Mycorrhizal diversity in photosynthetic terrestrial orchids

Abstract

Summary• Specific orchid-fungal associations are known for nonphotosynthetic orchids but fungal diversity in photosynthetic orchids is thought to be quite broad. Specific fungal associations will figure prominently in conservation efforts, while diverse associations may require less attention. We combined culture techniques with ITS and mtLSU sequences and phylogenetic analysis to determine the genetic diversity of mycorrhizal fungi associated with an evergreen, a spring-green, and a winter-green orchid and compared this diversity with that published for a nonphotosynthetic orchid.• Mycorrhizal diversity in two of the three photosynthetic orchids was lower than for the nonphotosynthetic orchid. Mycorrhizal diversity in protocorms of the third species was also equal to, or less than, the fungal diversity associated with the nonphotosynthetic species, but adult fungal diversity was greater.• We found that photosynthetic orchids do not necessarily have more diverse mycorrhizal associations than nonphotosynthetic orchids. Similarly, evergreen orchids do not necessarily have greater mycorrhizal diversity than seasonally green orchids. Thus, orchid mycorrhizal diversity may not be determined by adult photosynthetic capacity.

Analysis of fungal diversity in Orchis tridentata Scopoli

“…Moreover, symbionts of a number of orchids are difficult or impossible to cultivate axenically [9,35,36], as confirmed from the results obtained through the in vitro isolation attempts performed in our work. As a consequence, molecular methods, based on PCR, used to directly identify fungi within O. tridentata roots, have been essential to characterize fungal diversity in this orchid.…”

Germination Ecology of the Boreal-Alpine Terrestrial OrchidDactylorhiza lapponica(Orchidaceae)

“…2 isolated from adult Dactylorhiza lapponica plants (Fig. 3) (Taylor et al 2002), although McCormick et al (2004) found high fungal specificity in three green North American species. Muir (1989) found enhanced germination in species of Dactylorhiza, Orchis and Serapias from several fungal isolates, especially on the early stages of development.…”

“…Seeds of Liparis lilifolia, for example, will not germinate in the field or laboratory unless an appropriate fungus is present. The same fungus occurs at all life history stages (Whigham et al 2006) and it is very similar genetically across the range of distribution of the orchid (McCormick et al 2004). Beyond the seeding stage, all terrestrial orchids that were examined are mycorrhizal during some part of the growing season (Rasmussen 1995).…”

Enigmatic Sebacinales

“…Sebacinoid mycobionts were found in wet habitats in roots of Dactylorhiza incarnata. According to McCormick et al (2004), ORMs of the photosynthetic terrestrial Cephalanthera austinae, Goodyera pubescens, Liparis lilifolia, and Tipularia discolor from the eastern and mid-western USA, comprise Sebacina, although details cannot be found in the data presented. Identification and molecular phylogeny of Epulorhiza isolates from tropical orchids comprised both Sebacina and Tulasnella mycobionts (Ma et al 2003).…”