Symbiotic germination and development of myco‐heterotrophic plants in nature: ontogeny of Corallorhiza trifida and characterization of its mycorrhizal fungi

Abstract

The processes of symbiotic germination and seedling development were analysed in the myco-heterotrophic orchid Corallorhiza trifida, seeds of which were buried in ' packets ' either adjacent to or at varying distances from adult plants in defined communities of ectomycorrhizal tree species. Germination occurred within eight months of burial under Betula-Alnus and within seven months under Salix repens. It was always associated with penetration of the suspensor by a clamp-forming mycorrhizal fungus. Four distinct developmental stages were defined and the rates of transition through these stages were plotted. There was no evidence of a relationship between extent of germination or rate of development and the presence of naturally distributed plants of C. trifida at the spatial scale of 1 m. The best germination and the most rapid rate of development of C. trifida seedlings occurred in a Salix repens community located at a considerable distance from any extant C. trifida population. Determination of internal transcribed spacer (ITS) RFLPs and of gene sequences of the fungi involved in symbiotic germination and growth of C. trifida, revealed them to belong exclusively to the Thelephora-Tomentella complex of the Thelephoraceae. These fungi are known also to be ectomycorrhizal associates of trees. It is hypothesized that the rate of growth of the C. trifida seedlings is determined by the ability of the fungal symbionts to transfer carbon from their ectomycorrhizal co-associates.

Symbiotic germination and development of myco‐heterotrophic plants in nature: transfer of carbon from ectomycorrhizal Salix repens and Betula pendula to the orchid Corallorhiza trifida through shared hyphal connections

“…Samples of the seed packets were removed after 14 months and a number of well developed seedlings selected, each with a branched coralloid rhizome 15-25 mm long and with differentiated shoot buds (defined as developmental stage 4 : McKendrick et al, 2000).…”

“…The C maintenance costs of the recruits, because of their very small biomass, is unlikely to be important in this case. The exceedingly small size of the dust-seeds of Corallorhiza precludes their providing a significant contribution to the C economy of the plants beyond their earliest stages of development, stages 1-2 (McKendrick et al, 2000).…”

Symbiotic germination and development of the myco‐heterotrophic orchid Neottia nidus‐avis in nature and its requirement for locally distributed Sebacina spp.

“…In an earlier paper we described the use of these techniques to evaluate the factors influencing germination of the achlorophyllous myco-heterotroph Corallorhiza trifida (McKendrick et al , 2000a). Here, we present the results of an analysis of the symbiotic germination and development of another orchidaceous MHP, Neottia nidus-avis (L) Rich.…”

Indução in vitro da germinação de sementes de Oncidium flexuosum (Orchidaceae) por fungos micorrízicos rizoctonióides

“…As orquídeas utilizam-se da digestão de massas de hifas formadas intracelularmente (pelotons), principalmente nas células do córtex da raiz, como fonte de energia durante o está-dio heterotrófico do seu ciclo de vida (Harvais & Hadley, 1967;Smith & Read, 1997;Peterson et al, 1998). Esse fenômeno, conhecido por micoheterotrofismo, não é exclusivo da família Orchidaceae, sendo também relatado em outras famílias de monocotiledôneas, a saber: Burmanniaceae, Corsiaceae, Lacandoniaceae, Petrosaviaceae e Triuridaceae e em famílias de dicotiledôneas, como: Ericaceae (Monotropoideae), Polygalaceae e Gentianaceae (Leake, 1994;McKendrick et al, 2000;Read et al, 2000;Taylor et al, 2002).…”