I.M. Pinker, T. Degischer, A.-Chr. Rath and R. Schenk
Humboldt-Universität zu Berlin, Albrecht Daniel Thaer-Institute, Germany

SUMMARY Actaea racemosa L. (syn. Cimicifuga racemosa (L.) Nuttal) or black cohosh is a perennial plant of the buttercup family (Ranunculaceae) growing wild in deciduous forests of North America. Because mature seeds of A. racemosa have a rudimentary embryo and exhibit deep simple epicotyl morphophysiological dormancy, germination is a long-lasting process requiring warm–cold stratification. The study has been conducted in 2015–2016 and aimed to develop an efficient germination protocol. For imbibition, graded seeds (1.22–2.5 mm in length) were incubated in tap water or aqueous gibberellic acid solution for 12 hours. The imbibed seeds were kept in darkness at 23°C for 4 weeks (warm phase) followed by 4 weeks of incubation at 14°C or 7°C (cold phase) in darkness or light. Most embryos in mature seeds were developed to the heart stage. They reached after 4 weeks of warm phase the torpedo stage. During the following cold phase, the embryo development was more pronounced in seeds imbibed in gibberellic acid. This promoting effect of gibberellic acid showed a dose-effect response. Application of 2 g L-1 gibberellic acid resulted in germination of around 60% seeds after 4 weeks of cold phase while 1 g L-1 gibberellic acid caused germination of up to 20% seeds. Due to the application of 2 g L-1 gibberellic acid to the imbibition solution the germination of most seeds was possible after 8 weeks warm–cold stratification. The observation of the embryo development proved the promoting effect of gibberellic acid, especially during the cold phase. Keywords Cimicifuga racemosa (L.) Nuttal, epicotyl dormancy, GA3, imbibition, stratification temperature, warm–cold stratification

Significance of this study What is already known on this subject? Actaea seeds exhibit deep simple epicotyl morphophysiological dormancy and need warm–cold stratification to germinate. Most authors used fluctuating temperatures during warm- and cold phase for some months each. Germination is long lasting (minimum 5 to 6 months). For the effect of gibberellic acid on germination there are only very few and conflicting reports. In these reports, gibberellic acid concentration used was not always indicated or rather low concentrations were applied, e.g., 2–4 mg L-1. Gibberellic acid was so far applied continuously during warm- and cold phase, respectively. What are the new findings? This is the first report showing the effect of a high concentration of gibberellic acid applied only during imbibition for 12 hours on embryo development during warm- and cold phase. The embryo development was accelerated in samples imbibed in gibberellic acid solution especially during the cold phase. Germination (emergence of radicle and plumule) started in these samples after 7 weeks already. The application of gibberellic acid to the imbibition solution supported the effect of warm–cold stratification regarding dormancy breaking and reduced the required stratification time considerably. Four weeks of warm phase (23°C) followed by 4 weeks cold phase (14°C or 7°C) were sufficient to get around 60% germination after 8 weeks already. The germination continued during the following 2 weeks and the percentage of germinated seeds increased. What is the expected impact on horticulture? Actaea racemosa is a valuable medicinal plant used in phytotherapy, especially against climacteric symptoms. Field production for A. racemosa should be established to substitute its harvest from the wild. However, young plant production is still the bottleneck for field production. With this protocol, young plant production can be accelerated considerably and moreover, young plants can be produced in time effectively in large amounts for field production.

Supplemental information

• Editorial eJHS 86(1) and tribute to Jens Wünsche

E-mail: ina.pinker@cms.hu-berlin.de  

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Received: 14 November 2019 | Accepted: 6 April 2020 | Published: 15 February 2021 | Available online: 15 February 2021