A 3500-year-old leaf from a Pharaonic tomb reveals that New Kingdom Egyptians were cultivating domesticated watermelon

Abstract

19 Domestication of the watermelon (Citrullus lanatus) has alternatively been placed in South 20 Africa, the Nile valley, or more recently West Africa, with the oldest archeological evidence 21 coming from Libya and Egypt. The geographic origin and domestication of watermelons has 22 therefore remained unclear. Using extensive nuclear and plastid genomic data from a 3,560-23 year-old Citrullus leaf from a mummy's sarcophagus and skimmed genomes for 24 representatives of the seven extant species of Citrullus, we show that modern cultivars and the 25 ancient plant uniquely share mutations in a lycopene metabolism gene (LYCB) affecting pulp 26 color and a stop codon in a transcription factor regulating bitter cucurbitacin compounds. This 27 implies that the plant we sequenced had red-fleshed and sweet fruits and that New Kingdom 28 Egyptians were cultivating domesticated watermelons. The genomic data also identify extant 29 Sudanese watermelons with white, sweet pulp as the closest relatives of domesticated 30 watermelons. 31 32 Archaeogenomics | plant domestication | ancient plant genome | Africa | New Kingdom Egypt 33 | Pharaonic tomb 34 35 Significance statement [120 words] 36 With some 197.8 million tons in 2017, watermelon, Citrullus lanatus, is among the World's 37 most important crops, yet its area of origin and domestication have remained unclear, with 38 competing hypotheses favoring South Africa, West Africa, Central Africa, or the Nile valley. 39 We generated extensive nuclear and plastid genomic data from a 3500-year-old leaf from a 40 Pharaonic sarcophagus and performed genome skimming for representatives of all other 41 Citrullus species to compare key genes involved in fruit bitterness and color. White-fleshed, 42 non-bitter melons from southern Sudan are the closest relatives of domesticated watermelon, 43 and the ancient genome shares unique alleles with a red-fleshed, non-bitter domesticated form 44 (but no wild forms), implying that 18 th Dynasty Egyptians were cultivating domesticated 45 watermelon by 3500 years ago. 46

Origin and domestication of Cucurbitaceae crops: insights from phylogenies, genomics and archaeology

“…A phylogenetic analysis of Citrullus (Chomicki & Renner, ), together with genetic, archaeological and historical data (reviewed by Paris, ) rejects the first two hypotheses, leaving West Africa and Northeast Africa. Phylogenomic analyses of nuclear gene sequences suggested that the white‐fleshed Sudanese Kordophan melon is the closest relative of the domesticated watermelon (Renner et al ., ; Fig. ).…”

“…The phylogeny results from a maximum likelihood (ML) analysis of 143 nuclear loci from Renner et al . () with ML bootstrap values shown at branches. ML analysis of a matrix with 100 plastid loci yielded the same topology, with high bootstrap support at all nodes.…”

Georeferenced phylogenetic analysis of a global collection of wild and cultivated Citrullus species

“…The lack of haplotype divergence within C. lanatus and C. mucosospermus is likely the result of selection or other bottlenecks in the domestication histories of watermelon and egusi melon. Certainly, selection for sweet red-fleshed cultivars with high lycopene content or selection of seed type as source of protein/oil for consumption might contribute to current genetic structure in those cultivated species (Achigan-Dako et al, 2015;Renner et al, 2019).…”

“…Over the last two decades, questions regarding the origin and taxonomy ofCitrullus spp. have fuelled numerous studies to clarify phylogenetic relationships and nomenclature, identify wild relatives, and determine both centers of origin and divergence times (Jarret et al, 1997;Jarret & Newman, 2000;Levi et al, 2001;Levi et al, 2004;Levi & Thomas, 2005;Solmaz & Sari, 2009;Dje et al, 2010;Solmaz et al, 2010;Nesom, 2011;Levi et al, 2013;Mujaju et al, 2013;Hammer & Gladis, 2014;Chomicki & Renner, 2015;Renner et al, 2019;Chomicki et al, 2020). Despite these efforts, uncertainty vis-à-vis these questions remains as no wild relatives were found neither in west nor in northern east Africa; and comparatively few studies have focused on the distribution of the genetic variation within Citrullus or the likely colonization routes of various species within the genus.…”

“…lanatus , a claim at odds with earlier assertions. Indeed, whereas some experts believe watermelon originated from southern Africa, based on the distribution of wild relatives in the Namibian desert (Bates & Robinson, 1995), others point to northern or north-east Africa, especially the Nile river area in Sudan, as the likely center of origin based on archaeological data (Wasylikowa & Van Der Veen, 2004;Paris, 2015;Renner et al, 2019). According to these latter studies, very few archaeological records of watermelon are known from southern Africa; and all date to a relatively recent period between the 8 th and 13 th centuries A.D.…”