Why are the seeds of this species difficult? The seeds may have both physical and physiological dormancy. For germination to occur, both types of dormancy may need to be broken.
Sclerocarya birrea fruit (Image: W. Stuppy, RBG Kew)
This species most probably has Orthodox seeds. Researchers have found that the seeds will tolerate drying to a low moisture status and can be stored at sub-zero temperatures without a decline in viability. Dry to 15-20% eRH and store at -20ºC, or as cool as possible.
The seeds of this species may have Combinational Dormancy, due to their impermeable seed coats (physical dormancy) and potentially physiologically dormant embryos (based on other species in the same genus).
Locate the operculum by filing the endocarp, then use a hammer and steel scalpel to prise off the operculum and expose the seed. Germinate on agar, germination paper or sand at 25 to 30ºC. Acid scarification with hydrochloric acid can also be used to break down the seed coat and improve germination.
If germination is low, overcome physiological dormancy with a dry after-ripening treatment immediately after harvest, at 25ºC for 18 months, before germinating the seeds on agar, germination paper or sand at their optimum temperature. This will allow post-harvest development to take place.
Sclerocarya birrea seed
(Image: W. Stuppy, RBG Kew)
The fruit (30—40 mm) is a specialised drupe. The stone is embedded in a fibrous, juicy mesocarp. One to four fruit locules occur in the hard endocarp, each appearing to be a hermetically sealed unit, with an orifice closed by a small operculum. Each locule contains a single seed, covered with a thin, papery seed coat. The diameter of the orifice is always smaller than that of the seed so it is impossible to remove intact seeds from the fruit. During germination, the embryo emerges through this orifice.
The fruits drop from the tree when still green, ripening to pale yellow on the ground.
See more images of this species at the Digital Atlas of Economic Plants.
Accepted name: Sclerocarya birrea (A. Rich.) Hochst.
Synonyms: Sclerocarya caffra Sond.
Common name: maroola plum
References and Links
- Gaméné, C.S., Erdey, D., Baxter, D., Motete, N., Berjak, P. (2004). Desiccation, germination and storage of Sclerocarya birrea seeds from Burkina Faso. In M. Sacandé, D. Joker, M. Dulloo and K. Thompsen (eds) Comparative Storage Biology of Tropical Tree Seeds. IPGRI, Rome, Italy.
- Food and Agriculture Organization of the United Nations and International Plant Genetic Resources Institute (1994). Genebank Standards. FAO/IPGRI, Rome, Italy.
- AFPD (African Flowering Plants Database) - Conservatoire et Jardin Botaniques de la Ville de Genève, Switzerland, and South African National Biodiversity Institute, Pretoria, RSA: Sclerocarya birrea.
- Forest & Landscape Denmark - University of Copenhagen, Denmark: seed leaflet on Sclerocarya birrea.
- PROTAbase (Plant Resources of Tropical Africa) - Wageningen, Netherlands: Sclerocarya birrea.
- SID (Seed Information Database) - Royal Botanic Gardens, Kew, UK: Sclerocarya birrea.
- Tropicos - Missouri Botanical Garden, USA: Sclerocarya birrea.