Ectomycorrhizal Inocybe species associate with the mycoheterotrophic orchid Epipogium aphyllum but not its asexual propagules

Abstract

Microscopic investigations revealed that thick rhizomes were densely colonized by fungi bearing clamp-connections and dolipores, i.e. basidiomycetes. Molecular analysis identified Inocybe species as exclusive symbionts of 75 % of the plants investigated and, more rarely, other basidiomycetes (Hebeloma, Xerocomus, Lactarius, Thelephora species). Additionally, ascomycetes, probably endophytes or parasites, were sometimes present. Although E. aphyllum associates with diverse species from Inocybe subgenera Mallocybe and Inocybe sensu stricto, no evidence for cryptic speciation in E. aphyllum was found. Since basidiomycetes colonizing the orchid are ectomycorrhizal, surrounding trees are probably the ultimate carbon source. Accordingly, in one population, ectomycorrhizae sampled around an individual orchid revealed the same fungus on 11.2 % of tree roots investigated. Conversely, long, thin stolons bearing bulbils indicated active asexual multiplication, but these propagules were not colonized by fungi. These findings are discussed in the framework of ecology and evolution of mycoheterotrophy.

Why do mixotrophic plants stay green? A comparison between green and achlorophyllous orchid individuals in situ

“…We note that MX Cephalanthera species strongly differ in this respect from MH orchids, which display denser and continuous colonization (Rasmussen andWhigham 2002, Tatarenko 2002), including in summer, as exemplified by the sympatric Neottia nidus-avis (Selosse et al 2002; M.-A. Selosse, personal observation) and Epipogium aphyllum (Roy et al 2009b); alternatively, MH orchids seasonally lacking fungal colonization accumulate reserves in tuberized roots or rhizomes (such as the tropical MH Wullschlaegelia aphylla during the dry season; Martos et al 2009). The latter patterns allow a constant C supply, which albino mycorrhizae cannot ensure.…”

“…For each leaf, 10 counts of stomata number were performed at 4003 magnification, randomly on the leaf. To measure leaf and cuticle thickness, 1 cm 2 from each of these leaves was collected at the edge, fixed in 2.5% (volume by volume [v/v]) glutaraldehyde in a 10 mmol/L Na-phosphate buffer (pH 7.2), and embedded as in Roy et al (2009b). Then, transverse sections (10 lm) were cut with a microtome, differentially stained with a mixture of safranin and Fast Green FCF dye, rinsed with distilled water, and observed under the light microscope at a 4003 magnification.…”

“…Rather, we speculate the need for a joint and progressive evolution of, at least: (1) more continuous mycorrhizal colonization (or large C reserves) for permanent C supply, (2) smaller leaves, with fewer or no stomata, (3) reduction of photosynthesis efficiency and pigment content, (4) optimal sprouting and dormancy, selected for fruiting more than for photosynthesizing, and (5) some homochromy and new defenses against parasites and herbivores. Evolution of some additional traits may be required, such as ecological preference for old growth, dark and moist forests (Correll 1950, Leake 1994, or belowground vegetative multiplication structures (Klimesnova 2007, Roy et al 2009b). Since multiple loci are likely involved, evolution of MH plants from MX ancestors (or full fitness remediation in albinos) is unlikely to occur in a single mutational step, and probably involves a progressive, joint evolution among above-mentioned traits.…”

“…As already mentioned, albino shoots have a shorter mean life span than green ones, perhaps because shoots with longer life span are progressively eliminated over the season. Congruently, MH species appear more sporadically (with very variable timing in the year, e.g., for Epipogium aphyllum; Roy et al 2009b) and remain for a shorter time above ground, as compared with photosynthetic species (Leake 2004).…”

A common new species ofInocybein the Pacific Northwest with a diagnostic PDAB reaction

“…Inocybe cf. chondroderma occurs in both Colorado and Japan, where in Japan it associates with the mycoheterotrophic orchid Epipogium aphyllum Sw. (Roy et al 2009). Sister to I. chondroderma and I. cf.…”