Résumé
This study provides the first analysis of the level and patterns of nucleotide polymorphism of the NCED1 gene in grapevine (Vitis vinifera L.). A total of 123 sequences of the gene were analyzed to give a sample of 50 wild accessions and 73 cultivars. A high single nucleotide polymorphism and haplotype diversity was revealed in the cultivars studied, especially Tunisian germplasms which present an important and diverse reservoir of genetic diversity for grape breeding and conservation. The haplotype distribution highlights two origins of the cultivars studied: one may be related to primary grapevine gene pool domestication while the second seems to be more recent. Thus, besides domestication, gene introgression has also played a role in shaping the current varietal landscape of grape cultivars. Higher nucleotide and haplotype polymorphism was recorded for cultivars. This was accompanied by a higher recombination rate in cultivated grapevines for this gene, a recent selective sweep in wild samples and a balancing selection in cultivars. The conservation of genetic diversity of the endangered wild germplasm is important to ensure that the wild population can be used in future breeding programs of the domesticated cultivars. The high number of alleles discovered can be used as a valuable source for association studies between allele frequencies and phenotypic variations in this gene. In addition to natural selection, molecular evidence shows that genetic variation in this locus appears to be shaped by a combination of mutation and recombination events.