Genotyping by sequencing reveals the genetic diversity of citrus cultivars cultivated in AlUla

AlUla region has a long cultural history dating back to the Nabatean civilization along the Silk Road. The introduction of citrus from Asia to the Mediterranean Basin probably take advantage of this ancestral road. More recently, citrus development projects have led to the introduction of multiple cultivars of citrus in Saudi Arabia and more particularly in the AlUla region. The traceability of these introductions has been lost and the objective of this study was to recover the identity of the cultivars grown in the AlUla region and to identify possible original cultivars that may have resulted from ancient interspecific hybridization related to cultural exchanges, including agriculture, along the Silk Road. Ninety-six local accessions were collected and genotyping by sequencing (GBS) was performed to obtain high-density genetic marker information both at nuclear and cytoplasmic level. We used the information of interspecific mosaic structure resulting from the reticulate evolution of cultivated citrus to identify the cultivars cultivated in AlUla by comparing the GBS data from AlUla with our previously established whole genome-sequencing (WGS) database. We successfully assigned the local accessions to height mandarins, three tangors, two tangelos, four lemons and four limes well known cultivars. One pure citron and nine pure pummelo accessions were identified. Additional WGS analysis are required to precise their diversity and origin. The local cultivar called ‘Toronge’ appears to be an admixture between C. maxima, C. reticulata and C. medica species with an interspecific pattern not previously described. It may be an original cultivar resulting from citrus germplasm exchange and hybridization along the Silk Road.