Genetic and Phenotypic Diversity and Evaluation of Total Phenolics and Antioxidant Properties of Garlic Landraces from Lazio Region (Central Italy): “Aglio Rosso di Proceno” and “Aglio Rosso di Castelliri”

Garlic (<i>Allium sativum</i> L.) is the second most significant species within the <i>Allium</i> genus worldwide, widely used in cooking and both traditional and modern medicine due to its beneficial biological and therapeutic properties. In Italy, diverse pedo-climatic conditions and historical–cultural fragmentation have led to the development of various garlic landraces, prized for their unique organoleptic qualities and cultural importance. This study aimed to assess the intra-varietal diversity and uniqueness of two red garlic landraces from the Lazio region in central Italy, “Aglio Rosso di Castelliri” and “Aglio Rosso di Proceno”, using SSR and ISSR molecular markers, along with evaluations of bulb morphological traits, total phenolic content, and antioxidant properties. The molecular analysis included 11 accessions of “Aglio Rosso di Castelliri”, nine of “Aglio Rosso di Proceno”, and 15 control accessions, comprising eight Italian red-type garlic landraces, four Spanish red garlic commercial varieties, two white garlic accessions, and an accession of <i>A. ampeloprasum</i> var. <i>holmense</i> used as an outgroup. SSR and ISSR markers revealed moderate genetic diversity within the collection, with mean PIC values of 0.41 and 0.17, respectively. The molecular data identified four distinct genetic clusters, with the two Lazio landraces forming separate groups, indicating their genetic distinctiveness. The results from the STRUCTURE analysis support the hypothesis that these landraces may have originated from the widely cultivated “Aglio Rosso di Sulmona” or a common ancestral population once prevalent in central Italy. The study also revealed significant intra-population genetic diversity within the two garlic landraces, underscoring the need for in situ conservation and clonal selection. Phenotypic evaluations confirmed the distinctiveness of the two landraces, with “Aglio Rosso di Castelliri” characterized by smaller bulbs and cloves with higher dry matter content and distinct color profiles. Additionally, significant variation in total phenolic content and antioxidant activity was observed by analyzing 13 selected accessions from the two landraces (six from “Aglio Rosso di Proceno” and seven from “Aglio Rosso di Castelliri”) and five red garlic control accessions, with the two Lazio landraces exhibiting higher levels than the control group. This study highlights the importance of integrating molecular, phenotypic, and chemical analyses to understand garlic landrace diversity, with significant implications for their conservation and protection of local agro-food products.