Molecular and morphological characterisation of the oldest Cucumis melo L. seeds found in the Western Mediterranean Basin

In 2008–2009, a rescue excavation uncovered an intact Late Bronze Age well in Sa Osa, Sardinia (Italy). The structure yielded a large number of waterlogged plant remains, of which a group of melon seeds (Cucumis melo L.) were some of the most remarkable. These seeds represent the earliest recorded remains of this taxon in the Western Mediterranean and are some of the oldest ever recorded. The plant remains were preserved in anoxic conditions and were found in a perfect state of conservation, making them ideal candidates for morphometric and molecular characterisation. A total of 96 parameters, measured using an automatic image analysis system, were specifically designed to evaluate the morphological features of 15 preserved whole seeds. DNA extraction from archaeological samples followed a procedure specifically set up to avoid any kind of contamination. A 123-SNP genotyping platform that had been validated previously was used. The morphological and molecular data of the archaeological seeds were successfully compared with those of a set of 179 accessions, including landraces, of feral and wild melons from Europe, Africa, and Asia. Both analyses confirmed that these ancient seeds did not belong to a wild melon, but instead to a cultivated one. This primitive melon could have belonged to a group of ancestral non-sweet or semi-sweet forms of chate, flexuosus, or ameri varieties, showing similarities to North African and Central Asian accessions. This finding is coherent with the reportedly important role of cucumber-like melons in the species’ diversification process and with the accepted role of the ameri group as the ancestors of the modern sweet varieties.