Watermelon
Crop Information
Biogeography
- 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.
