Tracking the evolutionary history of the Allium ampeloprasum L. complex (section Allium) provides evidence of the contribution of North African diploids to the formation of allopolyploid horticultural groups

The economically important Allium ampeloprasum L. represents a polyploid complex, comprising hexa- and octoploid Great Headed Garlic horticultural cultivars (6x-8x GHG) and several traditional varieties of the tetraploid (4x) leeks (Leek, Bulbous leek, Kurrat and Pearl onion). Its wild representatives were indicated as rare in the Mediterranean region. This study aims to explore the diversity and origin of polyploidy in this complex, including its wild relatives A. baeticum Bossier and A. guttatum Steven with particular focus on the poorly investigated North-African region. Natural populations were sampled in Algeria in various bioclimatic conditions, then subjected to karyological and molecular phylogenetic analyses based on nuclear rDNA ITS region and chloroplast trnL-trnF and trnD-trnT intergenic spacers. Comparative analyses included available Genbank accession sequences representing old-world relatives. Chromosome count surveys revealed an unexpected higher occurrence of diploid (2n = 16) than tetraploid (2n = 32) cytotypes. The phylogenetic analyses first allowed positioning the Algerian material within the A. ampeloprasum complex. Interestingly, all the Algerian diploid and tetraploid populations from A. ampeloprasum and A. baeticum form a distinct monophyletic group. The results provide novel and robust evidence demonstrating that the North African diploid A. ampeloprasum genetic pool widely contributed as a source of progenitors not only for the A. ampeloprasum and A. baeticum Algerian tetraploids, but also in the formation of the GHG and Leek cultivated allopolyploids. Therefore, the North African populations emerge as an important reservoir of new wild genetic resources of great interest for tracing the origin of crop domestication and for breeding programs of cultivated varieties.