Why are the seeds of this species difficult? The seeds may have physiological dormancy, which can be overcome by mimicking the seasonal patterns of the species' native habitat. Removing the seed covering structures and incubating in the dark can have a beneficial effect on germination.
Citrullus lanatus (Image: RBG Kew)
This species has Orthodox seeds. To avoid a decline in viability, remove seeds from ripe fruits soon after harvest and allow to dry slowly, under ambient conditions, before transferring to a cool dry room. Dry to 15-20% eRH and store at -20ºC, or as cool as possible.
Germinate on agar, paper or sand at 25ºC or under an alternating temperature regime of 30/20ºC (with an 8/16hr photoperiod). If germination is slow, try removing the covering structures (including testa). Incubating the seeds in 24hr darkness may also help germination.
This species may be Physiologically Dormant (based on other species in the same genus). If dormancy is a problem, try 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 fruit is round, oval or oblong, with a light green to very dark green skin, variously patterned or striped, and red, yellow or orange flesh. The seeds are flat and smooth, varying in size, and may be white, tan, brown, black, red, green or mottled.
Accepted name: Citrullus lanatus (Thunb.) Matsum. & Nakai.
Synonyms: Citrullus vulgaris Schrad., Colocynthis citrullus (L.) Kunze
Common name: watermelon
References and Links
- 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.
- Janick, J. and Paull, R.E. (eds) (2008). The Encyclopedia of Fruit and Nuts. CAB International, UK.
- Rao, N.K., Hanson, J., Dulloo, M.E., Ghosh, K., Nowell, D. and Larinde, M. (2006). Manual of seed handling in genebanks. Handbooks for Genebanks No. 8. Bioversity International, 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: Citrullus lanatus.
- AVRDC - The World Vegetable Centre, Taiwan: fact sheet on Citrullus lanatus.
- PROTAbase (Plant Resources of Tropical Africa) - Wageningen, Netherlands: Citrullus lanatus.
- SID (Seed Information Database) - Royal Botanic Gardens, Kew, UK: Citrullus lanatus.
- Tropicos - Missouri Botanical Garden, USA: Citrullus lanatus.