Georeferenced phylogenetic analysis of a global collection of wild and
cultivated Citrullus species
The geographical origin of watermelon (Citrullus lanatus) remains
debated. While a first hypothesis suggests the center of origin to be
west Africa, where a sister endemic species C. mucosospermus thrives, a
second hypothesis suggests north-eastern Africa where the white-fleshed
Sudanese Kordophan melon is cultivated. In this study, we infer
biogeographical and haplotype genealogy for C. lanatus, C.
mucosospermus, C. amarus, and C. colocynthis using non-coding cpDNA
sequences (trnT-trnL and ndhF-rpl32 regions) from a global collection of
135 accessions. In total, we identified 38 haplotypes in C. lanatus, C.
mucosospermus, C. amarus, and C. colocynthis; of these, 21 were found in
Africa and 17 appear endemic to the continent. The least diverse species
was C. mucosospermus (5 haplotypes) and the most diverse was C.
colocynthis (16 haplotypes). Some haplotypes of C. mucosospermus were
nearly exclusive to West-Africa, and C. lanatus and C. mucosospermus
shared haplotypes that were distinct from those of both C. amarus and C.
colocynthis. The results support previous findings C. mucosospermus to
be the closest relative to C. lanatus (including subsp. cordophanus).
West Africa, as a center of endemism of C. mucosospermus, is an area of
interest in the search of the origin of C. lanatus. This calls for
further historical and phylogeographical investigations and wider
collection of samples in West and North-East Africa.