Northeast Brazil: A secondary center of diversity for watermelon (Citrullus lanatus)

Watermelon originated in Africa where its main diversity center is located. It was introduced to NE Brazil around three centuries ago by African slave s. The study of watermelon evolution after its introduction in NE Brazil in dicated that three main factors have played their part: historical (slave t rading and colonization of the region); genetical (seed dormancy, introgres sive hybridization, fruit opening in the field, natural and artificial sele ction), and ecological (seed dispersal by animals, watermelon as source of water by farmers in the field, seed bank, different physical environments). These factors, solely or together, determined the selection, maintenance a nd amplification of the watermelon's genetic variability in the traditional farming of NE Brazil, on the basis of the farmers' fields as units for evo lution.