A Hot Spot of Olive Biodiversity in the Tunisian Oasis of Degache

Abstract

Tunisia is one of the world’s largest producers of olive oil, and it preserves pools of olive genetic diversity that are still unexplored. A recent prospection and collection program of the National Gene Bank of Tunisia (NGBT) focused on the vast oasis of Degache, in the south west part of Tunisia, where 47 samples were collected and genetically characterized through simple sequence repeat (SSR) markers. Identification and authentication of genotypes were obtained through comparison with reference cultivars belonging to the Olive National Collection of Tunisia (IOC) and with cultivars from Algeria, Italia, Syria and Lebanon. Degache olive genotypes showed large genetic variability, a significant diversity from the reference germplasm, and a clear differentiation from modern varieties. The population structure analysis identified four gene pools characterizing genotypes from different area of origin. Two gene pools appear to be more represented in germplasm from southern Tunisia, where environmental conditions at critical plant development phases, are harsher. This suggests that this germplasm might present traits of adaptation useful for breeding to improve resilience to abiotic stresses. Our results will support ex situ and in situ conservation activities of Tunisian olive germplasm pursued by the National Gene Bank of Tunisia.

Applications of Microsatellite Markers for the Characterization of Olive Genetic Resources of Tunisia

“…On the contrary, focusing on the characterization of South East Tunisian germplasm, Ben Mohamed et al [ 76 ], and Ben Ayed et al [ 77 ] highlighted a lack of correlation between genetic and geographical origin of olive cultivars in Tunisia. Other authors [ 78 ] have shown the clustering of cultivars from the same or a nearby region, suggesting a common genetic base of these cultivars. This is in agreement with the hypothesis of autochthonous origin of most of the olive cultivars as well as their limited diffusion from their centers of origin [ 79 ].…”

“…The research pointed out, in this unknown germplasm, gene pools not present in commercial (Nurseries) varieties, underlining the need to broaden the genetic base of the commercialized germplasm to avoid genetic erosion of this olive patrimony. In addition, Saddoud Debbabi et al [ 78 ] the genetic diversity of the olive germplasm of the oasis of Degache, in the south west part of Tunisia, characterized by arid climate and low pluviometry (<100 mm/year), showing the presence of olive genotypes largely diverse from the reference germplasm, including the traditional cultivar of Chetoui and Chemlali, but also from other modern varieties [ 78 ]. The population structure analysis identified two gene pools more represented in germplasm from southern Tunisia, where environmental conditions at critical plant development phases, are harsher.…”

How to Choose a Good Marker to Analyze the Olive Germplasm (Olea europaea L.) and Derived Products

“…In the last decades, the growing need to preserve the existing germplasm from genetic erosion resulted in the building of the large world germplasm collections, such as the World Olive Germplasm Banks (WOGB) at IFAPA (Cordoba, Spain) and Marrakech (Morocco), besides many small collections created in Europe [54,[107][108][109], Northern America [110,111], Southern America [112], Australia [113], Northern Africa [114][115][116][117], the Middle East [118,119], the Balkan area [24,120,121], Iberia [122,123]. SSRs have been the marker of choice for genotyping these genetic resources.…”

Current Status of Biodiversity Assessment and Conservation of Wild Olive (Olea europaea L. subsp. europaea var. sylvestris)

“…From all the studies about oleaster carried out so far, some key concepts have emerged and they are summarized in Table 2. The evaluation and characterization of local wild germplasm populations performed in these studies pointed out the great importance and relevance of these collections, as they represent a great source of genetic variability [14,47,74].…”