Biogeography and Origin
Watermelon Crop Information
- by Todd C. Wehner
- Department of Horticultural Science
- North Carolina State University
- Raleigh, NC 27695-7609
Watermelon is thought to have originated in southern Africa because it is found growing wild throughout the area, and reaches maximum diversity of forms there. It has been cultivated in Africa for over 4,000 years. In 1857, David Livingstone reported watermelon growing profusely in the Kalahari Desert (Namibia and Botswana) after unusually heavy rainfall (as cited by Fursa). The natives there knew of sweet as well as bitter forms growing throughout southern Africa. De Candolle, in 1882, considered the evidence sufficient to prove that watermelon was indigenous to tropical Africa, more specifically the Southern parts of Africa.
Citrullus colocynthis is considered to be a wild ancestor of watermelon, and is now found native in north and west Africa. Fruit are small, with a maximum diameter of 75 mm (3 inches). The flesh is bitter and the seeds are small and brown. Shimotsuma found that crosses of C. lanatus with C. colocynthis produced F1 hybrids with nearly regular meiosis. The pollen was 30-40% fertile, and 35% of the seeds were fertile.
Although Citrullus species grow wild in southern and central Africa, C. colocynthis also grows wild in India. India and China may be considered secondary centers of diversity for the genus. Cultivation of watermelon began in ancient Egypt and India, and is thought to have spread from those countries through the Mediterranean, Near East, and Asia. The crop has been grown in the United States since 1629.
Germplasm is the foundation of breeding programs, so germplasm collection and evaluation are important aspects of breeding. The following regions have been prioritized for collection of Citrullus germplasm:
- India: Indo-Gangetic plains and areas in the Northwest parts of India
- Africa: South and Southwest (Kalahari Region)
- Southern areas of the former USSR and Iran
- Tropical Africa
Recent work in germplasm collection and exchange has provided the U.S.D.A. germplasm system with a total of 51 Citrullus accessions were collected during a scientist exchange visit with the People’s Republic of China led by Wehner in 1993. Later, a team of four researchers led by Wehner in 1996 collected germplasm of Citrullus in the Republic of South Africa.