Why are the seeds of this species difficult? This species has recalcitrant seeds, which have a high critical moisture content and will rapidly lose viability if they are dried.
Theobroma cacao (Image: RBG Kew)
This species has Recalcitrant seeds which cannot be dried without causing a decline in viability. Do not place the seeds under sub-zero temperatures as they will suffer from freezing damage due to their high moisture content.
Researchers have found that the seeds have an initial seed moisture content of 43%. Store seeds in their pods at around 17°C, maintaining a high moisture content (40-45% mc). Under these conditions they will remain viable for at least three weeks. Viability has been found to decline at moisture contents below this and the seeds will not survive desiccation to below 20% moisture content. The embryonic axis of the seed is killed on desiccation to 17% mc.
The seeds of this species do not display dormancy. The seeds normally germinate as soon as they reach maturity, sometimes in the pod, and are only viable for a short time.
Before sowing, remove the testa and try rubbing with sand, wood ash or coconut fibre to reduce the amount of mucilage. Sow the seeds on sand, with the hilum scar facing downwards or horizontally. Germinate on sand under an alternating temperature regime of 30/25ºC (ambient room temperature), with 24hr light.
The fruit is an indehiscent drupe, varying in size (10-32 cm) and shape, from nearly spherical to cylindrical, pointed or blunt, smooth or warty, with or without 5-10 furrows. The pericarp is usually fleshy and thick with mesocarp, varying in the amount of lignification.
The seeds or beans (20-60 per pod) are arranged in 5 rows. They are variable in size (2-4 x 1.2-2 cm), shape (ovoid or elliptic) and colour, with white to deep purple cotyledons. The embryo develops at a late stage, using up the endosperm.
The young green pods ripen to yellow, and red pods turn orange. The pods reach full size at 4-5 months after fertilisation and require another month for ripening. The seeds rattle inside the ripe pods. When the seeds are mature, they contain two large convoluted cotyledons, a small embryo, a thin membrane which is the remains of the endosperm and a leathery testa (skin or shell). The fresh seeds are surrounded by a mucilaginous, sugary pulp (white in colour) which develops from the outer integument of the ovule.
Accepted name: Theobroma cacao L.
Common name: cocoa
References and Links
- Baskin, C.C. and Baskin J.M. (1998). Seeds: ecology, biogeography, and evolution of dormancy and germination. Academic Press, USA.
- Chirco E. and Turner T. (1986). Species without AOSA Testing Procedures. The Newsletter of the Association of Official Seed Analysts, Vol 60 (2): pp2-66.
- Janick, J. and Paull, R.E. (eds) (2008). The Encyclopedia of Fruit and Nuts. CAB International, UK.
- Purseglove, J.W. (1968). Tropical Crops: dicotyledons. Longman Group Ltd., UK.
- AFPD (African Flowering Plants Database) - Conservatoire et Jardin Botaniques de la Ville de Genève, Switzerland, and South African National Biodiversity Institute, Pretoria, RSA: Theobroma cacao.
- SID (Seed Information Database) - Royal Botanic Gardens, Kew, UK: Theobroma cacao.
- Theobroma cacao (cocoa tree) - Species profile from Kew
- Tropicos - Missouri Botanical Garden, USA: Theobroma cacao.