Seed dormancy patterns in Epipactis palustris (Orchidaceae): Requirements for germination and establishment of mycorrhiza

Abstract

Some terrestrial orchid species, including Epipactis palustris (L.) Crantz, are considered extremely difficult to germinate and cultivate in vitro. Observations of orchids germinating in nature are very few, and the timing and requirements for seedling establishment are unknown for most species. Seeds of E. palustris were incubated in vitro with an appropriate fungus, but germination was poor unless several other conditions were also met: scarification of the testa in Ca(OCL)2, an initial incubation for several weeks at 27°C, and a subsequent cold stratification for 8–12 weeks at 4–8°C, With these pretreatments, germnation responses exceeded 50% after incubation for 4 weeks at 20°C. Healthy protocorms with normal organ development were only produced by symbiotic culture following this lengthy seed preparation. The findings suggest that under natural conditions the seeds need some after‐ripening, and the testa needs to be partially decomposed before germination. The requirement for chilling suggests that germination of seeds in situ occurs in spring.

Comparative in vitro germination ecology of Calopogon tuberosus var. tuberosus (Orchidaceae) across its geographic range

“…For this reason, using non-orchid seed studies as framework to understand temperature effects on orchid seed germination is necessary. The role of constant temperatures has been examined in orchid seed germination (Harvais 1973;Rasmussen et al 1990;Rasmussen and Rasmussen 1991;Rasmussen 1992;Mweetwa et al 2008), but using constant temperatures may not reflect true environmental conditions (Baskin et al 2006). However, constant temperatures improved in vitro germination of several orchids over alternating temperatures (van Waes and Debergh 1986).…”

Evaluating asymbiotic seed culture methods and establishing Disa (Orchidaceae) germinability in vitro: relationships, requirements and first-time reports

“…Stratification 12 weeks at 5°C fi 25±2°C Coke (1990), Stoutamire (1990), Rasmussen (1992) and Chu and Mudge (1994) 8 weeks at 25±2°C fi 12 weeks at 5°C fi 25±2°C Illumination Continuous darkness Clements (1982), Van Waes and Debergh (1986b) and H. Crous (pers. comm.)…”

“…Alternatively, Rasmussen et al (1990) reported that temperate orchids required temperatures somewhat lower (< 20°C) than those reported elsewhere. Data are also available that have revealed the positive effects of cold and warm stratification seed treatments prior to long-term incubation (Withner 1959;Nakamura 1976;Hadley 1982;Fast 1982;Pritchard 1985;Ballard 1987; Van der Kinderen 1987;Van Waes 1987;Coke 1990;Stoutamire 1990;Yanetti 1990;Rasmussen 1992;de Pauw and Remphrey 1993;Miyoshi and Mii 1998). Many terrestrial species benefit from incubation in continuous darkness for a minimum defined period following sowing (Harvais and Hadley 1967;Fast 1982;Van Waes and Debergh 1986b;Ballard 1987;Van Waes 1987;Rasmussen et al 1990; Rasmussen 1992Rasmussen , 1995.…”

“…Data are also available that have revealed the positive effects of cold and warm stratification seed treatments prior to long-term incubation (Withner 1959;Nakamura 1976;Hadley 1982;Fast 1982;Pritchard 1985;Ballard 1987; Van der Kinderen 1987;Van Waes 1987;Coke 1990;Stoutamire 1990;Yanetti 1990;Rasmussen 1992;de Pauw and Remphrey 1993;Miyoshi and Mii 1998). Many terrestrial species benefit from incubation in continuous darkness for a minimum defined period following sowing (Harvais and Hadley 1967;Fast 1982;Van Waes and Debergh 1986b;Ballard 1987;Van Waes 1987;Rasmussen et al 1990; Rasmussen 1992Rasmussen , 1995. However, variants include continuous low-light treatments and a range of lowlight:dark photoperiods (Knudson 1943;Stoutamire 1963Stoutamire , 1964Stoutamire , 1974Arditti 1967Arditti , 1979Harvais 1972Harvais , 1973Clements 1982;Anderson 1991;Zettler and McInnis 1994).…”

“…'Green-podding' also removes the need for seed decontamination, which is desirable since some orchid seed displays sensitivity to decontaminants (Bergman 1995(Bergman , 1996Rasmussen 1995). However, exposure is not necessarily disadvantageous as chemical scarification increases the percentage germination in several Holarctic terrestrials (Stoutamire 1963;Harvais and Hadley 1967;Purves and Hadley 1976;Harvais 1980;Lindé n 1980;Arditti 1982;Van Waes and Debergh 1986a, b;Rasmussen 1992Rasmussen , 1995Miyoshi and Mii 1995).…”