The present study was carried out to evaluate and characterize, for the first time, the genetic potential of a collection of onion (Allium cepa L.) local accessions from the arid region of southern Tunisia. The genetic diversity among 135 onion individuals, belonging to 23 accessions, was evaluated using microsatellite (SSR) markers and phenotypic information. A total of 35 alleles were generated with 11 SSRs. The polymorphic information content (PIC) value ranged from 0.08 to 0.95, with an average PIC of 0.43. The expected heterozygosity averaged 0.37, and the observed heterozygosity averaged 0.42. The analysis of molecular variance (AMOVA) revealed that 79% of genetic variation existed within individuals. Structure and cluster analysis grouped the accessions into two major clusters: landraces and pre-breeding lines. For the phenotypic traits evaluated, field trials were conducted in two different environments. Significant differences among accessions were shown, and for most traits, there was also a significant environmental effect and a significant interaction between environment and accession. Great variability was found for all the traits that could be exploited to create new varieties of onion adapted to local conditions by selecting appropriate parents in hybridization breeding.

Nineteen Tunisian onion genotypes were characterized based on phytochemical composition, sugar content, and antioxidant activity. The studied onions showed a great diversity on biochemical contents and composition. It seemed that there were differences between genotype categories (local landraces or local breeding lines) and within the same category. Quercetin and quinic acid were, respectively, the main flavonoid (flavonol) and organic acid (cyclitol) identified and quantified by HPLC. In all studied onions, quercetin was the predominant flavonoid, with the highest content in the local breeding line OP2-w (1142.19 mg 100 g-1 DW). OP3-w showed the highest value of total phenolic as well as total flavonoid content at 12.52 mg GAE g-1 DW and 48.28 RE g-1 DW respectively. Fructose and sucrose were the most abundant sugars in all the genotypes. Clustering and PCA analysis showed a great dispersion of these genotypes which were classified into 3 major groups. The chemical and nutritional composition found highlights the great value of this onion germplasm which can be used for the sustainable conservation and management of Tunisian onion genetic resources.