fungus in chlorophyll-free and green forms of the terrestrial orchid Epipactis helleborine.- Karstenia 28: 3-18. A brown, slowly growing unidentified fungus was isolated from nine (chlorophyll-free, yellowish-green and green) individuals of Epipactis helleborine (L.) Cranz collected from Finland. The brown fungus appeared regularly from sterilized root segments, and four isolates were obtained from hypha! coils in cortical cells of both green and white indi viduals. The results indicate that the same endophyte inhabited white and green plants of E. helleborine, and that the brown fungus can be considered to be the endophyte of this species, though this has not yet been confirmed with symbiotic tests. The effect of dif ferent surface-sterilizing agents on the appearance of the brown fungus from root pieces was investigated. The most suitable sterilization chemical proved to be 0.1% mercuric chloride in 50% ethanol. The morphology and some characteristics of the fungus are de scribed. The growth pattern and microscopic chracateristics of the brown endophyte differ from those of the well-known orchid fungi. No teleomorph could be obtained in culture. Aulikki Salmia, Department of Botany, University of Helsinki, Unioninkatu 44, SF- 00170 Helsinki, Finland Introduction (Burgeff 1936, Curtis 1939, Downie 1959, Smith Under natural conditions, the absorbing organs, roots 1966, Harvais & Harley 1967, Warcup & Talbot or rhizomes of most members of the Orchidaceae are 1967, Hadley 1970, Warcup 1981a, Terashita 1982, infected by intracellular fungi, which form coils of Alexander & Hadley 1983, Filipello Marchisio et al. hyphae within the cortical cells. Successful isolation 1985, Currah 1987). of the endophyte depends on the methods used (e.g. Almost all the fungi isolated, especially those from surface sterilizing, media), degree of infection and green orchids, have been assigned to the form genus viability of the hypha! coils. Probably due to its Rhizoctonia. The generic complex of Rhizoctonia is, efficiency, mercuric chloride (usually in water) has however, rather variable and ill-defined (Parmeter & been widely used as sterilizing agent in many orchids Whitney 1970, Tu & Kimbrough 1975). Perfect (Burges 1939, Curtis 1939, Downie 1959, Smith stages of Rhizoctonia are known to belong to the 1966, Harvais & Hadley 1967). Other chemicals that Basidiomycetes and Ascomycetes (see e.g. Whitney have been used for orchid root pieces are 9% & Parmeter 1964, Warcup 1975). Species in the hydrogen peroxide (Alexander & Hadley 1983), Rhizoctonia complex produce a wide variety of teleo 0.4% silver nitrate (Filipello Marchisio et al. 1985), morphs belonging to several families of the Basio sodium or calcium hypochlorite (Harvais 1974, Bar diomycetes, such as the Tulasnellaceae (Tulasnella roso et al. 1986a, b) and ethanol (Nieuwdorp 1972). spp.), Ceratobasidiaceae (Ceratobasidium spp., Tha If mature plants are infected by viable coils, the endo natephorus spp., Ypsilonidium spp.) and Tremella phytic fungi can be fairly easily isolated from roots, ceae (Sebacina vermifera) (see Warcup & Talbot especially in early or mid-summer. A considerable 1966, 1967, Harley 1969, Warcup & Talbot 1971, number of orchid fungi have been obtained in culture, Warcup 1975, Tu & Kimbrough 1978, Arditti 1979, usually by using potato dextrose agar or some other Warcup & Talbot 1980, Warcup 1981b, Hadley medium such as malt, cornmeal, or Dox-yeast agar 1982, Harley & Smith 1983). 4 SALMIA: ORCI·IID EPIPACTIS HELLEBORINE KARSTENIA 28 (1988) "Corticiwn catonii" (Burgeff 1936) and Favo 1943, Warcup & Talbot 1962, 1965, 1966, 1967) laschia dybowskyana (Jonsson & Nylund 1979), and can grow freely in soil, or they may be parasitic which both belong to the Aphyllophorales, have been on a variety of hosts, e.g. Thanatephorus cucwneris shown to be mycorrhizal with orchids. Clamp-form (Rhizoctonia solani) and Armillaria me/lea (Domsch ing and other Basidiomycetous genera which do not et al. 1980). Mycorrhizal infection of orchids differs belong to the Rhizoctonia complex have been identi from other kinds (VA, ectotrophic) in one fundamen fied, for instance, in achlorophyllous orchids: Maras tal respect (Harley & Smith 1983). The net movement mius coniatus in Didymoplexis minor (Burgeff of carbon compounds is from the substrate through 1959), Armillaria me/lea in Galeola septentrionalis the fungus into the host. In other forms of (Hamada 1939, see also Terashita 1985) and in mycorrhiza, carbon compounds originate in photo Castrodia cunninghamii (Campbell 1962), Fornes synthesis by the host and their net movement is into spp. in Galeola hydra (Burgeff 1959) and in Gastro the fungus (Harley & Smith 1983). dia sesamoides (Campbell 1964), and Hymenochaete In Lappeenranta, SE Finland, a population of Epi crocicreas in Galea/a altissima (Hamada & Nakamura pactis helleborine growing on a hill with Scots pine 1963). Three strains of Ascomycetes with rhiwcto as the dominant tree was found to contain normal niaiceous anamorphs have been isolated from Ptero green, yellowish-green and abundant white chloro stylis species in Australia, but all attempts to germi phyll-free individuals (Salmia 1986). All the plants nate Pterostylis seeds with them have been unsuc investigated were regularly and uniformly infected by cessful (Warcup 1975). The presence of some Asco a brown endophytic fungus, which was readily seen mycetes as endophytes has been established in tropi in whole mounts of root sections (Salrnia 1989). As cal orchid epiphytes (Petrini & Dreyfuss 1981, Drey both the green and chlorophyll-free plants of E. helle were shown to be infected, it was interesting fuss & Petrini 1984). A vesicular-arbuscular mycor borine to find out whether the fungi were identical, too. This rhiza has even been reported in the orchid Corybas paper deals with the isolation and properties of the macranthus (Hall1976). Many reports of the endophytic fungi of European endophytic fungi of the white and green plants. orchids are fairly old and sporadic and the attempts to obtain perfect stages of Rhizoctonia -like or other orchid fungi in culture have often been unsuccessful Plant material (see e.g. Filipello Marchisio et al. 1985). For in Mature plants of the broad-leaved helleborine (Epi stance, the perfect stages of the endophytes of the pactis helleborine (L.) Cranz) were collected from European saprophytic orchids are still unknown (see Lappeenranta, Finland; on 24 July 1981 (two plants, however Campbell 1970). Without the perfect stage, chlorophyll-free and normal green) and on 31 July the identification is extremely difficult and unsure and 1982 (8 plants: chlorophyll-free la-c; yellowish can be made only by comparing the data with those in green 2a, b; normal green 3a--c). For the site and the literature. In some European green orchids, how other details, see Salmia ( 1986, 1989). In addition, ever, endomycorrhizal fungi have been identified. two normal green plants were collected on 20 October Rhizoctonia goodyerae-repentis (perfect stage Cerato 1982 from Stromnas, Kemio, Finland; from sunny basidiwn cornigerum, cf. Warcup & Talbot 1966) calcareous bedrock with scattered Scots pines. The has been isolated from Goodyera repens (Downie field layer of the latter site contains Asplenium ruta 1940, Hadley 1970, Alexander & Hadley 1983), muraria, A. septentrionalis, Woodsia ilvensis, and Rhizoctonia so/ani ("Corticiwn so/ani", perfect stage Geranium sanguinewn (B. Linden, pers. comm.). Thanatephorus cucumeris, cf. Warcup & Talbot The localities, Lappeenranta and Kemio, are ca. 330 1967) from Dactylorchis purpurella (cf. Downie km apart. The plants were carefully removed from the 1957, 1959, Harvais & Hadley 1967) and from ground to ensure that the root system was kept intact. Coeloglossum viride (Harvais & Hadley 1967), E. helleborine has abundant long straight roots, the Thanatephorus orchidicola from Orchis mascula colour ranging from light to dark brown (Salmia (Warcup & Talbot 1966) and from Coeloglossum 1986, Fig. 6). The plants were grown in pots in a viride (Warcup & Talbot 1967), Thanatephorus pen greenhouse until the isolation of the fungi was natus from Calypso bulbosa (Currah 1987), and performed. Rhizoctonia repens (perfect stage Tulasnella calo spora) from Dactylorchis purpurella, Dactylorchiza maculata and Plantanthera bifolia (Warcup & Talbot 1967, Harvais & Hadley 1967, Hadley 1970). Isolation of endophyte(s) Some orchid endophytes, e.g. Ceratobasidium Preliminary studies, plants collected in cornigerum, are terrestrial saprophytes (Downie 1981. Two attempts were made to isolate the endo- KARS1ENIA 28 (1988) SALMIA: ORCIDD EPIPACTIS HELLEBORINE 5 phyte(s) of Epipactis helleborine. For mild sterilizing, PDA and cornrneal agar (CMA, Difco). The growth the root pieces were submerged in 70% ethanol (1-5 rates of these isolates were determined by measuring min) and washed with sterile water. Another trial the radial increase in two directions, first weekly dur included sterilizing in 70% ethanol for 3 min, and ing a 5-week period, then after 2 months. The diam several other surface-sterilizing methods: 0.1% eters of hyphae, monilioid cells and chlamydospores mercuric chloride in water 2 min, 1% AgN03 1 min, were measured in glycerol-water. subsequent washing with 4% NaCl (1 min), then