Why are the seeds of this species difficult? Some species of the Poaceae family can produce a high proportion of empty seeds, which collectors and curators must take account of. The seeds may have physiological dormancy, which can be overcome by mimicking the seasonal patterns of the species' native habitat.
Setaria sphacelata (Image: H. Morales, RBG Kew)
This species has Orthodox seeds - dry to 15-20% eRH and store at -20ºC, or as cool as possible.
Remove the seed covering structures if necessary. Germinate on agar, germination paper or sand, under alternating temperature regimes of 30/20°C or 35/20°C (with an 8/16hr photoperiod). It may be necessary to add 101 mg/l potassium nitrate to the germination medium to encourage growth. Perform a cut-test on any seeds that have not germinated, to check for empty seeds. All empty seeds are non-viable in germination tests.
The seeds of this species may be Physiologically Dormant (based on other species in the same genus). If germination is low, this type of seed dormancy can be overcome by mimicking the seasonal patterns of the species' native habitat. Use a moist pre-chill or pre-heat treatment (depending on local climatic conditions) or a dry after-ripening treatment, before germinating the seeds on agar, germination paper or sand at their optimum temperature. If this does not work, you can perform delicate surgery to enable the embryo to grow. Excise the tissue near the root tip.
The occurrence of empty seeds is common in wild-collected accessions of some Poaceae species. Empty seeds may have a normal seed coat but an absent or under-developed embryo, or limited storage tissue.
The fruit is an indehiscent caryopsis with lemma and palea attached, which, along with the pericarp, offer mechanical protection to the seed. The seed (2.03-2.22 mm x 0.64-0.70 mm x 0.95-1.01 mm) is grey with a smooth, slightly reticulate surface and is ovoid in shape, with a flat ventral side. The seed configuration is anatropous. The translucent embryo is basal-lateral, occupying a quarter or more of the seed volume.
See more images of this species at the Digital Atlas of Economic Plants.
Setaria sphacelata section
(Image: H. Morales, RBG Kew)
Accepted name: Setaria sphacelata (Schumach.) Stapf & C.E.Hubb. ex M.B.Moss
Common name: African bristlegrass
References and Links
- Black, M., Bewley, J.D. and Halmer, P. (2006). The Encyclopaedia of Seeds: science, technology and uses. CAB International, UK.
- Food and Agriculture Organization of the United Nations and International Plant Genetic Resources Institute (1994). Genebank Standards. FAO/IPGRI, Rome, Italy.
- International Seed Testing Association (2010). International Rules for Seed Testing: edition 2010. ISTA, Bassersdorf, Switzerland.
- AFPD (African Flowering Plants Database) - Conservatoire et Jardin Botaniques de la Ville de Genève, Switzerland, and South African National Biodiversity Institute, Pretoria, RSA: Setaria sphacelata.
- PROTAbase (Plant Resources of Tropical Africa) - Wageningen, Netherlands: Setaria sphacelata.
- SID (Seed Information Database) - Royal Botanic Gardens, Kew, UK: Setaria sphacelata.
- Tropical Forages - CSIRO, DPI&F(Qld), CIAT and ILRI, Brisbane, Australia: Setaria sphacelata var. splendida.
- Tropicos - Missouri Botanical Garden, USA: Setaria sphacelata.