Egusi Watermelon Type (and Citrullus lanatus vs. Citrullus colocynthis)

Watermelon Crop Introduction

  • by Gabriele Gusmini and Todd C. Wehner
  • Department of Horticultural Science
  • North Carolina State University
  • Raleigh, NC 27695-7609

Some watermelon accessions in the USDA-ARS germplasm collection show a particular phenotype usually described by breeders as Egusi seed type. These accessions have been misclassified on occasion. Typically, Colocynthis citrullus [=Citrullus lanatus] has been confused with Citrullus colocynthis and as a result, the Egusi watermelon has been sometimes mistakenly considered a common name for Citrullus colocynthis.

Citrullus lanatus (Thunb.) Matsum. & Nakai var. lanatus [=Colocynthis citrullus L.] is the cultivated watermelon, and can have Egusi phenotype. On the other hand, Citrullus colocynthis Schrad. is a different Citrullus species (commonly called colocynth) It should not be referred to as egusi melon. Colocynth grows wild in warm and arid areas of Africa and Asia.

The Egusi watermelon (Citrullus lanatus (Thunb.) Matsum. & Nakai) is commonly known in Nigeria and the Congo as wild watermelon, Egusi melon, or Ibara. Egusi watermelon is widely cultivated in Nigeria, where the protein- and carbohydrate-rich seeds are used as a regular part of the diet. The fruit are not edible because of their bitter, hard, white flesh.

The origin of the Egusi phenotype is uncertain, and the developmental genetics of this seed phenotype are not known. Its seeds are coated by an adherent layer of tissues that may be remnants of nucellar tissues. The tissues are visible only after the second to third week of seed development, and can be removed at maturity for commercial use of the seeds. The trait is controlled by a single, recessive gene called egusi seed (eg), where eg comes from PI 490383 selection NCG-529 and PI 560006, and Eg comes from ‘Calhoun Gray’ and ‘Charleston Gray’.